Jean-Christophe Bach

Émilie Balland

Paul Brauner

Radu Kopetz

Pierre-Etienne Moreau

Antoine Reilles

Algebraic terms > Hooks > Mappings > Graphs Tom Documentation Guided Tour :: Tutorial :: Language Reference :: Tools The grammar is the following: IncludeConstruct ::= '%include' '{' FileName '}'

Keywords:

Name ',' Name ')' GoalLanguageBlock Note: since version 2.5, is_fsym and make functions are optional (therefore the %op construct could be empty).

When not declared, is_fsym default value is false. When nothing is declared, there is a make default value: a call to the function which has the same name as the considered operator. This shortcut is useful to provide type information about a Java function for example.

Predefined sorts and operators

See Section Predefined mappings in the Runtime Library Chapter.

Gom construct

The grammar for the Gom construct is as follows: GomConstruct ::= '%gom' ['(' OptionString ')'] '{' GomGrammar '}'

Guided Tour

Documentation:Basic Usage Doc : Guided Tour Algebraic terms > Hooks > Mappings > Graphs

We provide here cut and paste examples, each of them illustrates one particular aspect of the tom language. Every code snippet comes with the command line to compile and execute it along with the associated program output. // the sort of p is inferred out of the patterns %match(p) { // variable instances are accessed with ` P(t) -> { return "P(" + prettyTerm(`t) + ")"; } Q(var("x")) -> { System.out.println("I was here !"); } /* since the previous rule does not break the flow (with a return statement), tom still looks for matching patterns in their declaration order */ Q(t) -> { return "Q(" + prettyTerm(`t) + ")"; } implies(p1,p2) -> { return "(" + prettyProposition(`p1)

Algebraic terms in

+ " => " + prettyProposition(`p2) + ")"; } } return ""; // this case never occurs, but javac isn't aware of it StrList l = `strlist("framboisier","eric","framboisier","remi", "remi","framboisier","rene","bernard"); System.out.println(l); /* We compute a fixpoint for the rewrite system 'Remove' applied in head of l thanks to the strategy 'RepeatId' which takes another strategy (here Remove) as an argument. */ System.out.println(`RepeatId(Remove()).visit(l)); } } tomuser@huggy$ tom RmDoubles.t && javac RmDoubles.java && java RmDoubles strlist("framboisier","eric","framboisier","remi","remi","framboisier","rene","bernard") strlist("framboisier","eric","remi","rene","bernard")

An expression evaluator --%strategy, InnerMostId `plus(val(2),var("x"),mult(val(3),val(4)),var("y"),val(5)); /* We choose to apply the rewrite system in an innermost way (aka. call by value). The InnermostId strategy does the job and stops when a fixpoint is reached.

Since the visit method of strategies returns a Visitable, we have to cast the result. */ Expr res = (Expr) `InnermostId(EvalExpr()).visit(e); System.out.println(e + "\n" + res); } } tomuser@huggy$ tom Eval.t && javac Eval.java && java Eval plus(val(2),var("x"),mult(val(3),val(4)),var("y"),val(5)) plus(var("x"),var("y"),val( 19))

Variable Collector --%strategy with mutable parameters Prop p = `forall("x", implies(implies(P(f(var("x"))), P(var("y"))),P(f(var("y")))));

System.out.println("free occurences of x: " + collectFreeOccurences("x",p));

System.out.println("free occurences of y: " + collectFreeOccurences("y",p)); System.out.println(l1 + "\n" + l2 + "\n" + l3); } } tomuser@huggy$ tom Sort.t && javac Sort.java && java Sort sorted (1,3,5,7,9) sorted (0,2,4,6,8) sorted (0,1,2,3,4,5,6,7,8,9,10) Sorted list revisited --advanced hooks Integers l = `sorted (7,5,3,1,9); System.out.println(l); } } tomuser@huggy$ tom Sort.t && javac Sort.java && java Sort 3 is greater than the head of sorted (9) 5 is greater than the head of sorted (3,9) 5 is greater than the head of sorted (9) 7 is greater than the head of sorted (3,5,9) 7 is greater than the head of sorted (5,9) 7 is greater than the head of sorted( 9) sorted (1,3,5,7,9) Guided Tour

Algebraic terms > Hooks > Mappings > Graphs

Tom Documentation

Guided Tour :: Tutorial :: Language Reference :: Tools Tom strategy. These term-graph rewriting rules can then be integrated in a more complex strategy using Tom strategy combinators. As a consequence, all Tom features are available for term-graphs.

Guided Tour

Algebraic terms > Hooks > Mappings > Graphs

Tom Documentation

Guided Tour :: Tutorial :: Language Reference :: Tools The %gom{ …} construct defines a data-structure, also called signature or algebraic data-type. This data-structure declares a sort (Nat) that has three operators (zero, suc, and plus). These operators are called constructors, because they are used to construct the data-structure. zero is a constant (arity 0), whereas the arities of suc and plus are respectively 1 and 2. Note that a name has to be given for each slot (pred for suc, and x1, x2 for plus).

Note: to use the code generated by a %gom {...}, an import statement has to be added: import main.peano.types.*;

The path corresponds to the name of the class (Main), followed by the name of the module (Peano), followed by types.*. These package names are in lowercase, even if the class name and the module name contain capitals.

Retrieving information in a data-structure

In addition to %gom and `, Tom provides a third construct: %match. Using the same program, we add a method evaluate(Nat n) and we modify the method run(): The %match construct is similar to switch/case in the sense that given a tree (n), the %match selects the first pattern that matches the tree, and executes the associated action.

By matching, we mean: giving values to variables to make the pattern equal to the subject. In our example n has the value plus(suc(zero()),suc(zero())). The first pattern does not match n, because the second subterm of n is not a zero(), but a suc(zero()). In this example, the second pattern matches n and gives the value suc(zero()) to x, and zero() to y.

When a pattern matches a subject, we say that the variables (x and y in our case) are instantiated. They can then be used in the action part (also called right-hand side).

Similarly, the second rules can be applied when the second subterm is rooted by a suc. In that case, x and y are instantiated.

The method evaluate defines the addition of two integers represented by Peano successors (i.e. zero and suc). The first case says that the addition of an integer with zero is evaluated into the integer itself. The second case builds a new term (rooted by suc) whose subterm (plus(x,y)) denotes the addition of x and y.

When executing the program we obtain: plus(suc(zero()),suc(zero())) suc(plus(suc(zero()),zero()))

Note: In a match construct, the variables should not be declared by the programmer. They are written without (), and their type is inferred. A variable introduced should be fresh: it should not be declared earlier in a wrapping block, either in Java, either in a %match construct. A Tom variable can be used in the corresponding action, but has to be introduced by a ` construct. Note that the scope of a back-quote expression is delimited by well-parenthesized sentences (`zero(), `suc(zero()), `suc(x)). The special case `x, corresponding to a variable alone, is also correct. To write complex expressions, extra parentheses can be added: `(x), `(x == y) for example.

Using rules to simplify expressions

In this section, we will show how to use the notion of rules to simplify expressions. Suppose that we want to simplify boolean expressions. It is frequent to define the relations between expressions using a set of simplification rules like the following: To encode such a simplification system, we have to implement a function that simplifies an expression until no more reduction can be performed. This can of course be done using functions defined in Java, combined with the %match constructs, but it is more convenient to use an algebraic construct that ensures that a rule is applied whenever a reduction is possible. For this purpose, the %gom construct provides a rule() construct where the left and the right-hand sides are terms. The previous simplification system can be defined as When programming large applications, it may be more convenient to introduce several classes that share a common data-structure. In that case, the %gom {...} construct could be avoided and a Gom file (Logic.gom for example) could be used instead: In the Tom program, %include { logic/Logic.tom } is necessary to include (like a copy and paste) the Logic.tom file generated by gom. The %include command is similar to the #include command provided by the C-preprocessor.

Not(a) → Nand(a,

Programming in Tom

In this section we present how Tom can be used to describe the abstract syntax and to implement an interpreter for a given language. We also give some tips and more information about the generated code.

When using %gom { ... }, the generated data-structure is particular: data are maximally shared. This technique, also known as hash-consing ensures that two identical subterms are implemented by the same objects. Therefore, the memory footprint is minimal and the equality-check can be done in constant time using the == construct (two terms are identical if the pointers are equal). As a consequence, a term is not mutable: once created, it cannot be modified.

Even if the generated API offers getters and setters for each defined slot (Bool getb1(), Bool getb2(), Bool setb1(Bool t) and Bool setb2(Bool t) for the which they are applied: t.setb1('True()) will return a copy of t where the first child is set to True(), but the previous t is not modified. There is no side-effect in a maximally shared setting.

In Tom, it is quite easy to quickly develop applications which manipulates trees. As an example, let us consider a tiny language composed of boolean expressions (True, False, And, Or, and Not), expressions (constant, variable, Plus, Mult, and Mod), and instructions (Skip, Print, ;, If, and While). The abstract syntax of this language can be described as `evalExpr(env,Plus(evalExpr(env,e1),evalExpr(env,e2))); } Mult(e1,e2) -> { return `evalExpr (env,Mult(evalExpr(env,e1),evalExpr(env,e2))); } Mod(e1,e2) -> { return `evalExpr (env,Mod(evalExpr(env,e1),evalExpr(env,e2))); }

x -> { return `x; } } throw new RuntimeException("should not be there: " + expr); } Note: the congruence rules are needed to enforce reductions in sub-expressions of Plus, Mult, and Mod.

We will see later how they can be avoided using the notion of strategy.

Similarly, the evaluation of boolean expressions can be implemented as follows: Note also the use of w@... that introduces a variable w (an alias). This variable can be used in the action part to avoid building the term While(b,i).

To play with the Pico language, we just have to initialize the environment (env), create programs (p1 and p2), and evaluate them (eval): Inst p1 = `Seq(Assign("a",Cst(1)) , Print(Var("a"))); System.out.println("p1: " + p1); eval(env,p1); Inst p2 = `Seq(Assign("i",Cst(0)), While(Not(Eq(Var("i"),Cst(10))), Seq(Print(Var("i")), Assign("i",Plus(Var("i"),Cst(1)))))); System.out.println("p2: " + p2); eval(env,p2); } Exercise: write a Pico program that computes prime numbers up to 100. This examples shows that pattern matching can be performed against built-in data-types. In this example, the %match construct is equivalent to a switch/case construct: as expected the first print statement is executed, but the second one is also executed since no break statement has been executed. " before 'l' and " + `after* + " after"); } } When applied to "Hello", there are two possible solutions for before* and after*:

Tutorial

we have found he before 'l' and lo after we have found hel before 'l' and o after

Let us suppose that we look for two consecutive 'l' anywhere in the matched expression.

This could be expressed by: %match(t) { concString(_*,'l','l',_*) -> { ... } } Since this syntax is error prone when looking for long/complex substrings, Tom provides an abbreviated notation: 'll':

%match(t) { concString(_*,'ll',_*) -> { ... } }
This notation is fully equivalent to the previous one.

String matching -continued

In the following, we consider the program: As illustrated previously, we can use variables to capture contexts. In fact, this mechanism is more general and we can use a variable anywhere to match something which is not statically known. The following pattern looks for two characters which are identical:

concString(_*,x,_*,x,_*) -> { System.out.println("x = " + `x); } Since list matching is not unitary, there may be several results. In this case, we obtain:

x = a x = b x = c
The second pattern looks for a character in a string which should begin with a 'a' and end with a 'c':

concString('a',_*,y,_*,'c') -> { System.out.println("y = " + `y); }

The results are:

y = b y = c y = a y = b
The third pattern look for the substring 'abc' anywhere in the string:

concString(C1*,'abc',C2*) -> { System.out.println("C1 = " + `C1*); } When the substring is found, the prefix C1* is:

C1 = C1 = abc
The last pattern illustrates the search of two identical substrings:

concString(_*,L*,_*,L*,_*) -> { if(`L*.length() > 0) { System.out.println("L = " + `L*); } }
The results are:

L = a L = ab L = abc L = b L = bc L = c
To look for a palindrome, you can use the following method:

List matching -Associative matching

As illustrated previously, Tom supports a generalized form of string matching, called list matching, also known as associative matching with neutral element. In Tom, some operators are special and do not have a fixed number of arguments. This intuitively corresponds to the idea of list where elements are stored in a given order. A list of elements may be written (a,b,c) or [a,b,c]. In Tom, it is written f(a(),b(),c()), where 'f' is this special operator. In some sense, 'f' is the name of the list. This allows to distinguish list of apples, from list of oranges for examples.

The definition of such operators can be done using Gom: is called a non-linear pattern since x appears twice). If there exists such two elements, the term f(X1*,x,X2*) is built (an x has been removed), and the removeDouble function is called recursively. When there is no such two elements, the pattern does not match, this means that the list does not contain any consecutive identical elements. Therefore, the instruction return l is executed and the function returns.

Similarly, a sorting algorithm can be implemented: if a list contains two elements in the wrong order, just swap them. This can be expressed as follows: Note: given a list l = f(b(),b(),a(),a()), there exists several ways to match the pattern.

public static L swapSort(L l) { %match(l) { f(X*,e1,Z*,e2,Y*) -> { if(`gt(e1, e2
In this case, there are 6 possibilities: Assuming that a < b, there are only 4 solutions (2, 3, 4, and 5 since e1 must be greater than e2) that can be used to apply the rule It becomes important to remind you how a rule is applied in Tom:

1. X*=f(), e1=b(), Z*=f(), e2=b(), Y*=f(a(),a()) 2. X*=f(), e1=b(), Z*=f(b()), e2=a(), Y*=f(a()) 3. X*=f(), e1=b
1. a rule whose pattern match is selected (in our case, there is only one rule), 2. then, for each solution of the matching problem (there are 6 solutions in our case), the right part is executed (i.e. the Java code). Let us suppose that Tom computes the solution 1. first (the order in which solutions are computed is not fixed and depends on the implementation). In that case, the test if('gt(e1,e2)) is evaluated. Since b() is not greater than b(), the return swapSort(...) is not performed. As specified in Section Match Construct, another solution is computed. Let us say 2.. In that case, the test becomes true and the function swapSort is called recursively. 3. when there is no more solution (i.e. this means that the list is already sorted), the control is transfered to the next pattern. Since there is no more pattern in our example, the return l is executed, which returns the sorted list.

The following code shows how to build a list and call the function defined previously. This results in sorted lists where elements only occur once.

Introduction to strategies

Elementary transformation

We call strategy an elementary transformation. Suppose that you want to transform the object a() into the object b(). You can of course use all the functionalities provided by Tom and Java. But in that case, you will certainly end in mixing the transformation (the piece of code that really replaces a() by b()) with the control (the Java part that is executed in order to perform the transformation).

The notion of strategy is a clear separation between control and transformation. In our case, we will define a strategy named Trans1 that only describes the transformation we have in mind: Therefore, if we consider the elementary strategy a ⇒b (which replaces a by b), we have the following results:

(a -> b)[a] = b (a -> b)[b] = failure (a -> b)[f(a)] = failure (Identity)[a] = a (Identity)[b] = b (Identity)[f(a)] = f(a) (Fail)[a] = failure

Basic combinators Composition

The sequential operator, Sequence(S1,S2), applies the strategy S1, and then the strategy

S2. It fails if either S1 fails, or S2 fails. (Sequence(a -> b, b -> c))[a] = c (Sequence(a -> b, c -> d))[a] = failure (Sequence(b -> c, a -> b))[a] = failure

Choice

The choice operator, Choice(S1,S2), applies the strategy S1. If the application S1 fails, it applies the strategy S2. Therefore, Choice(S1,S2) fails if both S1 and S2 fail.

(Choice(a -> b, b -> c))[a] = b (Choice(b -> c, a -> b))[a] = b (Choice(b -> c, c -> d))[a] = failure (Choice(b -> c, Identity))[a] = a

Not

The strategy Not(S), applies the strategy and fails when S succeeds. Otherwise, it succeeds and corresponds to the Identity.

(Not(a -> b))[a] = failure (Not(b -> c))[a] = a

Parameterized strategies

By combining basic combinators, more complex strategies can be defined. To make the definitions generic, parameters can be used. For example, we can define the two following strategies:

• Try(S) = Choice(S, Identity), which tries to apply S, but never fails

• Repeat(S) = Try(Sequence(S, Repeat(S))), which applies recursively S until it fails, and then returns the last unfailing result

(Try(b -> c))[a] = a (Repeat(a -> b))[a] = b (Repeat(Choice(b -> c, a -> b)))[a] = c (Repeat(b -> c))[a] = a

Traversal strategies

We consider two kinds of traversal strategy (All(S) and One(S)). The first one applies S to all subterms, whereas the second one applies S to only one subterm.

All

The application of the strategy All(S) to a term t applies S on each immediate subterm of t. The strategy All(S) fails if S fails on at least one immediate subterm.

(All(a -> b))[f(a)] = f(b) (All(a -> b))[g(a,a)] = g(b,b) (All(a -> b))[g(a,b)] = failure (All(a -> b))[a] = a (All(Try(a -> b)))[g(a,c)] = g(b,c)
Note: the application of All(S) to a constant never fails: it returns the constant itself.

One

The application of the strategy One(S) to a term t tries to apply S on an immediate subterm of t. The strategy One(S) succeeds if there is a subterm such that S can be applied. The subterms are tried from left to right.

(One(a -> b))[f(a)] = f(b) (One(a -> b))[g(a,a)] = g(b,a) (One(a -> b))[g(b,a)] = g(b,b) (One(a -> b))[a] = failure
Note: the application of One(S) to a constant always fails: there is no subterm such that S can be applied.

High level strategies

By combining the previously mentioned constructs, it becomes possible to define well know strategies:

BottomUp(S) = Sequence(All(BottomUp(S)), S)
TopDown(S) = Sequence(S, All(TopDown(S)))

OnceBottomUp(S) = Choice(One(OnceBottomUp(S)), S)

OnceTopDown(S) = Choice(S, One(OnceTopDown(S)))

Innermost(S) = Repeat(OnceBottomUp(S)) Outermost(S) = Repeat(OnceTopDown(S))

Strategies in practice

Let us consider again a Pico language whose syntax is a bit simpler than the one seen in section Level 1. Seq(Print(Var("i")), Let("i",Plus(Var("i"),Cst(1)),Var("i"))), Seq())); System.out.println("p4 = " + p4); System.out.println("opti(p4) = " + opti(p4)); } When executing this program, we obtain: p4 = Let("i",Cst(0),If(Neg(Eq(Var("i"),Cst(10))), ConsSeq(Print(Var("i")),ConsSeq (Let("i", Plus(Var("i"),Cst(1)),Var("i")),EmptySeq)),EmptySeq)) opti(p4) = Let("i",Cst(0),If(Neg(Eq(Var("i"),Cst(10))), ConsSeq(Print(Var("i")),ConsSeq (Let("i", Plus(Var("i"),Cst(1)),Var("i")),EmptySeq)),EmptySeq))

This does not correspond to the expected result, simply because the opti function performs an optimization when the expression starts with an If instruction. To get the expected behavior, we have to add congruence rules that will allow to apply the rule in subterms (one rule for each constructor):

public static Expr opti(Expr expr) { %match(expr) { If(Neg(b),i1,i2) -> { return `opti(If(b,i2,i1)); } // congruence rules Let(n,e1,e2) -> { return `Let(n,opti(e1),opti(e2)); } Seq(head,tail*) -> { return `Seq(opti(head),opti(tail*)); } If(b,i1,i2) -> { return `If(b,opti(i1),opti(i2)); } Print(e) -> { return `Print(e); } Plus(e1,e2) -> { return `Plus(e1,e2); }
x -> { return `x; } } throw new RuntimeException("strange term: " + expr); } Since this is not very convenient, we will show how the use of strategies can simplify this task.

Printing constants using a strategy

Let us start with a very simple task which consists in printing all the nodes that corresponds to a constant (Cst(_). To do that, we have to define an elementary strategy that is successful when it is applied on a node Cst(_):

%strategy stratPrintCst() extends Fail() { visit Expr { Cst(x) -> { System.out.println("cst: " + `x); } } } Note:
this strategy extends Fail. This means that its application leads to a failure when it cannot be applied. In our case, the strategy succeeds on nodes of the form Cst(x), and fails on all the others.

To traverse the program and print all Cst nodes, a TopDown strategy can be applied: This results in:

p4 = Let("i",Cst(0),If(Neg(Eq(Var("i"),Cst(10))),
ConsSeq(Print(Var("i")),ConsSeq(Let("i", Plus(Var("i"),Cst(1)),Var("i")),EmptySeq)),EmptySeq))

cst: 0 cst: 10 cst: 1

Combining elementary strategies

As a second exercise, we will try to write another strategy that performs the same task, but we will try to separate the strategy that looks for a constant from the strategy that prints a node. So, let us define these two strategies:

%strategy FindCst() extends Fail() { visit Expr { c@Cst(x) -> c } } %strategy PrintTree() extends Identity() { visit Expr { x -> { System.out.println(`x); } } }
Similarly to stratPrintCst, the strategy FindCst extends Fail. The goal of the PrintTree strategy is to print a node of sort Expr. By extending Identity, we specify the default behavior when the strategy is applied on a term of a different sort.

Note: we could have extended Fail and used Try(PrintTree()) instead.

To print the node Cst, we have to look for a Cst and print this node. This can be done by combining, using a Sequence, the two strategies FindCst and PrintTree: Note: in the second case, the nodes are printed using the toString() method generated by Gom.

Modifying a subterm

Here, we will try to rename all the variables from a given program: the name should be modified into _name.

To achieve this task, you can define a primitive strategy that performs the modification, and apply it using a strategy such as TopDown: The application of optimize to p4 results in:

Let("i",Cst(0),If(Neg(Eq(Var("_i"),Cst(10))), ConsSeq(Print(Var("_i")),ConsSeq(Let("i", Plus(Var("_i"),Cst(1)),Var("_i")),EmptySeq)),EmptySeq))

Suppose now that we want to print the intermediate steps: we do not want to perform all the replacements in one step, but for debugging purpose, we want to print the intermediate term after each application of the renaming rule.

The solution consists in combining the stratRenameVar strategy with the PrintTree strategy.

Note: you can try to implement it yourself before reading the solution A first solution consists in applying stratRenameVar using a OnceBottomUp strategy, and immediately apply PrintTree on the resulting term. This could be implemented as follows:

`Repeat(Sequence(OnceBottomUp(stratRenameVar()),PrintTree())).visit(expr);

Unfortunately, this results in:

Let("i",Cst(0),If(Neg(Eq(Var("_i"),Cst(10))),...

Let("i",Cst(0),If(Neg(Eq(Var("__i"),Cst(10))),...

Let("i",Cst(0),If(Neg(Eq(Var("___i"),Cst(10))),...

Let("i",Cst(0),If(Neg(Eq(Var("____i"),Cst(10))),...

Let("i",Cst(0),If(Neg(Eq(Var("_____i"),Cst(10))),... Let("i",Cst(0),If(Neg(Eq(Var("______i"),Cst(10))),... Let("i",Cst(0),If(Neg(Eq(Var("_______i"),Cst(10))),... Let("i",Cst(0),If(Neg(Eq(Var("________i"),Cst(10))),... Let("i",Cst(0),If(Neg(Eq(Var("_________i"),Cst(10))),... Let("i",Cst(0),If(Neg(Eq(Var("__________i"),Cst(10))),... Let("i",Cst(0),If(Neg(Eq(Var("___________i"),Cst(10))),... Let("i",Cst(0),If(Neg(Eq(Var("____________i"),Cst(10))),...

...

This is not the expected behavior! Why?

Simply because the renaming rule can be applied several times on a same variable. To fix this problem, we have to apply the renaming rule only if the considered variable has not already be renamed.

To know if a variable has been renamed, you just have to define an elementary strategy, called RenamedVar, that succeeds when the name of the variable starts with an underscore.

This can be easily implemented using string matching capabilities:

%strategy RenamedVar() extends Fail() { visit Expr { v@Var(('_',name*)) -> v } }
To finish our implementation, it is sufficient to apply stratRenameVar only when

RenamedVar fails, i.e., when Not(RenamedVar) succeeds.

`Repeat(Sequence( OnceBottomUp(Sequence(Not(RenamedVar()),stratRenameVar())), PrintTree())

).visit(expr);

This results in (layouts have been added to improve readability):

Let("i",Cst(0),If(Neg(Eq(Var("_i"),Cst(10))), ConsSeq(Print(Var("i")),ConsSeq(Let("i",

Re-implementing the tiny optimizer

Now that you know how to use strategies, it should be easy to implement the tiny optimizer seen in the beginning of section Level 3.

You just have to define the transformation rule and a strategy that will apply the rule in an innermost way: Let("i",Cst(0),If(Eq(Var("i"),Cst(10)),EmptySeq, ConsSeq(Print(Var("i")),ConsSeq (Let("i", Plus(Var("i"),Cst(1)),Var("i")),EmptySeq))))

%strategy OptIf() extends Fail() { visit Expr { If(Neg(b),i1,i2) -> If(b,i2 ,
Note: when programming with strategies, it is no longer necessary to implement a congruence rule for each constructor of the signature.

Anti pattern-matching

Tom patterns support the use of complements, called anti-patterns. In other words, it is possible to specify what you don't want to match. This is done via the '!' symbol, according to the grammar defined in the language reference. The anti-patterns can be also quite useful when used with lists. Imagine that you what to search for a list that doesn't contain a specific element. Without the use of anti-patterns, you would be forced to match with a variable instead of the element you don't want, and after that to perform a test in the action part to check the contents of the variable. For the signature defined above, if we are looking for a list that doesn't contain a(), using the anti-patterns we would write:

If we consider the

... Some more useful anti-patterns can be imagined in the case of lists:

...

Using constraints for more flexibility

Since version 2.6 of the language, a more modular syntax for %match and %strategy is proposed. Instead of having a pattern (or several for more subjects) as the left-hand side of rules in a %match or %strategy, now more complex conditions can be used.

Let's consider the following class that includes a Gom signature: In the above example, the first pattern checks that the subject contains two objects a(), and the second constraint verifies that the rest of the list doesn't contain any a().

Besides match constraints introduced with the symbol <<, we ca also have boolean constraints by using the following operators: >, >=, <, <=, == and !=. These can be used between any terms, and are trivially translated into host code (this means that the constraint term1 == term2 will correspond exactly to an if (term1 == term2) ... in the generated code). A simple example is the following one, which prints all the elements in a list of integers that are bigger than 5: ... (6,7,4,5,3,2,8,9 Note: When using a disjunction, the action is executed for each case that renders the disjunction valid (given of course that no return or break is used). For instance, the following code prints the messages here x=a() and here x=b():

...

Hand-written mappings

Up to now, we have considered examples where the implementation of data-types is either predefined (Xml case), or generated by a tool (Gom case). One interesting contribution of Tom is to be customizable. By defining a mapping between the signature formalism (%typeterm, %op, etc.) and the concrete implementation, it becomes possible to perform pattern matching against any data-structure.

Defining a simple mapping

In this section, we consider that we have a Java library for representing tree based data structures. On another side, to be able to use Tom, we consider the following abstract data-type:

%typeterm Nat %op Nat zero() %op Nat suc(Nat)
By doing so, we have defined a sort (Nat), and two operators (zero and suc). When defining a mapping, the goal consists in explaining to Tom how the considered abstract data-type is implemented, and how a term (over this signature) can be de-constructed.

For expository reasons, the ATerm [1] library is the Java library used to implement terms.

However, any other tree/term based library could have been used instead.

In order to define a correct mapping, we have to describe how the algebraic sort (Nat in our example) is implemented (by the ATermAppl class). This is done via the implement construct:

%typeterm Nat { implement { ATermAppl } }
The second part of the mapping definition consists in defining how the symbols (zero and suc) are represented in memory. This is done via the is_fsym construct: Given a term built over the ATerm library, it becomes possible to perform pattern matching as previously explained.

%op Nat zero() { is_fsym(t) { t.

Using backquote constructs

When using the backquote construct ('suc(suc(zero)) for example), Tom has to know how to build a term in memory. For this purpose, we consider an extension of the signature definition formalism: the make construct. In this example, we illustrate another possibility offered by Tom: being able to know whether a term is rooted by a symbol without explicitly representing this symbol. The is_fsym(t) construct should return true when the term t is rooted by the algebraic operator we are currently defining. In this example, we say that the term t is rooted by the symbol person when the object t is implemented by an instance of the class Person. By doing so, we do not explicitly represent the symbol person, even if it could have been done via the reflective capabilities of Java (by using Person.getClass() for example).

Using list-matching

In this section, we show how to describe a mapping for associative operators.

%typeterm TomList { implement { ArrayList } equals(l1,l2) { l1.equals(l2) } }
Assuming that the sort Element is already defined, we can use the %oparray construct to define an associative operator. We also have to explain to Tom how to compute the size of a list, and how to access a given element. This is done via get_size and get_element constructs:

%oparray TomList conc( Element* ) { is_fsym(t) { t instanceof ArrayList } get_element(l,n) { (ATermAppl)l.get(n) } get_size(l) { l.size() } make_empty(n) { myEmpty(n) }
make_append(e,l) { myAdd(e,(ArrayList)l) } } This construct is similar to %op except that additional information have to be given: how to build an empty list (make_empty), and how to add an element to a given list (make_append).

The auxiliary Java functions are defined as follows: Tom offers another similar construct %oplist to map an associative operator to a linked-list based implementation. When using the ATerm library for example, a possible implementation could be: The problem consists in implementing such a verification tool in Tom and Java.

%typeterm TomTerm { implement { aterm.ATermAppl } equals(t1, t2) { t1==t2 } } %typeterm TomList { implement { ATermList } equals(l1,l2) { l1==l2 } } %oplist TomList conc( TomTerm* ) { is_fsym(t) { t instanceof

Loading Xml documents

The first part of the program declares imports, and defines the main and the run methods. This mapping has to be initialized in the following way:

• the import of tom.library.adt.tnode.* and tom.library.adt.tnode.types.* defines the sorts TNode and TNodeList and allows us to build objects over these two sorts.

• the %include{ TNode.tom } Tom construct is similar to the #include C preprocessor construct. In this case, it imports the definition of Tom algebraic constructors needed to manipulate Xml documents.

In complement to Tom, we provide a runtime library which contains several methods to manipulate Xml documents. In particular, we provide the XmlTools class (defined in the tom.library.xml.* package).

The run method takes two filenames as arguments, reads the associated files and convert their Xml content into TNode terms (using the convertXMLToATerm function).

The getDataGroup function is used to retrieve a <DATA></DATA> node in the considered Xml document. Note that getDocElem is first applied to Xml documents in order to consider subterms of the DocumentNode element. Then, the compareDataGroup function is used to check that the client's policy is compatible with the server's policy. The content of these functions is detailed in the next sections.

Retrieving information

Given an Xml subtree, the problem consists in extracting a <DATA-GROUP></DATA-GROUP> node. For expository reasons, we first consider that such a <DATA-GROUP></DATA-GROUP> node can only appear at two different specific places: one for the client's definition and one for the server's definition.

Thus, in the Tom program we naturally consider two cases:

Comparing two Xml subtrees

Given two <DATA-GROUP></DATA-GROUP> nodes, the problem consists in checking that all <DATA></DATA> nodes from the first tree also appear in the second one. This can be easily implemented by the following couple of functions: Given the string refclient we look for a <DATA></DATA> subtree containing a ref attribute with exactly the same string. Since it is not possible to use an instantiated variable in a pattern (something like <DATA ref=refclient>...</DATA>, we have to introduce a fresh variable reftext and check in a condition that this variable is equal to refclient.

This is done via a Java condition (the if clause): the action part (return true;) is executed only when the condition is satisfied, and clearly it will end the method. If the condition is not satisfied, then the next <DATA></DATA> subtree is searched. It is exactly the case of a switch statement, when the action part is not exited by a return, break or goto, and the control flow is transferred to the next matching solution or the next matching pattern.

If no such subtree exists, this means that the two policies are not compatible and false is returned.

Retrieving information using strategies

The Tom strategy library provides a set of generic operators in order to perform various kinds of traversal over a term. This is useful when searching a pattern somewhere in a term, at any position. As the Xml documents are seen by Tom as terms, the strategy library is also valid when dealing with Xml. The problem consists in sorting this document according to different criteria (age or first-name for example).

In

Loading Xml documents

The first part of the program declares imports, and defines the main method.

}

The mapping has to be initialized in the following ways:

• the import of org.w3c.dom.* and javax.xml.* packages in order to use the DOM library.

• the %include{ dom.tom } construct imports the definition of Tom algebraic constructors needed to manipulate DOM objects.

• the dom variable has to be instantiated. This variable corresponds to the notion of Document in the DOM terminology.

Comparing two nodes

In order to implement a sorting algorithm, we need to know how to compare two elements.

The following function takes two Xml documents in argument and compares their attribute

Age, using the string comparison operator compareTo. This feature, combined with the implicit notation, is such that <Person Age=a1></Person> will match any Xml node headed by Person which contains the attribute Age. This Xml node may contain several sub-nodes, but they will not be stored in any variable.

Sorting a list of nodes

In this section we use a swap sort algorithm which consists in finding two elements that are not in the correct order. Once they are found, they are swapped before calling the algorithm recursively. When no two such elements exist, this means that the list is sorted. Note that the action part is guarded by a condition (if(compare(p1,p2) > 0)). This means that return sort(...) is executed only when two bad-ordered elements are found. When p1 and p2 are correctly ordered, the matching procedure continues and extracts another couple p1 and p2. As mentioned in the Tom Pattern part, when Tom cannot find two elements p1 and p2 such that the condition is satisfied (the list is sorted), the return sort(...) statement is not executed and the control flow is transferred to the following statement: return subject;

As mentioned previously, when two elements have to be swapped, a new list is built. This done via the ''' (backquote) construct. This construct, used before to retrieve instantiated

Sorting by side effect

In the previous section, we considered a sorting algorithm expressed in a pure functional programming style: when two elements have to be swapped, a new list is built and returned.

In the following example, we exploit OO-style of the DOM library and perform a swap in place: the list is updated by swapping two elements (with side effect):

private static void sort(Node subject) { %match(subject) { r @ <_>p1@<_ Age=a1></_> p2@<_ Age=a2></_></_> -> { if(`a1.compareTo(`a2) > 0) { `r.replaceChild(`p2.cloneNode(true),`p1);

Tom constructs

A Tom program is a host language program (namely C, Java, or Caml) extended by several new constructs such as %match, %strategy, %include, %gom, or backquote. Tom is a multi-language compiler, and therefore its syntax depends on the host language syntax. But for simplicity, we only present the syntax of its constructs and explain how they can be integrated into the host language.

Using Java as a host-language, the following Tom program is correct: Syntax of a Tom program:

public class
Tom ::= BlockList BlockList ::= ( MatchConstruct | StrategyConstruct | BackQuoteTerm | IncludeConstruct | GomConstruct | TypeTerm | Operator | OperatorList | OperatorArray | '{' BlockList '}'
)*

• MatchConstruct is translated into a list of instructions. This construct may appear anywhere a list of instructions is valid in the host language.

• StrategyConstruct is translated into a class definition. Since it is translated into a class, this construct is valid only for Java. • BackQuoteTerm is translated into a function call.

• IncludeConstruct is replaced by the content of the file referenced by the construct. Tom looks for include files in: ./packageName/, $TOM_HOME/share/jtom/ and <path>, where <path> is specified by option: --import <path>. If the file contains some Tom constructs, they are expanded.

• GomConstruct allows to define a Gom grammar. This construct is replaced by the content of the generated mapping. See Section Gom Construct and Chapter Documentation:Gom for more details.

• TypeTerm, as well as Operator, OperatorList, and OperatorArray are replaced by some functions definitions.

Match construct

The %match construct (MatchConstruct) is one of the main contributions of Tom. This construct can be seen as an extension of the SwitchCase construct in C or Java, except that patterns are no longer restricted to constants (chars or integers). Given an object (the subject) and a list of patterns, our goal is to find the first pattern that matches the subjects (i.e. that has a compatible shape). More formally, a pattern is a term built over variables and constructors. The latter ones describe the shape of the pattern, whereas the variables are holes that can be instantiated to capture a value. When we consider the term f(a(),g(b())), it has to be viewed as a tree based data-structure with f as a root and a() the first child. Similarly, b() is the unique child of g, which is the second child of the root f . We say that the pattern f(x,y) matches this term (called subject), because we can give values to

x and y such that the pattern and the subject become equal: we just have to assign a() to x and g(b()) to y. Finding this assignment is called matching and instantiating. This is exactly what Tom is supposed to do. A pattern may of course contain subterms. Therefore, f(x,g(b())) or f(a(),g(y)) are valid patterns which match against the subject.

Assuming that s is a Java variable, referencing a term (the tree based object f(a(),g(b())) for example), the following Tom construct is valid: A MatchConstruct is composed of two parts:

%match(s) { f(a(),g(y)) -> { /*
• a list of subjects (the arguments of %match),

• a list of PatternAction: this is a list of pairs (pattern,action), where an action is a set of host language instructions which is executed each time a pattern matches the subjects.

Since version 2.6 of the language, an additional syntax, based on constraints, is proposed.

In this case, the MatchConstruct can be simply seen as a list of pairs (constraint,action) corresponding to ConstraintAction from the above syntax. For instance, the example we presented before can now be written: Note: Constraints built using an operator are trivially translated into host code. For instance, the constraint x == g(a()) ... is translated into the Java code if (x == g(a())) { ...

}

For expository reasons, we consider that a %match construct is evaluated in the following way:

• given a list of subjects (they correspond to objects only composed of constructors, therefore without variables, usually called ground terms), the execution control is transferred to the first PatternAction whose patterns match the list of ground terms (in the case constraints are used, the execution control is transferred to the first ConstraintAction whose Constraint is evaluated to true).

Note: since version 2.4, a subject is no longer restricted to a host language variable. A Tom term built upon variables, constructors and host-language functions can be used. Note also that the sort (the type of the subjects)

is now optional -it is inferred from the type of the patterns.

• given such a PatternAction (respectively ConstraintAction), its variables are instantiated and the associated semantic action is executed. The instantiated variables are bound in the underlying host-language, and thus can be used in the action part. • if the execution control is transferred outside the %match instruction (by a goto, break or return for example), the matching process is finished. Otherwise, the execution control is transferred to the next PatternAction whose patterns match the list of ground terms (respectively to the next ConstraintAction whose Constraint evaluates to true).

• when there is no more PatternAction whose patterns match the list of subjects (respectively no more ConstraintAction whose Constraint evaluates to true), the %match instruction is finished, and the execution control is transferred to the next instruction.

The semantics of a match construct may remind the switch/case construct. However, there is a big difference. For instance, in Tom we can have patterns (list-patterns) that can match in several ways a subject. Informally, when considering the subject conc(a(),b(),c()), and the pattern conc(_ * ,x,_ * ), there are three possible match for this problem: either x=a(), either x=b(), either x=c(). Note that _ * is a special hole which can capture any sublist of conc(…).

The list-matching is also known as associative matching. Besides this, some other matching theories are supported in Tom.

When taking this new possibility into account, the evaluation of a %match construct gets a little bit more complex:

• given a PatternAction whose patterns match the list of ground terms (or a ConstraintAction whose Constraint is evaluated to true), the list of variables is instantiated and the associated semantic action is executed.

• if the execution control is not transferred outside the %match instruction, in addition to the previous explanations, if the considered matching theory may return several matches, for each match, the free variables are instantiated and the associated semantic action is executed. This means that the same action may be executed several times, but in a different context: i.e. the variables have different instantiations.

• when all matches have been computed (there is at most one match in the syntactic theory, i.e. when no special theory, as associativity for instance, is associated to the symbols used in the patterns), the execution control is transferred to the next PatternAction whose patterns match the list of ground terms (respectively to the next ConstraintAction whose Constraint evaluates to true).

• as before, when there is no more PatternAction whose patterns match the list of subject (or respectively no ConstraintAction whose Constraint evaluates to true), the %match instruction is finished, and the execution control is transferred to the next instruction.

As mentioned in the BNF-syntax, a label may be attached to a pattern. In that case, in C and Java, it becomes possible to exit from the current PatternAction (using a goto or a break), without exiting from the whole %match construct. The control is transferred to the next pattern which matches the subjects (respectively to the next constraint). This feature is useful to exit from a complex associative-matching for which, for any reason, we are no longer interested in getting other solutions.

Note: the behavior is not determined if inside an action the subjects of the %match instruction under evaluation are modified.

When using the new syntax based on constraints, there are several restrictions that are imposed by the compiler (an error is generated if they are not respected):

• no circular references among variables are allowed. For instance, something like x << x will generate an error. This verification works even when the cycles are less evident, like for instance for the following constraint: f(g(x),a()) << y && f(b(),y) << z && g(f(z,c())) << x.

• when using disjunctions, all the variables that are used in the action have to be found in each member of the disjunction (for ensuring that no non-instantiated variable is used in the action). For instance, using the following ConstraintAction generates an error: x << s1 || y << s2 -> { /* code that uses y */ }

Tom pattern

As we can imagine, the behavior of a %match construct strongly depends on the patterns which are involved. The formalism which defines the syntax of a pattern is also an essential component of Tom. But because there exist several ways to define patterns with equivalent behavior, its formal definition is not so simple. Although, the different shortcuts help the programmer to simplify the definitions of patterns.

Informally, a pattern is a term built with constructors and variables (please note that x denotes a variable, whereas a() is a constructor). A variable can also be anonymous, and it is denoted by _. Let's look at some examples of patterns: x, a(), f(a()), g(a(),x), or h(a(),_,x). When a pattern matches a subject, it may be useful to keep a reference to a matched subterm. The annotation mechanism (z@g(y) for example) can be used for this purpose. Thus, considering the matching between the pattern f(x,z@g(y)) and the subject f(a(),g(h(b()))), y is instantiated by h(b()), and z is instantiated by g(h(b())). This can be useful in C, to free the memory for example.

When identical actions have to be performed for a set of patterns which share a common structure, the disjunction of symbols may be used: pattern (f|g)(a()) is equivalent to the set {f(a()), g(a())}. The disjunction of symbols may also be used in subterms, like in h( (f|g)(x) ).

More formally, a Tom pattern and a Tom term has the following syntax: A pattern is a term which could contain variables. When matching a pattern against a subject (a ground term), these variables are instantiated by the matching procedure (generated by Tom). In Tom, the variables do not have to be declared: their type is inferred automatically, depending on the context in which they appear.

As described previously, Tom offers several mechanisms to simplify the definition of a pattern:

• standard notation: a pattern can be defined using a classical prefix term notation. To make a distinction between variables and constants, the latter have to be written with explicit parentheses, like x(). In this case, the corresponding Tom operator (%op x())

should have been declared. When omitting parentheses, like x, this denotes a variable.

• unnamed variables: the _ notation denotes an anonymous variable. It can be used everywhere a variable name can be used. It is useful when the instance of the variable does not need to be used. Similarly, the _* notation can be used to denote an anonymous list-variable. This last notation can improve the efficiency of list-matching because the instances of anonymous list-variables do not need to be built. • annotated variable: the @ operator allows to give a variable name to a subterm. In f(x@g(_)) for example, x is a variable that will be instantiated by the instance of the subterm g(_). The variable x can then be used as any other variable.

• implicit notation: as explained below, the %op operator forces to give name to arguments.

Assuming that the operator f has two arguments, named arg1 and arg2, then we can write the pattern f[arg1=a()] which is equivalent to f(a(),_). This notation is interesting mostly when using constructors with many subterms. Besides that, using this notation can avoid changing the patterns when the signature slightly changes (the order of the arguments, adding a new argument etc).

• unnamed list operator: it is often the case that given a list-sort, only one list-operator is defined. In this case, when there is no ambiguity, the name of the operator can be omitted. Considering the conc list-operator for example (see %oplist and %oparray below), to improve the readability, the pattern conc(_*,x,_*) can be written (_*,x,_*).

This feature is particularly useful in the XML notation introduced in the following.

• symbol disjunction notation: to factorize the definition of pattern which have common subterms, it is possible to describe a family of patterns using a disjunction of symbols.

The pattern (f|g)(a(),b()) corresponds to the disjunction f(a(),b()) or g(a(),b()).

To be allowed in a disjunction (in standard notation), the constructors should have the same signature (arity, domain and codomain).

In practice, it is usually better to use the disjunction notation with the implicit notation Tom offers: ((f|g)[arg1=a()]). In that case, the signatures of symbols do not have to be identical: only involved slots have to be common (same names and types). Thus, the pattern (f|g)[arg1=a()] is correct, even if g has more slots than f: it only has to have the slot arg1, with the same sort.

Note: the disjunction of symbol can also be used in Xml notation: <(A|B)>...</(A|B)>.

The use of '?' after a list operator enables real associative with neutral elements (AU) matchings. By using conc? for example, we simply specify that the subject may not start with a conc symbol. For instance, the following code would produce the output matched, because x and respectively y can be instantiated with the neutral element of conc (please see the documentation on Gom for further details about specifying symbols' type and their neutral elements).

L l = `a(); %match(l) { conc?(x*,y*) -> { System.out.println("matched"); } } Note that without the use of '?', the subject must start with a conc in order to have a match.

Note: since version 2.5 we can use, inside a list, a subpattern that also denotes a list; moreover, this subpattern can be annotated. For instance, patterns like conc(_*,p@conc(a(),_*,b()),_*) are now valid.

Tom anti-pattern

The notion of anti-pattern offers more expressive power by allowing complement constructs: a pattern can describe what should not be in the matched subject.

The notion of complement is introduced by the symbol '!', as illustrated by the following grammar fragment:

PlainPattern ::= ['!'] VariableName | ['!'] HeadSymbolList ( ExplicitTermList | ImplicitPairList ) | ...
The semantics of anti-patterns can be best understood when regarding them as complements. For example, a pattern like car[color=blue()] will match all the blue cars.

If we add an '!' symbol, the anti-pattern !car[color=blue()] will match everything that is not a blue car, i.e all objects that are not cars or the cars that have a color different from blue. The grammar allows also car[color=!blue()] -matches all cars that are not blue, or

!car[color=!blue()] -either everything that is not a car, or a blue car.

Using the non-linearity combined with anti-patterns allows to express interesting searches also. For example, car[interiorColor=x,exteriorColor=x] will match the cars that have the same interior and exterior color. By using the anti-pattern car[interiorColor=x,exteriorColor=!x], the result is as one would expect: it will match all the cars with different interior -exterior colors.

It is also possible to use the anti-patterns in list constructions. Please refer to the tutorial for more examples.

Note: The use of annotations (@) is forbidden bellow a '!' symbol and is prevented by a compilation error. This is due to the fact that what is under this symbol generally will not match, therefore it cannot be used in the action part of the rules. You will also get an error if you try to put '!' before an '_' or '_*' because a construct like '!_' in a pattern will never match anything, therefore it is useless.

Backquote construct

Backquote construct (`) can be used to build an algebraic term or to retrieve the value of a Tom variable (a variable instantiated by pattern-matching).

BackQuoteTerm ::= ['`'] CompositeTerm
The syntax of CompositeTerm is not fixed since it depends on the underlying language.

However, CompositeTerm should be of the following form:

• Name: to denote a {{tom}} variable

• Name'*': to denote a {{tom}} list-variable

• Name( ... ): to build a prefix term • ( ... ): to build an expression

• xml( ... ): to build an Xml term

In general, it is sufficient to add a backquote before the term you want to build to have the desired behavior. The execution of `f(g(a())) will build the term f(g(a)), assuming that f, g, and a are Tom operators. Suppose now that g is no longer a constructor but a function of the host-language. The construction `f(g(a())) is still valid, but the semantics is the following: the constant a is built, then the function g is called, and the returned result is put under the constructor f. Therefore, the result of g must be a correct term, which belongs to the right type (i.e. the domain of f).

To simplify the interaction with the host-language, it is also possible to use "unknown symbols" like f(x.g()) or f(1+x). The scope of the backquote construct is determined by the scope of the most external enclosing braces, except in two case: `x and `x* which allow you to use variables instantiated by the pattern part. In that case the scope is limited to the length of the variable name, eventually extended by the ''*''. Sometimes, when writing complex expression like if(`x==`y || `x==`z), it can be useful to introduce extra braces (if( `(x==y || x==z) )) in order to extend the scope of the backquote.

Note: parsing backquote expressions is quite difficult. In some cases, Tom does not manage to parse correctly the expression:

• identifier immediatly followed by a closing brace: {`x} for instance. Solution: use extra parenthesis: {`(x)},

• spaces in backquotes expressions are not preserved: `f(new Apple()) generates a code that looks like make_f(newApple()). Workaround: introduce an intermediate variable to store the object

• confusion between star and multiplication: `x*y is interpreted as `x* followed by y (instead of x times y). Solution: introduce extra spaces `x * y.

Meta-quote construct

Tom provides the construct '%[' … ']%' that allows to build formatted strings without the need to encode special characters such as tabulations and carriage returns as it is usually done in Java. For example, to build a string containing the HelloWorld program, one can Even if the contents of the meta-quote construct is a formatted string, it is required that this string contains correctly balanced braces.

Note: the expression between two '@' can contain Tom constructs, like backquote constructs for example.

Note: use '@@' to insert the character '@' Tom signature constructs (*)

Sort definition constructs

To define the mapping between the algebraic constructors and their concrete implementation, Tom provides a signature-mapping mechanism composed of several constructs. In addition to predefined mapping for usual builtin sorts (int, long, double, boolean, string, and char), all other algebraic sorts have to be declared using the %typeterm construct.

To use predefined sorts (in a '%match' construct or in the definition of an algebraic operator), it is sufficient to use the '%include' construct (%include { int.tom } for example).

When defining a new type with the '%typeterm' construct, some information has to be provided:

• the 'implement' construct describes how the new type is implemented. The host language part written between braces ('{' and '}') is never parsed. It is used by the compiler to declare some functions and variables.

• the 'is_sort(t)' construct specifies how to check the sort of an object of this type (in Java this is usually done with 'instanceof'). It is only required when using this type in a '%match' construct.

• the 'equals(t1,t2)' construct corresponds to a predicate (parameterized by two term variables). This predicate should return true if the terms are "equal". The true value should correspond to the builtin true value of the considered host language. This last optional predicate is used to compare builtin values and to compile non-linear left-hand sides.

Given a Java class Person we can define an algebraic mapping for this class:

%typeterm TomPerson { implement { Person } is_sort(t) { t instanceof Person } equals(t1,t2) { t1.equals(t2) } }
Here, we assume that the method equals implements a comparison function over instances of Person. Note that we used TomPerson to make a clear distinction between algebraic sorts (defined in Tom) and implementation sorts (defined in Java, via the use of classes). In practice, we usually use the same name to denote both the algebraic sort and the implementation sort. Note: since version 2.6, the variables used in the host-code may be prefixed by a '$' sign. This allows the compiler to inline the definition, making the code often smaller and more efficient. For example:

%typeterm TomPerson { implement { Person } is_sort(t) { $t instanceof Person } equals(t1,t2) { $t1.equals($t2) } } Note: '$' should not be used if a backquote construct is used in a mapping

Constructor definition constructs

Once algebraic sorts are declared (using '%typeterm'), Tom provides a mechanism to define signatures for constructors of these sorts using '%op', '%oplist' or '%oparray'

constructs. When defining a new symbol with the '%op' construct, the user should specify the name of the operator, its codomain, and its domain. The later one is defined by a list of pairs (slot-name, sort).

Let us consider again the class Person, and let us suppose that an instance of Person has two fields (name and age), we can define the following operator:

%op TomPerson person(name:String, age:int)

In this example, the algebraic operator person has two slots (name and age) respectively of sorts String and int, where String and int are pre-defined sorts.

In addition to the signature of an operator, several auxiliary functions have to be defined:

• The 'is_fsym(t)' construct is used to check if a term 't' is rooted by the considered symbol. The true value should correspond to the builtin true value of the considered host language (true in Java or Caml, and something different from 0 in C for example).

• The 'make(t1,...,tn)' construct is parameterized by several variables (i.e. that should correspond to the arity of the symbol). A call to this 'make' function should return a term rooted by the considered symbol, where each subterm correspond to the terms given in arguments to the function. When defining a constant (i.e. an operator without argument, make can be defined without braces: make { ... }).

• The 'get_slot(slotName,t)' construct has to be defined for all slots of the signature.

The implementation of these constructs should be such that the corresponding subterm is returned. When defining a new symbol with the '%oplist' construct, the user has to specify how the symbol is implemented. In addition, the user has to specify how a list can be built and accessed:

• the 'make_empty()' construct should return an empty list.

• the 'make_insert(e,l)' construct corresponds to a function parameterized by a list variable and a term variable. This function should return a new list l' where the element e has been inserted at the head of the list l (i.e. 'equals(get_head(l'),e)' and 'equals(get_tail(l'),l)' should be true).

• the 'get_head(l)' function is parameterized by a list variable and should return the first element of the considered list.

• the 'get_tail(l)' function is parameterized by a list variable and should return the tail of the considered list.

• the 'is_empty(l)' constructs corresponds to a predicate parameterized by a list variable. This predicate should return true if the considered list contains no element.

Similarly, when defining a new symbol with the '%oparray' construct, the user has to specify how the symbol is implemented, how an array can be built, and accessed:

• the 'make_empty(n)' construct should return a list such that n successive 'make_append(e,l)' can be made.

• the 'make_append(e,l)' construct corresponds to a function parameterized by a list variable and a term variable.

Warning: This function should return a list l' such that the element e is at the end of l.

• the 'get_element(l,n)' construct is parameterized by a list variable and an integer.

This should correspond to a function that return the n-th element of the considered list l.

• the 'get_size(l)' constructs corresponds to a function that returns the size of the considered list (i.e. the number of elements of the list). The size of an empty list is 0.

The '%oplist' or '%oparray' is complex but not difficult to use. Let us consider the ArrayList Java class, and let us define a Tom mapping over this data-structure. The first thing to do consists in defining the sort for the elements and the sort for the list-structure:

It allows to define a Gom signature (for more details about Gom see Chapter Gom). The Gom compiler is called on the GomGrammar, and the construct is replaced by the produced Tom mapping. The OptionString is composed by a list of command line options to pass to the underlying Gom compiler, as described in Section Using Gom.

XML pattern

To deal with XML documents, the XML notation can be used (<A><B attribute="name"/></A> for example).

When manipulating XML documents, we distinguish two main kinds of operations:

retrieving information and transforming a document. Tom provides three different XML notations that ought to simplify the definition of patterns: the "standard " and the "implicit"

XML notations are used to define compact (but incomplete) patterns. This notation is well suited to retrieve information. The "explicit" XML notation is used to precisely describe an XML pattern and all the variables that have to be instantiated. This notation is particularly well suited to perform XML transformation since it allows the programmer to precisely describe how variables have to be instantiated.

To make the XML notation understandable, we have to explain how XML documents are handled by Tom. To each XML document corresponds a DOM (Document Object Model) representation. In Tom, we have defined a mapping from DOM sorts to abstract algebraic sorts: TNode and TNodeList, which correspond respectively to Node and NodeList, defined by the Java DOM implementation.

Thus, a Node object becomes a ternary operator Element whose first subterm is the name of the XML node, the second subterm is a list of attributes and the third subterm is a list of subterms (which correspond to XML sub-elements). The second and the third elements are terms of sort TNodeList (because they are implemented by NodeList objects in DOM).

Thus, when considering the <A></A> XML document, the corresponding algebraic term is The basic functionality of Gom is to provide a tree implementation in Java corresponding to an algebraic specification. The syntax is inspired from the algebraic type definition of ML languages. Gom generates an efficient code which ensures maximal sharing.

Element("A",[],[]), where
To maintain the terms in a preferred canonical form, Gom provides an original hooks mechanism comparable to "private types" of Caml, or "smart constructors" of Haskell.

The tree implementations Gom generates are characterized by strong typing, immutability (there is no way to manipulate them with side-effects), maximal subterm sharing and the ability to be used with strategies.

Gom syntax

Gom provides a syntax to concisely define abstract syntax tree. Each Gom file consists in the definition of one or more modules. In each module we define sorts, and operators for the sorts. Additionally, we can define hooks to modify the default behavior of a constructor operator.

Example of signature

The syntax of Gom is quite simple and can be used to define many-sorted abstract-datatypes. The module section defines the name of the signature. The imports section defines the name of the imported signatures. The abstract syntax part defines the operators with their signature. For each argument, a sort and a name (called slot-name)

has to be given. The definition of a signature in Gom has several restrictions:

• there is no overloading: two operators cannot have the same name • for a given operator, all slot-names must be different

• if two slots have the same slot-name, they must belong to the same sort. In the previous example, Eq, Add, and Mul can have a slot called lhs of sort Expr. But, Id and Nat cannot have a same slot named value, since their sort are not identical (the slots are respectively of sorts String and int for Id and Nat).

Builtin sorts and operators

Gom supports several builtin sorts, that may be used as sort for new operators slots. To each of these builtin sorts corresponds a Java type. Native data types from Java can be used as builtin fields, as well as ATerm and ATermList structures. To use one of these builtin types in a Gom specification, it is required to add an import for the corresponding builtin. It is not possible to define a new operator whose codomain is one of the builtin sorts, since those sorts are defined in another module.

Note: to be able to use a builtin sort, it is necessary to declare the import of the corresponding module (int or

String) in the Imports section.

External Gom modules may be imported in a Gom specification, by adding the name of the module to import in the 'imports' section. Once a module imported, it is possible to use any of the sorts this module declares or imports itself as type for a new operator slot.

Adding new operators to an imported sort is however not allowed.

Grammar

Operator ::= '>' | '>=' |'<' |'<=' |'==' | '!='

Using Gom with Tom

A first solution to combine Gom with Tom is to use Gom as a standalone tool, using the command line tool or the ant task.

In that case, the module name of the Gom specification and the package option determine where the files are generated. To make things correct, it is sufficient to import the generated Java classes, as well as the generated Tom file. In the case of a Gom module

}

Note that the Java code is generated in a package that corresponds to the current package, followed by the class-name and the module-name. This allows to define the same module in several classes, and avoid name clashes.

Hooks

Gom provides hooks that allow to define properties of the data-structure, in particular canonical forms for the terms in the signature in an algebraic way.

Algebraic rules

The 'rules' hook defines a set of conditional rewrite rules over the current module signature. Those rules are applied systematically using a leftmost-innermost reduction strategy. Thus, the only terms that can be produced and manipulated in the Tom program are normal with respect to the defined system. Note: it is possible to define rules on a variadic symbol. However, due to the leftmost-innermost rule application strategy, using a list variable at the left of a pattern is usually not needed, and may result in an inefficient procedure.

Hooks to alter the creation operations

Hooks may be used to specify how operators should be created. 'make', 'make_empty' and 'make_insert' hooks are altering the creation operations for respectively algebraic, neutral element (empty variadic) and variadic operators. 'make_insert' is simply a derivative case of 'make', with two arguments, for variadic operators.

The hook operation type is followed by a list of arguments name between '()'. The creation operation takes those arguments in order to build a new instance of the operator.

Thus, the arguments number has to match the slot number of the operator definition, and types are inferred from this definition.

Then the body of the hook definition is composed of Java and Tom code. The Tom code is compiled using the mapping definition for the current module, and thus allows to build and match terms from the current module. This code can also use the realMake function, which

List theory hooks

In order to ease the use of variadic operators with the same domain and co-domain, Gom does provide hooks that enforce a particular canonical form for lists.

• FL, activated with <op>:FL() {}, ensures that structures containing the operator <op> are left to right comb, with an empty <op>() at the right. This constitutes a particular form of associative with neutral element canonical form, with a restriction on the application of the neutral rules. This corresponds to the generation of the following normalisation rules: make(Empty(),tail) -> tail make(Cons(h,t),tail) -> make(h,make(t,tail)) make(head,tail) -> make(head,make(tail,Empty)) if tail!=Empty and tail!=Cons

• Free, activated with <op>:Free() {}, ensures the variadic symbol remains free, i.e.

deactivates the default FL hook.

• AU, activated with <op>:AU() {}, ensures that structures containing the <op> operator are left to right comb, and that neutral elements are removed. It is possible to specify an alternate neutral element to the associative with neutral theory, using <op>:AU() {`<elem>()}, where <elem> is a term in the signature. This will generate the following normalisation rules: make(Empty(),tail) -> tail make(head,Empty()) -> head make(Cons(h,t),tail) -> make(h,make(t,tail))

• ACU is similar to AU, except that it also ensures elements in the left to right comb are sorted using the builtin compareTo function.

make(Empty(),tail) -> tail make(head,Empty()) -> head make(Cons(h,t),tail) -> make(h,make(t,tail)) make(head,Cons(h,t))

-> make(head,Cons(h,t)) if head < h make(head,Cons(h,t)) -> make(h,make(head,t)) if head >= h

If you do not define any hook of the form AU, ACU, FL, Free, or rules, the FL hook will be automatically declared for variadic operators those domain and co-domain are equals. In practice, this makes list matching and associative matching with neutral element easy to use.

If you use a hook rules, there may be an interaction that can lead to non-termination.

Therefore, no hook will be automatically added, and you are forced to declare a hook of the form AU, ACU, FL or Free.

Note: if you do not really understand what happens when you define a hook rules, the safest approach is to declare the operator as <op>:Free() {} and to encode the desired theory in the rules.

Generated API

For each Module, the Gom compiler generates an API specific of this module, possibly using the API of other modules (declared in the Imports section). This API is located in a Java package named using the ModuleName lowercased, and contains the tree implementation itself, with some additional utilities:

• an abstract class named ModuleNameAbstractType is generated. This class is the generic type for all nodes whose type is declared in this module. It declares generic functions for all tree nodes: a toATerm() method returning a aterm.ATerm • given a sort (SortName), generate a class (in a package types.SortName) for each operator. This class extends the class generated for the corresponding sort. It provides getters for the slots of the operator, and the isOperatorName() method is overridden to return true. Those classes implement the tom.library.sl.Visitable interface. It is worth noting that builtin fields are not accessible from the Visitable, and thus will not be visited by strategies. The operator class also implements a static make method, building a new instance of the operator. This make method is the only way to obtain a new instance.

public static <op> make(arg1,...,argn);

• for each list-operator, Operator for instance, the generated code contains two operator classes: one name EmptyOperator which is used to represent the empty list of arity 0, and the other named ConsOperator having two fields: one with the codomain sort, and one with the domain sort of the variadic operator, respectively named HeadOperator and

TailOperator, leading to getter functions getHeadOperatorand getTailOperator. This allows to define lists as the composition of many Cons and one Empty objects.

• for each module, one file ModuleName.tom providing a Tom mapping for the sorts and operators defined or imported by the module. completed with the methods from the Nat class and the ModAbstractType.

Example of generated API

The operators implementing the variadic operator both extend the List class, which provides list related methods, such as length, fromArray, getCollection and reverse.

The getCollection method produces a collection of objects of the codomain type corresponding to the list elements, while the reverse method returns the list with all elements in reverse order. The static fromArray method produces a list from an array of objects of the codomain type. The List class for our example then contains: Note that all the methods of the java.util.Collection that make the list mutable (for example, the removeAll method) are not implemented and thus throw an UnsupportedOperationException.

public
For the ConsList class, we obtain: );

/*

}

The congruence strategy generated for variadic operators is similar to the map strategy, and will apply its argument to all subterms of a variadic operator.

Construction strategies

Gom generated strategies' purpose is to allow to build new terms for the signature at the strategy level. Those strategies do not use the terms they are applied to, and simply create a new term. Their semantics is as follows:

(Make_a)[t] ⇒ a (Make_f(s1,s2))[t] ⇒ f(t1,t2) if (s1)[null] ⇒t1 and (s2)[null] ⇒t2, failure otherwise
We can note that as the sub-strategies for Make_f are applied to the null term, it is required that those strategies are themselves construction strategies and do not examine their argument.

These construction strategies, combined with congruence strategies can be used to implement rewrite rules as strategies. For instance, a rule f(a,b) → g(a,b) can be implemented by the strategy:

Strategy rule = `Sequence( _f(_a(),_b()), _Make_g(_Make_a(),_Make_b())

);

Fresh Gom (**)

Fresh Gom is an extension of Gom which adds capabilities very similar to that of Cαml developed by François Pottier for the Cαml programming language. In short, it extends the syntax of Gom in order to allow the specification of binding information (like : "this constructor field is in fact a variable bound in these other fields") and generates all the boring machinery to deal with fresh variables, alpha-conversion, etc. Moreover, it integrates smoothly with Tom by generating mappings which ensure that every time a constructor is matched, its concerned variables are refreshed. As an example, assume we have defined the grammar of lambda expressions using Fresh Gom. Then, when the following match instruction is run, %match( `Lambda(abs(x,u)) ) { Lambda(abs(y,v)) -> { ... } } a fresh y is generated (fresh here means an unique identifier that has never been generated before), and v is u where all instances of x have been replaced by y.

Just like Cαml, Fresh Gom allows for complex binding specifications involving several variable sorts (called atoms in the nominal logic jargon) and for nested patterns (think for instance of the meta-representation of a rewrite rule, where the variables of the left-hand side are bound in the right-hand side: you do not statically know how many -neither at which depth -variables will appear in a left-hand side). The semantics of these constructs, although intuitive enough to be grasped as is, is formally defined in this paper [2] by François Pottier.

Grammar

As mentioned, Fresh Gom extends the Gom grammar exposed above.

Raw Sorts and Constructors

Each sort concerned by Fresh Gom (i.e. connected to an atom in the sort dependency graph) is replaced by two other ones:

• a normal one, which is identical, except that every field whose sort is an atom is replaced by a String;

• a raw one, which has exactly the same definition, but whose name and constructor names have been prefixed by "Raw".

As an example, everything is as the following declarations The "raw" sorts are meant to be used at parse and pretty-printing time and do not generate any additional method than regular Gom sorts except that for conversion to "normal" sorts.

Since the pattern sort Lam is declared to bind the atoms of sort LVar, every time the constructor Lam is deconstructed, the atoms of sort LVar in the field a are refreshed. The canonical way to deconstruct such a constructor is thus to use a nested pattern as follows. Who binds what and where is specified using the 'neutral', 'inner' and 'outer' keywords. In the example above, in the abs constructor, x is in pattern position, which means that the atoms of sort LVar it contains (in that case, x itself) may be bound in the other fields of abs. If it is the case and how is specified the following way:

• 'inner' means that it is bound;

• 'outer' means that it is not bound (useful for representing let statements for instance :

in let x = u in t, x is not bound in u); • 'neutral' means it is irrelevant (here since there are no variables in types).

Compilation

The Fresh Gom mode is enable using the fresh option of Gom, as described in the tool usage documentation. It is not compatible with the termgraph option.

Examples

We present two commented examples: an interpreter for System F and a signature for a subset of ML. While the first example illustrates the use of several atom sorts, the second illustrates nested pattern sorts.

System F

Let us represent Girard's System F [3] , also known as the second-order lambda calculus.

This calculus is used as the intermediate typed representation of many functional programming languages. It has the particularity of involving two kinds of variables : terms (x,y,z...) and types (X,Y,Z...) variables, which will illustrate this particular aspect of Fresh Gom. The language is generated by the following grammar:

t,u ::= x | λx:A.t | ΛX.t | (t u) | (t A) A,B ::= X | ∀X.A | A → B
Formal presentations of the system usually go on with

• in λx:A.t, the term variable x is bound in the term t;

• in ΛX.t, the type variable X is bound in the term t;

• in ∀X.A, the type variable X is bound in the type A.

We will represent these three kind of abstraction using three pattern sorts: TermTermAbs, TypeTermAbs and TypeTypeAbs. The previous three points will be expressed using the 'inner' keyword. Note that in λx:A.t, the question of wether the term variable x is bound in the type A is irrelevant. We will express this fact using the 'neutral' keyword. The remaining of the grammar is standard Gom code.

Term-Graph Rewriting (**)

A term-graph is a term where subterms can be shared and where there may be cycles. Gom offers support to define term-graphs and term-graph rule systems. There exist several ways to define term-graphs but in our case, we propose to represent term-graphs by terms with pointers. These pointers are defined by a relative path inside the term. All the formal definitions can be found in this paper [4] .

In order to use term-graph rewriting, it is necessary to compile the Gom signatures with the termgraph option, as described in the tool usage documentation.

Term-Graph Data-Structures

When defining a Gom algebraic signature, it is possible to construct term-graphs on these signature using the option termgraph. In this case, the signature is automatically extended to manage labels. For every sort, Term for instance, two new constructors are added:

LabTerm(label:String,term:Term)

RefTerm(label:String)

With these two new constructors, users can define term-graphs as labelled terms:

Term cyclicTerm = `LabTerm("l",f(RefTerm("l")));

Term termWithSharing = `g(RefTerm("a"),LabTerm("a",a()));

From this labelled term, users can obtain the term-graph representation with paths using the expand method. This method must be called before applying a term-graph strategy.

Term-Graph Rules

Using the hook graphrules, it is possible to define a set of term-graph rules. The first parameter (MyGraphStrat) is the name of the strategy associated to the set of rules. The second parameter is the default strategy (Identity in the following example). The left-hand and right-hand sides of these rules are term-graphs. A set of rules can only be associated to a given sort. RefTerm but using a light syntax. l:t is equivalent to LabTerm(l,t) and &l corresponds to RefTerm(l).

Contrary to classical term-graph rewriting, it is possible to reuse a label from the left-hand side in the right-hand side in order to obtain side effects. This feature is inspired from Rachid Echahed's formalism [5] .

sort Term: graphrules(SideEffect,Identity) { f(l:a()) -> g(&l,l:b())

}

This set of rules is translated into a Tom %strategy that can be used in a Tom program:

Term t = (Term) `g(RefTerm("a"),LabTerm("a",a())).expand();

`TopDown(Term.MyGraphStrat()).visit(t)

Language Reference

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Basic strategy combinators

The following operators are the key-component that can be used to define more complex strategies. In this framework, the application of a strategy to a term can fail. In Java, the failure is implemented by an exception (VisitFailure) of the package library.sl.

(myFirstStrat)[f(a(),a())] ⇒ f(b(),b()) (myFirstStrat)[f(a(),b())] ⇒ failure (myFirstStrat)[b()] ⇒ b()
Sometimes, it is interesting to get the environment where the strategy is applied. The interface Strategy has a method getEnvironment() which returns the current environment of the strategy. This is particularly interesting to obtain the position (in the subject) where the strategy is currently applied. In this case, you can call

getEnvironment().getPosition().

This information is also available through the getEnvironment() method from the AbstractStrategy class. To use this method or the following strategies which depend on it, you must call the visit method on your strategy instead of visitLight. where s is a strategy reduced to one rule x → t.

Note: the static method getEnvironment().getPosition().getReplace(i,t) returns a strategy that is not type preserving.

Strategy library

In order to define recursive strategies, we introduce the µ abstractor. This allows to give a name to the current strategy, which can be referenced later. The Try strategy never fails: it tries to apply the strategy s. If it succeeds, the result is returned. Otherwise,the Identity strategy is applied, and the subject is not modified.

The Repeat strategy applies the strategy s as many times as possible, until a failure occurs.

The last unfailing result is returned.

The strategy OnceBottomUp tries to apply the strategy s once, starting from the leftmost-innermost leaves. BottomUp looks like OnceBottomUp but is not similar: s is applied to all nodes, starting from the leaves. Note that the application of s should not fail, otherwise the whole strategy also fails.

The strategy Innermost tries to apply s as many times as possible, starting from the leaves.

This construct is useful to compute normal forms.

For example, we define myFirstInnerMost = InnerMost(s) where s is defined as the elementary strategy:

Congruence strategies (generated by Gom)

As mentioned in Section Congruence strategies, Gom automatically generates congruence and construction strategies for each constructor of the signature.

Matching and visiting a strategy (*)

Strategies can be considered as algebraic terms. For instance, the BottomUp(v) strategy corresponds to the algebraic term mu(MuVar("x"),Sequence(v,All(MuVar("x")))).

Those strategy terms can then be traversed and transformed by mean of strategies. As strategies are considered as algebraic terms, it is possible to use pattern matching on the elementary strategies of the strategy language.

The following function uses pattern matching on a strategy expression, to identify a

Java

To help manipulating Java data-structures, Tom provides several mappings for the Java Similarly, a list of instructions is represented by the associative operator InstructionList.

A method contains an info part and a code part. The code part is mainly composed by local variables and a list of instructions. Each bytecode instruction is represented by an algebraic constructor: Nop, Iload, etc.

In the package tom.library.bytecode, there exist two principal classes based on the ASM library:

• the BytecodeReader class whose constructor takes the path of a Java class. Its main method is getTClass() that returns the Gom representation of the Java class.

• the BytecodeGenerator class whose main method named toBytecode(TClass c) returns a byte array that corresponds to the Bytecode of the Gom term c.

Simulation of control flow by Strategies

When considering a Bytecode program, with the sl library, we can just define traversals without considering the control flow. Our suggestion is to use strategies in order to simulate the control flow during the traversal of the list of instructions. In the Tom language, the rules and the control are completely separated so an alternative for representing control flow graphs (CFG) is to use the control to indicate what is the possible following instruction. We have seen in the previous section that to apply a strategy to children, there exist two combinators All and One.

In the mapping bytecode/cfg.tom, the two combinators AllCfg and OneCfg behave almost as All and One but the considered children are the following instructions in the Control flow graph instead of the following instruction in the list. For example, the Goto instruction has one child with respect to the control flow graph (the instruction corresponding to the label). An If_XX instruction has two children: the one which satisfies the expression, and the one that does not.

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Static functions

Since version 2.3, Tom generate static functions in Java, instead of object methods. This allows to use Tom constructs in the main() function, this improves the efficiency of the generated code, and this makes safer the use of strategies.

To be compatible with the previous version, the -noStatic flag can be used.

From Vas to Gom

In the future, Gom will replace Vas. To make the migration easier, the Gom compiler accepts the Vas syntax. However, there are some minor changes:

• in Gom the importation of builtin modules (int, String,…) should be explicit,

• when using the new ML-like syntax, the defined sorts should no longer be declared,

• factories are no longer needed by the generated code. As a consequence, Java imports and constructors are simpler,

• the methods to get and set values of subterms are named after the slot name: for a slot named slot of type SlotType, the access and modification are getslot() and setslot(SlotName value). The String getName() function is now String symbolName(), and there is no more int getArity().

• The methods boolean isOperator() now use the exact name of the operator, without capitalizing it.

• when defining a list-operator, Gom automatically generates Java access functions.

getHead, getTail, and isEmpty are replaced respectively by getHeadconc, getTailconc, and isEmptyconc for a list-operator named conc.

• objects generated by Gom do no longer implement the ATerm interface. Therefore, some functionalities have disappear. In particular, genericCollect and genericTraversal can no longer be used. The strategy language has to be used instead.

• to implement strategies on a module Module, the class ModuleBasicStrategy replaces the ModuleVisitableFwd of Vas.

Migration from 2. 1 to 2. 2 Mapping definition

Since version 2.2, the mapping definition formalism has been simplified. Therefore, we are no longer able to be fully compatible with the old syntax. Some small and simple modifications have to be performed:

• in %op, the slot-names are no longer optional. For each argument of a constructor, a name has to be given. This name can then be used within the "bracket" notation.

%op T f(T,T) has to be replaced by %op T f(arg1:T,arg2:T), where arg1 and arg2 are slot-names.

• for each slot-name, a get_slot(name,t) construct has to be specified. This defines, given an object t, how to access to the slot-name named name.

The definition of get_slot can be defined by using the previously defined construct get_subterm (the first slot corresponds to the 0-th subterm, second slot to the 1-st subterm, etc.). Thus, for the previous example, we can have:

Command line options

• --protected is a new option which makes Tom generates protected access functions. By default, access functions are now private instead of public, • --noWarning has been replaced by its dual --wall (for printing warnings).

Migration from 1. 5 to 2. 0

New backquote usage

Since version 2.0, Tom integrates an optimizer which removes unused variable assignments and performs inlining optimizations. In order to make these optimizations correct, the Tom compiler needs to know whether a Tom variable (instantiated by pattern matching) is used or not.

In previous versions of Tom, it was possible to use or re-assign a Tom variable without any particular requirement. Since version 2.0, it is recommended (and needed if you want to use the optimizer) to use the backquote mechanism to retrieve the value of a Tom variable.

The syntax of a backquote construct has been modified in the following way:

• 'Name (like 'x) is now correct. This allows access to the value of a Tom variable. This construct also allows access to the value of list-variable, but the 'Name'*' construct is to be preferred, • 'Name'*' (like 'X*) is now correct. This allows access to the value of a Tom list-variable,

• 'Name( ... ) is correct, as in previous versions. This construct builds a term in memory,

• '( ... ) is now correct and can be used to simulate the previous syntax. Since version 2.0, it is no longer possible to start a backquote construct by using something different from a Name or a '('. Thus, '1+x is no longer valid: '(1+x) or 1+'x has to be used instead, • 'xml( ... ) has to be used to create an Xml term.

Command line options

• --destdir (short version: -d) option: as in javac, this option specify where to place generated files,

• --output (short version: -o) option: as in gcc, this option specify the name of the unique generated file. This option is not compatible with --destdir, • -o is no longer the short version of --noOutput.

Predefined mapping

Since version 2.0, Tom does no longer support predefined builtin sorts, via %typeint, %typestring or %typedouble. Tom comes now with a library of predefined mappings.

Among them, int.tom, string.tom and double.tom. In order to use these mappings, the %include construct should be used (i.e. %include{ int.tom } to import the predefined int mapping). Installing Tom

Tools

Requirements

Tom is a Java application written with JDK 1.5. Tom is platform independent and runs on various systems. It has been used successfully on many platforms, including Windows XP, Windows Vista, MacOS X, Linux (Debian, Mandrake, Ubuntu, Gentoo), FreeBSD, and NetBSD.

The only requirement to run and compile Tom programs is to have a recent Java Development Kit installed (version 1.5 or newer):

• Java is available for download at java.sun.com [1] . If you do not know which package to choose, select Java SE Development Kit (JDK)

[2]

Windows (simple install)

For a painless process, run the tom-2.7_setup.exe [3] kit provided (downloads [4] ). This will automatically update the environment as needed.

Windows (manual install)

If for any reason you prefer to install Tom manually, here is the procedure to follow:

We assume that Tom is installed in C:\tom (any other directory may be chosen). The following steps are needed for setting up the user variables of your environment:

• set JAVA_HOME to where Java JDK is installed (for instance: C:\Program Files\Java\jdk1.6.0_13) • set TOM_HOME to C:\tom

• set CLASSPATH to .;%TOM_HOME%\lib\tom-runtime-full.jar

• set PATH to %Path%;%TOM_HOME%\bin;%JAVA_HOME%\bin For a detailed description of setting environment variables in Windows, please refer to Windows documentation. For Windows XP, some information can be found here

Windows (with Cygwin)

We assume that Tom is installed in c:\tom. Please issue the following for setting up Tom: export TOM_HOME=/cygdrive/c/tom export PATH=${PATH}:${TOM_HOME}/bin export CLASSPATH=${TOM_HOME}/lib/tom-runtime-full.jar:${CLASSPATH} Note: we recommend to add current directory . in your CLASSPATH.

Unix

To install Tom, choose a directory (${HOME}/tom for instance) and copy the distribution files there. This directory will be called TOM_HOME in the following.

The following sets up the environment, for Bourne shell (sh) and C shell (csh) families:

Getting some examples

Many examples have been written to test or illustrate some particular behaviors. This collection of examples is available: tom-examples-2.7.zip [6] (see also downloads [7] ).

Unzip the archive and use the tool Ant to compile the examples:

• Ant is available for download at ant.apache.org [8] .

Note: for Debian users, the ant package does not include the ant-optional java package, Debian (and Debian-based distributions like Ubuntu) users also need to install the ant-optional Debian package.

As cc and javac, tom can compile several input files. By default, the generated files are saved in the same directory as the corresponding input files. When compiling a Java file (i.e.

a Tom file where Java is the host language), Tom is smart enough to parse the package definition and generate the pure-Java file in the same package architecture. Similarly to javac, tom supports a -d option which allows the user to indicate where the files have to be generated. To be compatible with cc and classical Makefile, Tom also supports a -o option which can be used to specify the name of the generated file.

Note: Only if a manual installation was performed (without using the kit), Windows users can use the provided shell script javacForTom.bat in order to compile the Java files that are generated by Tom. Another script, javaForTom.bat can be used to execute the Java bytecode. We recommend the use of these scripts since they update the CLASSPATH according to the '*.jar' files that are in the distribution. If you used the install kit, the CLASSPATH was updated accordingly at the install time.

Command line tool tom [options] filename[.t]

The command takes only one file argument, the name of the input file to be compiled. By convention the input file name is expected to be of the form filename.t, whatever the used host language is.

Options:

-

Ant task

Tom provides an ant task for running the Tom compiler within the apache ant [1] build system.

The Tom ant task is very close in use to the javac ant task. Since this task is not part of the official ant tasks, you have first to declare this task in your buildfile, in order to use it.

This is done by the following code:

  Java --%gom // import class.module.types.* whith lower case names import algebraic.logic.types.time equality check thanks to maximal sharing Proposition p1 = `Q(nat(3)); Proposition p2 = `Q(nat(3)); System.out.println(p1 == p2);

}

  public static String prettyTerm(Term t) { %match(t) { nat(i) -> { return Integer.toString(`i); } var(x) -> { return `x; } plus(t1,t2) -> { return prettyTerm(`t1) + " searchCars(Vehicle subject){ %match(subject){ !car(x,x,_) -> { System.out.println( "-Not a car, or car with different colors:\t\t" that is not ecological and that does not\n"+ " have the same interior and exterior colors: \t\t" main(String[] args) { Vehicle veh1 = `bike(); Vehicle veh2 = `car(red(),green(),ecological()); Vehicle veh3 = `car(red(),red(),ecological()); Vehicle veh4 = `car(green(),green(),ecological()); Vehicle veh5 = `car(green(),red(),polluting($ tom Anti.t && javac Anti.java && java Anti -Not a car, or car with different colors: bike() -Not a car, or car with different colors: car(red(),green(),ecological()) -Ecological car and that has the same interior and exterior colors, but different from green: car(red(),red(),ecological()) -Not a car, or car with different colors: car(green(),red(),polluting()) -Car that is not ecological and that does not have the same interior and exterior colors: car(green(),red(),polluting()) Computing a fixpoint --%strategy, RepeatId import rmdoubles.mylist.types.*; import tom.library.sl.*; // imports the runtime strategy library public class RmDoubles { // includes description of strategy operators for tom (RepeatId here) define a 'user strategy' which should be seen as a rewrite system (composed of only one rule here) */ %strategy Remove() extends `Identity() { visit StrList { (X*,i,Y*,i,Z*) -> { return `strlist(X*,i,Y*,Z*); } } } public static void main(String[] args) throws VisitFailure {

  is a rewrite system which simplifies expressions.It is meant to be applied on any sub-expression of a bigger one, not only in head. */ %strategy EvalExpr() extends Identity() { visit Expr { plus(l1*,val(x),l2*,val(y),l3*) -> { return `plus(l1*,l2*,l3*,val(x + y)); } mult(l1*,val(x),l2*,val(y),l3*) -> { return `mult(l1*,l2*,l3*,val(x * y)); } plus(v@val(_)) -> { return `v; } mult(v@val(_)) -> { return `v; } } } public static void main(String[] args) throws VisitFailure { Expr e =

  import collect.logic.types.*; import tom.library.sl.*; import java.util.LinkedList; import java.util.HashSet; public class Collect { %include { sl.tom } /* Since strategies arguments (Collection c here) have to be seen as algebraic terms by tom, we include the tom's java Collection description */ %include { util/types/Collection.tom strategy takes a java Collection as an argument and performs some side-effect (add). */ %strategy CollectVars(Collection c) extends `Identity() { visit Term { v@var(_) -> { c.add(`v); } } } public static void main(String[] args) throws VisitFailure { Prop p = `forall("x", implies(implies(P(f(var("x"))), P(var("y"))),P(f(var("y"))))); /* We choose an HashSet as a collection and we apply the collector to the proposition p in a TopDown way */ HashSet result = new HashSet(); `TopDown(CollectVars(result)).visit(p); System.out.println("vars: " + result); } } tomuser@huggy$ tom Collect.t && javac Collect.java && java Collect vars: [var("x"), var("y")] Collecting free variables --mu operator, composed strategies import advanced.logic.types.*; import tom.library.sl.*; import java.util.LinkedList; public class Advanced { %include { sl.tom } %include { util/types/Collection.tom If the strategy encounters 'forall name, ...', then it returns the identity. -If it encounters 'name', then it adds its position to the collection c. -By default, it fails. (extends Fails) */ %strategy CollectFree(String name, Collection c) extends Fail() { visit Prop { p@forall(x,_) -> { if(`x == name) return `p; } } visit Term { v@var(x) -> { if(`x == name) c.add(getEnvironment().getPosition()); } } } private static LinkedList<Position> collectFreeOccurences(String name, Prop p) throws VisitFailure { LinkedList res = new LinkedList(); /* This strategy means: -try to apply CollectFree on the current term -if it worked then stop here -else apply yourself (mu operator) on all the subterms of the current term */ `mu(MuVar("x"), Choice(CollectFree(name,res),All(MuVar("x")))).visit(p); return res; } public static void main(String[] args) throws VisitFailure {

  define a normalizing rewrite system for the module (only one rule here) */ module sortedlist:rules() { /* everytime a term with 'sorted' as an head symbol is constructed, the following conditional rewrite rule is applied, hence ensuring an invariant on the lists */ sorted(x,y,t*) -> sorted(y,x,t*) if y <= x } } public static void main(String[] args) { Integers l1 = `sorted(7,5,3,1,9); Integers l2 = `sorted(8,4,6,2,0); Integers l3 = `sorted(l1*,10,l2*);

  hook is triggered everytime a term with 'sorted' as an head symbol is constructed */ sorted:make_insert(e,l) { %match(l) { sorted(head,tail*) -> { /* The 'realMake' function constructs the term without calling the associated hook in order to avoid infinite loops. */ if(e >= `head) { // hooks are pure tom-java so we allow any side effect System.out.println(e + " is greater than the head of " + `tail); return `realMake(head,sorted(e,tail*)main(String[] args) {

  .println("list = " + l); /* We can match linked lists like any other associative constructor. Since we declare the Sort (LinkedList) in the %match construct, we can use the implicit notation (without the constructor name) in the patterns and thus do not need to look at the mapping file. */ %match(LinkedList l) { (_*,x,_*) -> { System.out.println("iterate: " + `x); } (_*,x,_*,x,_*) -> { System.out.println("appears twice: ,x,_*), !(_*,x,_*,x,_*) -> { System.out.println("appears only once: " + `x); need to include the standard mappings for java integers and strings since we declare fields of these sorts in the following mapping */ %include { int.tom } %include { string.tom } /* This class is here for pedagogic reasons. We could have worked with the only 'Car' class */ private static class Vehicle { } /* This demo class declares two fields with the corresponding getters and setters, as well as a custom version of equals. */ private static class Car extends Vehicle { private int seats = 0; private String color = null; public Car(int seats, String color) { this.seats = seats; this.color = color; } public int getSeats() { return seats; } public String getColor() { return color; } public void setSeats(int s) { seats = s; } public void setColor(String c) { color = c; } public boolean equals(Car c) { return c.seats == seats && c.color.equals(color); } } /* We define a mapping for the Vehicle and Car classes so that it behave like the following gom signature: Vehicle = car(seats:int, color:String) */ // typeterm defines a Sort (Car here) %typeterm Vehicle { // The corresponding java type implement { HandMapping.Car } // How to check the sort is_sort(c) { c instanceof HandMapping.Car } // How to check the equality between two terms of sort Car equals(c1,c2) { c1.equals(c2) } } %op Vehicle car(seats:int, color:String) { // Is the head symbol of the tested term a car ? .println("this red car has " + `s + " seats"); } } %match (c1,c3) { car(_,c), car(_,c) -> { System.out.println("c1 and c3 have the same " + `c + " color"that we use the definition of equality here x@car(s,c), x -> { System.out.println("This is the same "+`c +" car with "+`s $ tom HandMapping.t && javac HandMapping.java && java HandMapping this red car has 6 seats c1 and c3 have the same blue color This is the same blue car with 4 seats option --termgraph, it is possible to automatically generate from a signature the extended version for term-graphs. As the Tom terms are implemented with maximal sharing, so are the term-graphs. Term-graphs can be specified using label constructors. (previous:List,element:Term,next:List) | nil() | insert(element:Term,list:List) sort List: graphrules(Insert,Identity) { insert(x1,v:doublelinkedlist(p,x2,n)) -> l:doublelinkedlist(p,x1,v:doublelinkedlist(&l,x2,n2",insert(b(),LabList("3",doublelinkedlist(RefList("1"),c(), doublelinkedlist(RefList("3"),d(),nil()))))))).expand(); System.out.println("Original subject");Viewer.display(abcd); System.out.println("Insertion with term-graph rules from Gom"a system of term-graph rules and it is automatically compiled in a basic

  part, we introduce the basic notions provided by Tom: the definition of a data-type, the construction of data (i.e. trees), and the transformation of such data using pattern-matching. Defining a data-structure One of the most simple Tom programs is the following. It defines a data-type to represent Peano integers and builds the integers 0=zero and 1=suc(zero): import main.peano.types.void main(String[] args) { Nat z = `zero(); Nat one = `suc(z); System.out.println(z); System.out.println(one); } }

  void main(String[] args) { Nat two = `plus(suc(zero()),suc(zero())); System.out.println(two); two = evaluate(two); System.out.println(two); } public static Nat evaluate(Nat n) { %match(n) { plus(x, zero()) -> { return `x; } plus(x, suc(y)) -> { return `suc(plus(x,y)

  a) Or(a, b) → Nand(Not(a), Not(b)) And(a, b) → Not(Nand(a, b)) Xor(a, b) → Or(And(a, Not(b)), And(Not(a), b))

  b1:Bool, b2:Bool) | Xor(b1:Bool, b2:Bool) module Logic:rules(can be used when a specific name for a variable is not needed.When using the module Logic:rules() { ... } constructs, the simplification rules are integrated into the data-structure. This means that the rules are applied any time it is possible to do a reduction. The user does not have any control on them, and thus cannot prevent from applying a rule. Of course, the simplification system should be terminating, otherwise, infinite reductions may occur. When compiling and executing the previous program, we obtain b = True().Separating Gom from Tom (*)Note: do not read this section if you are not interested in separating the data-type definition from the program itself.

  (a,a) Or(a,b) -> Nand(Not(a),Not(b)) And(a,b) -> Not(Nand(a,b)) Xor(a,b) -> Or(And(a,Not(b)),And(Not(a),bby compiled as follows: $ gom Logic.gom This generates several Java classes, among them a particular file called Logic.tom which explains to Tom how the data-structure is implemented. This process is hidden when using the %gom {...} construct: One of the simplest Tom program that uses the defined data-structure is the following: import logic.types.*; public class Main { %include{ logic/Logic.tom } public final static void main(String[] args) { Bool b = `Xor(True(),False()); System.out.println("b = " + b); } } Note: since classes are generated in the logic directory, the statement import logic.types.*; is needed. The name comes from the name of the module (Logic).

}

  Assume that we want to write an interpreter for this language, we need a notion of environment to store the value assigned to a variable. A simple solution is to use a Map which associate an expression (of sort Expr) to a name of variable (of sort String). Given this environment, the evaluation of an expression can be implemented as follows: public static Expr evalExpr(Map env,Expr expr) { %match(expr) { Var(n) -> { return (Expr)env.get(`n); } Plus(Cst(v1),Cst(v2)) -> { return `Cst(v1 + v2); } Mult(Cst(v1),Cst(v2)) -> { return `Cst(v1 * v2); } Mod(Cst(v1),Cst(v2)) -> { return `Cst(v1 % v2); } // congruence rules Plus(e1,e2) -> { return

  ("strange term: " + inst); } Note: the last two rules use the conditional test if from Java to implement a conditional rule.

  public final static void main(String[] args) { Map env = new HashMap();

}

  The %include { string.tom } construct imports the predefined (Java) mapping which defines the Tom String algebraic sort. Thus, the sort String can be used in the %match construct.

  *,L*,_*,L*,_*) -> { if(`L*.length() > 0) { System.out.println("L =

}

  Once this signature defined, it becomes possible to define patterns and ' expressions. For example, the function that removes identical consecutive elements can be expressed as follows: interesting since it expresses a complex operation in a concise way: given a list l, the %match construct looks for two identical consecutive elements (f(X1*,x,x,X2*)

  gt(E e1, E e2) { return e1.toString().compareTo(e2.toString()) > 0; } In this example, the order is implemented by the gt function, using the lexicographical ordering provided by Java.

  (), Z*=f(b(),a()), e2=a(), Y*=f() 4. X*=f(b()), e1=b(), Z*=f(), e2=a(), Y*=f(a) 5. X*=f(b()), e1=b(), Z*=f(a()), e2=a(), Y*=f() 6. X*=f(b(),b()), e1=a, Z*=f(), e2=a(), Y*=f()

  public final static void main(String[] args) { L l = `f(a(),b(),c(),a(),b(),c(),a()); L res1 = swapSort(l

}

  There exists three kinds of elementary strategy: Fail, which always fails, Identity, which always succeeds, and transformation rules of the form l → r.

}

  As an exercise, we want to write an optimization function that replaces an instruction of the form If(Neg(b),i1,i2) by a simpler one: If(b,i2,i1). A possible implementation is:public static Expr opti(Expr expr) { %match(expr) { If(Neg(b),i1,i2) -> { return `opti(If(b,i2,i1)

  the strategy given as argument of a TopDown should not fail. Otherwise, the TopDown will also fail. This is why the stratPrintCst is wrapped into a Try, which makes the strategy always successful.

  public static void printCst(Expr expr) { try { `TopDown(Try(stratPrintCst())).visit(expr); `TopDown(Try(Sequence(FindCst(),PrintTree()))).visit(expr); } catch (VisitFailure e) { System.out.println("strategy failed"

  optimize(Expr expr) { try { `Sequence(TopDown(Try(stratRenameVar())),PrintTree()).visit(expr); } catch (VisitFailure e) { System.out.println("strategy failed"); } } Note: to print the resulting term, the TopDown application of stratRenameVar (wrapped by a Try) is combined, using a Sequence, with the strategy PrintTree.

  program p4, as expected this results in:

  The '!' symbols can be nested, and therefore more complicated examples can be generated: either something different from f, or an f with x1 != x2 } f(x,!x) -> { // matches an f which has x1 != x2 } f(x,!g(x)) -> { // matches an f which has either x2!=g or x2=g(y) with y !

  %match(listSubject) {!List(_*,a(),_*) -> { System.out.println("The list doesn't contain 'a'"); a list that has at least one element different from a().

  %match(listSubject) { !List(_*,!a(),_*) -> { // matches a list that contains only 'a()' } !List(X*,X*) -> { // matches a non-symmetrical list } !List(_*,x,_*,x,_*) -> { // matches a list that has all the elements distinct } List(_*,x,_*,!x,_*) -> { // matches a list that has at least two elements that are distinct } } ...

  now suppose that we have the following %match construct: flag = true; } f(a(),b()) -> { flag = true; } } if (flag) { /* some action */ } } g(_) -> { System.out.println("a g(_)"); } } ...This is a very basic example where we want to check if the subject is an f with the second sub-term either g(a()) or f(a(),b()). If it is the case, we want to perform an action.Using the new syntax of the %match construct (detailed in the language reference), we could write the following equivalent code:... %match(subject) { f(x,y) && ( g(a()) << y || f(a(),b()) << y ) -> { /* some action */ } g(_) -> { System.out.println("g()"); } } ... The %match construct can be also used without any parameters. The following three constructs are all equivalent: ... %match(subject1, subject2) { p1,p2 -> { /* action 1 */ } p3,p4 -> { /* action 2 << subject2 -> { /* action 1 */ } p3 && p4 << subject2 -> { /* action 2 */ } } ... ... %match { p1 << subject1 && p2 << subject2 -> { /* action 1 */ } p3 << subject1 && p4 << subject2 -> { /* action 2 */ } } ... A big advantage of the this approach compared to the classical one is its flexibility. The right-hand side of a match constraint can be a term built on variables coming from the left-hand sides of other constraints, as we saw in the first example of this section. A more advanced example could verify for instance that a list only contains two occurrences of an object: ... %match(sList) { List(X*,a(),Y*,a(),Z*) && !List(_*,a(),_*) << List(X*,Y*,Z*) -> { System.out.println("Only two objects a()");

  ); %match(sList) { intList(_*,x,_*) && x > 5 -> { System.out.println(`x); As inside a %strategy we have in fact the body of a %match, we can of course use the constraints in the left-hand side of the rules exactly as we do in the case of %match. For instance, we may write: ... %strategy MyStrat() extends Identity() { visit E { f(x,y) && ( g(a()) << y || f(a(),b()) << y ) -> { /* some action */ } } } ... This is particulary useful even for simple conjunctions, as in a %strategy we cannot have multiple subjects like in %match.

  %match {x << a() || x << b() -> { System.out.println("here x=" + `x); Level 1 > Level 2 > Level 3 > Advanced > XML

}

  The makeAFun function has three arguments: the function name, the number of arguments and a boolean that indicates if the quotes are included in the function name or not.Given this mapping, Tom can be used as previously: the following function implements the addition of two Peano integers: public ATermAppl plus(ATermAppl t1, ATermAppl t2) { %match(t2) { zero() -> { return t1; } suc(y) -> { return `suc(plus(t1,y)); } } return null; } Advanced examples Let us suppose that we have a Java class Person with two getters (getFirstname and getLastname). In order to illustrate the signature definition formalism, we try to redefine (without using Gom) the abstract data type for the sort Person. The first thing to do consists in defining the Tom sort Person: %typeterm Person { implement { Person } } To avoid any confusion, we use the same name twice: the Tom sort Person is implemented by the Java class Person. When declaring an operator, we defined the behavior as shown in the previous example: %op Person person(firstname:String, lastname:String) { is_fsym(t) { t instanceof Person } get_slot(firstname,t) { t.getFirstname() } get_slot(lastname,t) { t.getLastname() } make(t0, t1) { new Person(t0, t1) } }

  private static ArrayList myAdd(Object e,ArrayList l) { l.add(e); return l; } private static ArrayList myEmpty(int n) { ArrayList res = new ArrayList(n); return res; } Usually, we use an associative operator to represent (in a abstract way) a list data structure. There are many ways to implement a list, but the two most well-known are the use of array based list, and the use of linked-list. The previously described mapping shows how to map an abstract list to an array based implementation.

<

  ref="#dynamic.clickstream"/> <DATA ref="#dynamic.http"/> <DATA ref="#dynamic.clientevents"/> <DATA ref="#user.home-info.postal.country"/> <DATA ref="#dynamic.cookies"> <CATEGORIES> <content/> </CATEGORIES> </DATA> <The client's policy is the following file client.xml: <RULESET appel="http://www.w3.org/2002/04/APPELv1" p3p="http://www.w3.org/2000/12/P3Pv1" crtdby="W3C" crtdon="2001-02-19T16:21:21+01:00"> ... <RULE behavior="limited1" prompt="yes"> <POLICY> <STATEMENT> <PURPOSE connective="and-exact"> <current/> </PURPOSE> <RECIPIENT connective="or"> <other-recipient/ref="#dynamic.clientevents"> </DATA> <DATA ref="#dynamic.clickstream"/> For expository reasons, we consider only a sub-problem in which we say that a client's policy is compatible with the server's policy if all ref attributes from a <DATA></DATA> node also appear on the server side. In the considered examples, the policies are compatible because <DATA-GROUP> <DATA ref="#dynamic.clientevents"> </DATA> <DATA ref="#dynamic.clickstream"/> </DATA-GROUP> is included in: <DATA-GROUP> <DATA ref="#dynamic.clickstream"/> <DATA ref="#dynamic.http"/> <DATA ref="#dynamic.clientevents"/> <DATA ref="#user.home-info.postal.country"/> <DATA ref="#dynamic.cookies"> <CATEGORIES> <content/> </CATEGORIES> </DATA> </DATA-GROUP>

}

  import tom.library.xml.*; import tom.library.adt.tnode.*; import tom.library.adt.tnode.types.*; import aterm.*; import java.util.*; public class Evaluator { %include{ adt/tnode/TNode.tom } private XmlTools xtools; public static void main (String args[]) { xtools = new XmlTools(); TNode server = (TNode)xtools.convertXMLToATerm("server.xml"); TNode client = (TNode)xtools.convertXMLToATerm("client.xml"); As explained in Part documentation:Tom (Tom language description), to each Xml document corresponds a DOM (Document Object Model) representation. In Tom, we have defined a mapping from DOM sorts to abstract algebraic sorts: TNode and TNodeList, which correspond respectively to Node and NodeList, defined by the Java DOM implementation.

}

  The first pattern means that a <DATA-GROUP></DATA-GROUP> node has to be found under a <STATEMENT></STATEMENT> node, which should be under a <POLICY></POLICY> node, which should be under a <POLICIES></POLICIES> node. Once such a pattern is found, the mechanism allows us to give a name (datagroup) to this subterm and reuse it in the action part: return datagroup;.The Xml notation implicitly extends the given patterns by adding context variables. Thus, the <DATA-GROUP></DATA-GROUP> pattern means that a subterm those head symbol is <DATA-GROUP></DATA-GROUP> is searched. But this subterm can contain attributes and children even if it is not explicitly defined by the notation. To make the definition of patterns more precise, the user can use the explicit notation and define the following pattern: <DATA-GROUP (_*)>(_*)</DATA-GROUP>. A more detailed explanation can be found in the XML Pattern part (Tom language description).

}}

  Given a <DATA-GROUP></DATA-GROUP> tree, we look for a <DATA></DATA> subtree which contains an attribute named ref.When such an attribute exists, its content (a string) is stored into the Java reftext variable. The appearsIn function is then used to check that the attribute also appears on the server side.private static boolean appearsIn(String refclient, TNode server)This piece of code is interesting because it introduces what we call "conditional rules".

  /DATA-GROUP> node. Instead of statically specifying the path (POLICIES, POLICY, STATEMENT, DATA-GROUP and RULESET, RULE, POLICY, STATEMENT, DATA-GROUP) we could have used the composed strategy TopDownCollect provided by the package tom.library.sl.*. In the following, we generalize the previous problem by considering that we can have more than one appearance of the <DATA-GROUP></DATA-GROUP> node per Xml document.We further expose the use of the strategy library. The collectDatagroup method creates a strategy TopDownCollect(collectDatagroup(set)) and then it calls the visit method on the Xml document. This strategy collects every occurence of <DATA-GROUP></DATA-GROUP> in the XML document. Using the %strategy statement, we define the basic strategy collectDatagroup parameterized by a Java set: %include{ java/util/types/Set.tom } %include{ sl.tom } %strategy collectDatagroup(set:Set) extends `Identity(, the getDataGroup method uses the Java for statement to iterate on the set and select the first collected <DATA-GROUP></DATA-GROUP> node. (<DATA-GROUP/>);}Building and sorting Xml/ DOM documentsIn this section, we consider a DOM mapping for Xml documents. This means that Xml documents are still considered as algebraic terms (built over TNode and TNodeList), but their internal representation is backed by the W3C[1] DOM library.In the following, we consider a small data-base represented by an Xml document person.xml:

  import org.w3c.dom.*; import javax.xml.parsers.*; import javax.xml.transform.*; import javax.xml.transform.dom.DOMSource; import javax.xml.transform.stream.StreamResult;

}

  In this example, it is interesting to note that an Xml node is seen as an associative operator.

}

  The pattern <Persons>(X1*,p1,X2*,p2,X3*)</Persons> looks for two elements p1 and p2 and stores the remaining contexts in X1*, X2*, and X3*. In order to give a name to contexts (and then retrieve them to build a new list), the pattern is written in explicit notation. This notation prevents Tom to add extra variables. Otherwise, the expanded form of <Persons>X1* p1 X2* p2 X3*</Persons> (written in explicit notation) would have been <Persons>(_*,X1*,_*,p1,_*,X2*,_*,p2,_*,X3*,_*)</Persons>.

  , we use the notion of anonymous Xml node (<_>...</_>) which allows to describe more generic algorithms.TutorialLevel 1 > Level 2 > Level 3 > Advanced > XML > Strategies > Runtime Library > Migration guideNotationsThe syntax of the language is given in BNF-like notation. Terminal symbols are set in typewriter font ('like this'). Non-terminal symbols are set in italic font (like that). Square brackets [...] denote optional components. Parentheses with a trailing star sign (...)* denotes zero, one or several repetitions of the enclosed components. Parentheses with a trailing plus sign (...)+ denote one or several repetitions of the enclosed components. Parentheses (...) denote grouping. (Letter | ('\' ('n' | 't' | 'b' | 'r' | 'f' | '\' | ''' | '"') ) )* '"' Letter ::= 'A' ... 'Z' | 'a' ...

A

  HelloWorld { %include { string.tom } public final static void main(String[] args) { String who = "World"; %match(who) {"World" -> { System.out.println("Hello " + who)Tom program is a list of blocks, where each block is either a Tom construct, or a sequence of characters (host language code). When compiling a Tom program, the Tom constructs are transformed into host language code, and the result is a valid host language program. For instance, in the previous example, %include and %match constructs are replaced by function definitions and Java instructions, making the resulting program a correct Java program.

  action 1: code that uses y */ } f(x,g(b())) -> { /* action 2: code that uses x */ } f(x,y) -> { /* action 3: code that uses x and y */ } } The %match construct is defined as follows: MatchConstruct ::= '%match' '(' MatchArguments ')' '{' ( PatternAction )* '}' | '%match' '{' ( ConstraintAction )* '}' MatchArguments ::= [Type] Term ( ',' [Type] Term )* |'>=' |'<' |'<=' |'==' |'!='

  are semantically equivalent. The expression p << s denotes a match constraint between the pattern p and the subject s. The advantage of this new syntax is the modularity that it offers. For instance, multiple constraints can be combined with the boolean connectors '&&' and '||', leading to a greater expressivity, sometimes closed to the one offered by regular expressions.The two syntaxes are compatible. For instance the following construct is valid: The right-hand sides of the constraints may contain variables that can be found in the left-hand side of other constraints. For instance we may write: %match(s) { f(a(),g(y)) && ( g(z) << y || f(z,_) << y ) -> { /* action 1 : code that uses y and z */ } f(x,g(b())) && f(y,a()) << someHostFunction(x) -> { /* action 2 : code that uses x and y */ } } where someHostFunction can be an arbitrary function from the host language.

  Term syntax, both Tom and host-language variables can be used and Name can be either a function symbol declared in Tom or the name of a method from the host language.Note: since version 2.4, negative patterns, called anti-patterns have been introduced. See section Anti-Pattern for a detailed description.

  is possible to insert in this string the content of a String variable, or the result of a function call (if it is a String) using the '@' as escape character: the code contained between '@' in this construct will be evaluated and the result inserted in the surrounding formatted string. Then, to add to the HelloWorld example a version string, static void main(String[] args) { System.out.println("Hello\n\tWorld @version@");

  fresh' | '--termgraph' | ... (see Gom tool for the list of available options)

  ",[],[Element("B",[Attribute("attribute","name")],[])]). When defining an XML pattern, the user has to introduce extra list-variables to precisely describe the XML pattern and capture the different contexts. Suppose that we are interested in finding a node <B></B> which is a subterm of a node <A></A> (",[_*],[_*,Element("B",[_*],[_*]),_*]). Using the XML notation, this pattern should be expressed as follows: <A(_*)>(_*,<B(_*)>(_*)</B>,_*)</A>. This notation (called explicit) is precise but error prone. This is why we have introduced the explicit notation, where all context variable can be removed (and () are replaced by []): <A[]><B[]>[]</B></A>. The last notation (called standard XML notation) allows the user to remove the [] and replace the list-separator (,) by spaces. The previous pattern can be written: <A><B></B></A>. These three different notations allow the user to choose the level of control he wants to have on the XML pattern matching algorithm.The formal description of the syntax is the following:

called

  Module, all files are generated in a directory named module and the Tom program should do the following: to combine Gom with Tom is to use the %gom construct offered by Tom.In that case, the Gom module can be directly included into the Tom file, using the %gom instruction:

  do alter the behavior of the construction functions in the term structure, it is required in a module that the rules in a 'rules' hook have as left-hand side a pattern rooted by an operator of the current module. The rules are tried in the order of their definitions, and the first matching rule is applied.

  representation of the tree; a symbolName() method returning a String representation for the function symbol of the tree root; the toString() method, which returns a string representation. public aterm.ATerm toATerm(); public String symbolName(); public int compareTo(Object o); public int compareToLPO(Object o); public void toStringBuilder(java.lang.StringBuilder buffer); • in a subpackage types, Gom generates one class for each sort defined in the module, whose name corresponds to the sort name. Each sort class extends ModuleNameAbstractType for the module, and declares a boolean method isOperatorName() for each operator in the module (false by default). It declares getters (methods named getSlotName()) for each slot used in any operator of the sort (throwing an exception by default). A method SlotName fromTerm(aterm.ATerm trm) is generated, allowing to use ATerm as an exchange format. The methods SlotName fromString(String s) and SlotName fromStream(InputStream stream) allow the use of an ATerm representation in String or stream form, to store terms in file and read them back. public boolean is<op>(); public <SlotType> get<slotName>(); public <SortName> set<slotName>(<SlotType>); public static <SortName> fromTerm(aterm.ATerm trm); public static <SortName> fromString(String s); public static <SortName> fromStream(java.io.InputStream stream) throws java.io.IOException; public int length(); public <SortName> reverse();

  | SortName ['binds' AtomName+] '=' PatternDefinition OperatorDefinition ::= ... | OperatorName'(' '<' SortName '>' '*' ')'SlotDefinition)*]')' ' | 'outer' | 'neutral'] SlotName':' SortName Description Atoms For each atom declared, Fresh Gom generates a class and a Tom sort of the same name. For example, a Gom module containing the line atom LambdaVar will generate a class LambdaVar along with the declaration of a tom sort %typeterm LambdaVar { implements LambdaVar } at the usual places. Everything is as an usual Gom sort for which no constructors had been declared. The implementation of these atoms remains opaque to the user. The unique way to create an atom of name AtomName is to use the following generated static method which creates a fresh identifier. public abstract class AtomName { public static AtomName freshAtomName() { ... } }

  sort Term: graphrules(MyGraphStrat,Identity) { g(l:a(),&l) -> f(b()) f(g(g(a(),&l),l:x)) -> g(ll:b(),&ll) if b()<<x } In the rules, sharings and cycles are not represented by the constructor LabTerm and

  Sequence(All(x),Try(Sequence(s,x)))

  becomes quite easy to define various strategies on top of this elementary strategy:Term subject = `f(g(g(a,b),g(a,a)BottomUp(rule),Innermost(rule)).visitLight(subject)); } catch (VisitFailure e) { System.out.println("reduction failed on: " + subject); }

}

  Strategy expressions being visitable terms, we can also use the '%strategy' construction to define strategy transformations, for example, removing unnecessary Identity() strategies.

  public static byte[] transform(String file){ BytecodeReader br = new BytecodeReader(file); TClass c = br.getTClass(); TClass cc = transform(c); BytecodeGenerator bg = new BytecodeGenerator(); return bg.toBytecode(cc); }

  Installation > Compiling from sources > Using Tom > Using Gom > Configuring your environment > Tom Server from sources > Using Tom > Using Gom > Configuring your environment > Tom Server

  (sh) export TOM_HOME=${HOME}/tom export PATH=${PATH}:${TOM_HOME}/bin export CLASSPATH=${TOM_HOME}/lib/tom-runtime-full.jar:${CLASSPATH} (csh) setenv TOM_HOME ${HOME}/tom set path=( $path ${TOM_HOME}/bin ) setenv CLASSPATH ${TOM_HOME}/lib/tom-runtime-full.jar:${CLASSPATH} Note: we recommend to add current directory . in your CLASSPATH.

  -config | -X <file> Define an alternate XML configuration file Allow to define the plugins instantiated by the Tom platform --cCode | -cGenerate C code (default is Java)The output file has the extension .tom.c --camlCode Generate Caml code (default is Java)--camlSemanticsVerify with caml semantics for match) Specify where to place generated files.By default, Tom generates files close to the input file. However (like javac), this option allows to specify a directory where generated files have to be put.When compiling aJava file, Tom is smart enough to parse the package definition and generate the pure-Java file in the same package architecture. description of each available options --import <path> | -I Path to included files Even if inclusion can be performed using relative path, this option specifies list of path where Tom look for when an inclusion has to be done by %include construct --inline Inline mapping --inlineplus Force inlining, even if no $ is used --intermediate | -i Generate intermediate files The compiler manipulates Abstract Syntax Trees. This option dumps the AST after each phase (parsing, checking, expansion, compilation) This option is useful to analyze the compilation process --jCode | -j Generate Java code (by default) --lazyType | -l Use universal type This option makes Tom using a less restrictive backend. In Java, the universal sort Object is used more often. This reduces static typing but allows to manipulate inherited data-structures --noDeclaration | -D Do not generate code for declarations Avoid multiple declaration of symbols when structures are inherited or when multiple inclusion of common data structures are performed --noOutput Do not generate code No output file is generated. It allows to see warnings and errors without generating the result --noReduce Do not simplify extracted constraints (depends on -verify)

  <taskdef name="tom" classname="tom.engine.tools.ant.TomTask"> <classpath refid="tom.classpath"/> </taskdef> where tom.classpath is the path reference containing all the jar's in Tom's distribution predefined in the file ${TOM_HOME}/lib/tom-common.xml.This task is used to produce Java code from Tom programs. A typical use of the Tom ant task is:<tom config="${tom.configfile}" srcdir="${src.dir}"destdir="${gen.dir}" options="-I ${mapping.dir}"> <include name="**/*.t"/></tom>Here, we want to compile all Tom source files in {src.dir}, having the generated code in {gen.dir}, and we configure the compiler to use the {tom.configfile} config file, and pass the options we want like, for example {-I} to indicate the mapping needed for compilation, just as we do for Tom in command line.Another use of this task is:<tom config="${tom.configfile}" srcdir="${src.dir}" outputfile="${gen.dir}/Example.java" options="-I ${mapping.dir}"> <include name="**/Example.t"/></tom>Here we compile only one Tom file, and specify directly the output file name we want to use.The main usecases for the Tom ant task can be found in Tom's own buildfile and the distributed examples.The Tom ant task takes the following arguments: Attribute Description Required For example, if you have a directory called tom_example with Tom source files and Gom source files which generate the Tom mapping required by tom_example, you can create the following Ant script to compile all Gom, Tom and Java code.: <?xml version="1.0" encoding="ISO-8859-1"?> <project name="Example Ant for TOM" basedir="." default="compile"> <description> A simple example of build script using Ant offering compilation of TOM programs. </description> <!--Initializing Tom and Gom --> <property environment="env"/> <property name="tom.home" value="${env.TOM_HOME}"/> <import file="${tom.home}/lib/tom-common.xml"/> <!--Defining folders --> <property name="my_example" value="tom_example"/> <property name="src.dir" value="."/> <property name="gen.dir" value="gen"/> <property name="build.dir" value="build"/> <property name="mapping.dir" value="${gen.dir}/${my_example}/${my_example}"/> <!--Declaring Tom task --> <taskdef name="tom" classname="tom.engine.tools.ant.TomTask"> <classpath refid="tom.classpath"/> </taskdef> <!--Declaring Gom task --> <taskdef name="gom" classname="tom.gom.tools.ant.GomTask" classpathref="tom.classpath"/> <target name="init" depends="tom.init" description="To realize initialization"> <mkdir dir="${gen.dir}"/> <mkdir dir="${build.dir}"/> </target> <target name="compile" depends="init" description="To compile all programs"> <!--Compiling Gom programs --> <gom config="${gomconfigfile}" srcdir="${src.dir}" package="${my_example}" destdir="${gen.dir}"> <include name="**/*.gom"/> </gom> <!--Compiling Tom programs --> <tom config="${tomconfigfile}" srcdir="${src.dir}" destdir="${gen.dir}" options="-I ${mapping.dir}"> <include name="**/*.t"/> </tom> <!--Compiling Java programs --> <javac srcdir="${gen.dir}" destdir="${build.dir}"> <classpath path="${build.dir}"/> <include name="**/*.java"/> clean" description="To remove generated code"> <delete dir="${gen.dir}"/> <delete dir="${build.dir}"/> from sources > Using Tom > Using Gom > Configuring your environment > Tom Server Tom Documentation Guided Tour :: Tutorial :: Language Reference :: Tools

Hello World" revisited: introduction to list- matching

	matchblock: { In this example, we have introduced two new variables (before* and after*), called
	%match(who) { "variable-star", which are instantiated by a list of characters, instead of a single character
	"World" -> { System.out.println("Hello " + who); (if the '*' was not there).
	break matchblock; Suppose now that we look for a word whose last letter is a 'o':
	} -> { System.out.println("Don't panic"); } concString(before*,'o') -> { ... } _ %match(t) { } } }
	} Using this mechanism, it also becomes possible to look for a word which contains an 'e'
	} somewhere and an 'o' in last position:
	%match(t) { concString(before*,'e',_*,'o') -> { ... } } "One particularity of Tom is to simplify the manipulation of lists. Note that a single pattern could provide several outcomes:
	It is natural to consider a string as a list of characters. Characters can be concatenated to %match(t) {
	from a string, and string can also be concatenated. In Tom, we have to give a name to this concString(before*,'l',after*) -> {
	concatenation operator. Let us call it concString. System.out.println("we have found " + `before* +
	Thus,	the	string	"Hello"	is	equivalent	to	the	list	of	characters
	concString('H','e','l','l','o').
	Note: concString does not have a fixed arity. concString() corresponds to the empty list of characters, i.e. the
	string "".
	Given a string, to check if the string contains the character 'e', we can use the following
	matching construct:
	public class HelloWorld {
	%include { string.tom }
	public final static void main(String[] args) {
	%match("Hello") {
	concString(_*,'e',_*) -> { System.out.println("we have found a
	'e'"); }
	}
	}
	}
	In this example, '_*' corresponds to an anonymous variable which can be instantiated by
	any list of characters (possibly reduced to the empty list).
	In order to capture the context (i.e. what is before and after the 'e'), it is possible to use
	named variables:
	To use a break statement in a %match construct, we recommend to use the notion of %match(t) {
	labeled block: concString(before*,'e',after*) -> {
	System.out.println("we have found a 'e'" + public class HelloWorld { " after " + `before* + %include { string.tom } " but before " + `after*); public final static void main(String[] args) { } String who = "World"; }

  This example is inspired from a practical study. It involves a simple modeling of the Platform for Privacy Preferences Project (P3P), developed by the World Wide Web Consortium, which is emerging as an industry standard providing a simple, automated way for users to gain more control over the use of personal information on Web sites they visit.Given a client and a server, the problem consists in verifying that the client's policy is

	Documentation:XML
	Doc : Tutorial	Level 1 > Level 2 > Level 3 > Advanced > XML
	Even if this section mostly deals with Xml features, every explained technique can be used
	with other data-structures as well.
	Manipulating Xml documents
		aterm.ATermList }
	make_empty() { aterm.pure.SingletonFactory.getInstance().makeList() }
	make_insert(e,l) { l.insert(e) }
	get_head(l)	{ (aterm.ATermAppl)l.getFirst() }
	get_tail(l)	{ l.getNext() }
	is_empty(l)	{ l.isEmpty() }
	}
		Tutorial
		Level 1 > Level 2 > Level 3 > Advanced > XML
		Tom Documentation
		Guided Tour :: Tutorial :: Language Reference :: Tools

compliant with the server's policy. Both policies preferences are expressed in APPEL (A P3P Preference Exchange Language) and written in Xml. The server's policy is the following file server.xml: <POLICIES xmlns="http://www.w3.org/2002/01/P3Pv1"> <POLICY name="mypolicy" discuri="http://www.ibm.com/privacy" opturi="http://www.ibm.com/privacy" xml:lang="en">

  variables, can also be use to build a new term. In order to build an Xml document, the xml(...) function has to be used. The number of parameters depends on the Xml mapping which is used. In our case, when manipulating DOM objects, a new subtree is built is the context of a main document. This extra-parameter is given in the first argument of the xml function. Thus, 'xml(dom,<Persons>...<Persons>) builds a new <Person></Person> node, as a child of the dom document. When using the TNode.tom mapping, a library based on Gom is used. In this case, it is no longer necessary (and even not correct) to use this extra argument.

  Coming back to our example, checking if an object 't' is rooted by the symbol person can be done by checking that 't' is an instance of the class Person. Building a person can be done via the Java function new Person(...). Accessing to the slots name and age could be implemented by an access to the variables of the class Person. In practice, the following

	operator definition should work fine:
	%op TomPerson person(name:String, age:int) {
	is_fsym(t) { $t instanceof Person }
	make(t1,t2) { new Person($t1,$t2) }
	get_slot(name,t) { $t.name } // assuming that 'name' is public
	get_slot(age,t) { $t.age } // assuming that 'age' is public
	}

  We show elements of the generated API for a very simple example, featuring variadic operator. It defines natural numbers as Zero() and Suc(n), and lists of natural numbers.Using the command gom Mod.gom, the list of generated files is:The mod/types/Nat.java class provides an abstract class for all operators in the Nat sort, implementing the ModAbstractType and contains the following methods. First, the methods for checking the root operator, returning false by default:Then getter methods, throwing an UnsupportedOperationException by default, as the slot may not be present in all operators. This is convenient since at the user level, we usually manipulate objects of sort Nat, without casting them to more specific types.The fromTerm static method allows Gom data structure to be interoperable with ATerm public static mod.types.Nat fromTerm(aterm.ATerm trm)The operator implementations redefine all or some getters for the operator to return its subterms. It also provides a static make method to build a new tree rooted by this operator, and implements the tom.library.sl.Visitable interface. For instance, in the case of the

	public mod.types.Nat getpred()
	public mod.types.Nat getlhs()
	public mod.types.Nat getHeadList()
	public mod.types.Nat getrhs()
	public mod.types.Nat getTailList()
	Plus operator, the interface is:
	module Mod public static Plus make(mod.types.Nat lhs, mod.types.Nat rhs) abstract syntax public int getChildCount() Nat = Zero() public tom.library.sl.Visitable getChildAt(int index) | Suc(pred:Nat) public tom.library.sl.Visitable setChildAt(int index, | Plus(lhs:Nat,rhs:Nat) | List(Nat*) tom.library.sl.Visitable v)
	mod/Mod.tom	(the Tom mapping)
	mod/ModAbstractType.java	(abstract class for the "Mod" module)
	mod/types/Nat.java	(abstract class for the "Nat" sort)
	mod/types/nat/List.java	\
	mod/types/nat/ConsList.java	\
	mod/types/nat/EmptyList.java / Implementation for the operator "List"
	mod/types/nat/Plus.java	(Implementation for "Plus")
	mod/types/nat/Suc.java	(Implementation for "Suc")
	mod/types/nat/Zero.java	(Implementation for "Zero")
	The ModAbstractType class declares generic methods shared by all operators in the Mod
	module:
	public aterm.ATerm toATerm()
	public String symbolName()
	public String toString()
	public boolean isConsList()
	public boolean isEmptyList()
	public boolean isPlus()
	public boolean isSuc()
	public boolean isZero()

  the constructor */ public static ConsList make(mod.types.Nat _HeadList, mod.types.Nat

	(_f(s1,s2))[t]	⇒	f(t1',t2') if t = f(t1,t2), with (s1)[t1] ⇒t1' and (s2)[t2] ⇒t2',
			failure otherwise
	Thus, congruence strategies allows to discriminate terms based on how they are built, and
	to develop strategies adopting different behaviors depending on the shape of the term they
	are applied to.
	Congruence strategies are commonly used to implement a specific behavior depending on
	context (thus, it behaves like a complement to pattern matching). For instance, to print
	all first children of an operator f, it is possible to use a generic Print() strategy under a
	congruence operator.
	Strategy specPrint = `TopDown(_f(Print(),Identity()));
	Also, congruence strategies are used to implement map like strategies on tree structures.
	Consider a signature with List = Cons(e:Element,t:List) | Empty(), then we can
	define a map strategy as:
	Strategy map(Strategy arg) {
	return `mu(MuVar("x"),
	Choice(_Empty(),_Cons(arg,MuVar("x")))

  That is the difference between visitLight and visit. Only the visit method maintain an environment.

	s.visit(subject));
	} catch(VisitFailure e) {
	System.out.prinltn("Failure at position" +
	s.getEnvironment().getPosition());
	}
	The library gives several basic strategies using the position:
	(Omega(i,s))[f(t1,...,tn)]	⇒	f(t1,...,ti',...,tn) if (s)[ti] ⇒ti'
			failure if (s)[ti] fails
	(getEnvironment().getPosition().getReplace(i,t))[f(t1,...,tn)]	⇒	f(t1,...,t,...,tn)
	(getEnvironment().getPosition().getSubterm(i,t))[f(t1,...,tn)]	⇒	ti
	Note: the static method getEnvironment().getPosition().getReplace(i,t) corresponds to the strategy Omega(i,s)
	Strategy s;
	try {
	s = `OnceBottomUp(rule);

  The real signature (adt/bytecode/Bytecode.tom) contains more than 250 different constructors. The given signature shows that a class is represented by a constructor Class, which contains information such as name, packages, and imports. It also contains a list of fields and a list of methods. The latter is encoded using an associative operator MethodList.

	| Invokevirtual(owner:String, name:String,
	methodDesc:TMethodDescriptor)
	Runtime Library. The naming convention follows Java's one: ...
	java
	├── boolean.tom
	├── char.tom
	├── double.tom
	├── float.tom
	├── int.tom
	├── long.tom
	├── string.tom
	└── util
	├── ArrayList.tom
	├── HashMap.tom
	├── HashSet.tom
	├── LinkedList.tom
	├── MapEntry.tom
	├── Object.tom
	├── TreeMap.tom
	├── TreeSet.tom
	└── types
	├── AbstractCollection.tom
	├── AbstractList.tom
	├── AbstractSequentialList.tom
	├── AbstractSet.tom
	├── ArrayList.tom
	├── Collection.tom
	├── HashMap.tom
	├── HashSet.tom
	├── LinkedHashSet.tom
	├── LinkedList.tom
	├── List.tom
	├── Map.tom
	├── Object.tom
	├── Set.tom
	├── Stack.tom
	├── TreeMap.tom
	├── TreeSet.tom
	├── Vector.tom
	└── WeakHashMap.tom
	The directory types contains only %typeterm declarations.

Guided Tour :: Tutorial :: Language Reference :: Tools

Documentation:Basic Usage Source: http://tom.loria.fr/wiki/index.php5?oldid=1239 Contributors: Jcb, Pem, Polux Documentation:Data Structure Invariants Source: http://tom.loria.fr/wiki/index.php5?oldid=1240 Contributors: Jcb, Pem, Polux Documentation:Seeing Java Objects as Terms Source: http://tom.loria.fr/wiki/index.php5?oldid=1241 Contributors: Jcb, Pem, Polux Documentation:Term-Graph Rewriting Source: http://tom.loria.fr/wiki/index.php5?oldid=1242 Contributors: Emilie, Jcb, Pem, Polux Documentation:Language Basics -Level 1 Source: http://tom.loria.fr/wiki/index.php5?oldid=1243 Contributors: Jcb, Pem, Polux, 4 anonymous edits Documentation:Language Basics -Level 2 Source: http://tom.loria.fr/wiki/index.php5?oldid=1244 Contributors: Cirstea, Jcb, Pem, Polux, Tonio Documentation:Language Basics -Level 3 Source: http://tom.loria.fr/wiki/index.php5?oldid=1245 Contributors: Jcb, Pem, Polux, Tavaresc, Tonio Documentation:Advanced features Source: http://tom.loria.fr/wiki/index.php5?oldid=1246 Contributors: Jcb, Pem Documentation:XML Source: http://tom.loria.fr/wiki/index.php5?oldid=1247 Contributors: Emilie, Jcb, Pem, Polux, Tonio Documentation:Tom Source: http://tom.loria.fr/wiki/index.php5?oldid=1248 Contributors: Jcb, Pem, Polux, Tonio Documentation:Gom Source: http://tom.loria.fr/wiki/index.php5?oldid=1283 Contributors: Emilie, Jcb, Pem, Polux, Tavaresc, Tonio Documentation:Strategies Source: http://tom.loria.fr/wiki/index.php5?oldid=1250 Contributors: Jcb, Pem, Polux, Tavaresc, Tonio, 16 anonymous edits Documentation:Runtime Library Source: http://tom.loria.fr/wiki/index.php5?oldid=1317 Contributors: Jcb, Pem, Polux, Tonio, 1 anonymous edits Documentation:Migration Guide Source: http://tom.loria.fr/wiki/index.php5?oldid=1316 Contributors: Jcb, Pem, Polux, Tonio Documentation:Installation Source: http://tom.loria.fr/wiki/index.php5?oldid=1349 Contributors: Emilie, Jcb, Pem, Polux, Tavaresc, Tonio Documentation:Compiling trunk Source: http://tom.loria.fr/wiki/index.php5?oldid=1343 Contributors: Pem Documentation:Using Tom Source: http://tom.loria.fr/wiki/index.php5?oldid=1254 Contributors: Jcb, Pem, Polux, Tonio Documentation:Using Gom Source: http://tom.loria.fr/wiki/index.php5?oldid=1255 Contributors: Emilie, Jcb, Pem, Polux, Tonio Documentation:Configuring your environment Source: http://tom.loria.fr/wiki/index.php5?oldid=1256 Contributors: Jcb, Pem, Polux Documentation:Tom Server Source: http://tom.loria.fr/wiki/index.php5?oldid=1258 Contributors: Jcb, Polux

Using Eclipse

• Window->Open Perspective->Other->Java (default)

• Window->Show View->Other->Ant

expand jtom and move the build.xml file to the Ant view • in the Ant view, expand Ant for TOM and click on the stable target • click on the src.dist target Tools Installation > Compiling from sources > Using Tom > Using Gom > Configuring your environment > Tom Server Tom Documentation Guided Tour :: Tutorial :: Language Reference :: Tools

Content

The grammar for the mapping constructs is the following:

Operator ::= '%op' Type Name consists in the "inner" default allocation function. This function takes the same number of arguments as the hook. In any case, if the hooks code does not perform a return itself, this realMake function is called at the end of the hook execution, with the corresponding hooks arguments Using the expression example introduced above, we can add hooks to implement the computation of Add and Mul when both arguments are known integers (i.e. when they are Using this definition, it is impossible to have an expression containing unevaluated expressions where a value can be calculated. Thus, a procedure doing constant propagations for Id whose value is known could simply replace the Id by the corresponding Nat, and rely on this mechanism to evaluate the expression. Note that the arguments of the make hook are themselves elements built on this signature, and thus the hooks have been applied for them. In the case of hooks encoding a rewrite system, this corresponds to using an innermost strategy.

Hooks to alter the generated API

There exist four other hooks 'import', 'interface', 'block' and 'mapping' that offer possibilities to enrich the generated API. Contrary to 'make' and 'make_insert', these hooks have no parameters. Moreover, they can be associated not only to an operator but also to a module or a sort. There are few constraints on the form of the code in these hooks:

• for 'import', the code is a well-formed block of Java imports.

• for 'interface', the code is a well-formed list of Java interfaces.

• for 'block', the code is a well-formed Java block which can contain Tom code.

• for 'mapping', the code is a well-formed Tom block composed only of mappings.

The code given in the hook is just added at the correct position in the corresponding Java class:

• for a module ModuleName, in the abstract class named ModuleNameAbstractType (for now, you can only use this hook with the current module), • for a sort SortName, in the abstract class named SortName in the package types,

• for an operator OperatorName of sort SortName, in the class named SortName in the package types/SortName.

In the case of 'mapping' hooks, the corresponding code is added to the mapping generated for the signature.

Gom Antlr Adaptor

Combining Tom, Gom and Antlr is easy. The tool GomAntlrAdaptor takes a Gom signature as input and generates an adaptor to convert an AST built by Antlr into a Gom tree.

Strategies support (*)

The data structures generated by Gom do provide support for the strategy language of Tom. We assume in this section the reader is familiar with the support of Tom as described in the Strategies chapter, and illustrated in the tutorial.

Basic strategy support

The data structure generated by the Gom compiler provides support for the sl library implementing strategies for Tom. It is thus possible without any further manipulation to use the strategy language with Gom data structures. This strategy support is extended by the Gom generator by providing congruence and construction elementary strategies for all operators of the data structure. Those strategies are made available through a Tom mapping _<module>.tom generated during Gom compilation.

Congruence strategies

The congruence strategies are generated for each operator in the Gom module. For a module containing a sort Term = a() | f(lt:Term,rt:Term) congruence strategies are generated for both a and f operators, respectively called _a and _f. The semantics of those elementary strategies is as follows:

Informal Semantics

As in Cαml, the sorts defined in a Fresh Gom module are of two distinct kinds:

• the sorts the definition of which is preceded by 'binds' id1 id2 .. are called pattern sorts; • the other ones are called expression sorts.

When pattern sorts are mentioned in an expression sort constructor, they must be placed inside brackets '<' '>'. This indicates a refresh point, i.e. a field that will be refreshed whenever the enclosing constructor is deconstructed (using match). For example, consider this excerpt of a module defining a simply typed lambda-calculus: -> { return `x; } RawLLam(Rawabs1(x,T,t)) -> { return %[(fn @`x@:@`pretty(T)@ -> @`pretty(t)@)]%; } RawLApp(t,u) -> { return %[(@`pretty(t)@ @`pretty(u)@)]%; } RawTLam(Rawabs2(T,t)) -> { return %[(FN @`T@ -> @`pretty(t)@)]%; } RawTApp(t,T) -> { return %[(@`pretty(t)@ @`pretty(T)@)]%; } } throw new RuntimeException("non-exhaustive patterns"); } public static String pretty(RawType s) { %match(s) { RawTVar(X) -> { return `X; } RawForall(Rawabs3(X,T)) -> { return %[(forall @`X@, @`pretty(T)@)]%; } RawArrow(A,B) -> { return %[(@`pretty(A)@ -> @`pretty(B)@)]%; } The key point is the reduction system HeadBeta. Thanks to the mapping generated by Fresh Gom, every time an abstraction is matched, the variable are refreshed so that we avoid their potential capture. This time, we have to convert the raw term into a "normal" one to benefit of this feature.

Mini ML

The full example can be found in the Tom distribution. We focus here on how to encode (case .. of ..) expressions with the help of Fresh Gom. The key definition is that of Clause, which declares that all the atoms of sort LVar present in the pattern p are bound in the term t. Therefore, when deconstructing a Clause using the match construct of Tom, all the variables in the left-hand side of the fetched clauses are refreshed in their corresponding right-hand side.

Documentation:Strategies

Doc : Language Reference Tom > Gom > Strategies > Runtime Library > Migration guide Note: strategies are only supported in Java.

To exercise some control over the application of the rules, rewriting based languages provide abstract ways by using reflexivity and the meta-level for Maude, or the notion of rewriting strategies as in Tom. Strategies such as bottom-up, top-down or leftmost-innermost are higher-order features that describe how rewrite rules should be applied (At each step, the strategy chooses which rule is applied and in which position inside the term).

In Tom, we have developed a flexible and expressive strategy language inspired by ELAN, Stratego, and JJTraveler where high-level strategies are defined by combining low-level primitives. For example, the top-down strategy is recursively defined by Sequence(s,All(TopDown(s))). Users can define elementary strategies (corresponding to a set of rewriting rules) and control them using various combinators proposed in the sl library. This rich strategy language allows to easily define various kinds of term traversals.

In this chapter, first, we briefly present the sl library functioning. After that, we describe in detail every elementary strategy and strategy combinator. Then, we explain how the sl library can be used in combination with Gom structures.

Overview

The package tom.library.sl is mainly composed by an interface Strategy and a class for each strategy combinator.

Strategy interface

Every strategy (elementary strategy or combinator) implements the Strategy interface. To apply a strategy on a term (generally called the subject), this interface offers two methods:

• Visitable visitLight(Visitable any) visits the subject any in a light way (without environment) • Visitable visit(Visitable any) visits the subject any and manages the environment A strategy can visit any Visitable object. Any term constructed using a Tom mapping or a Gom signature is Visitable. The first method visitLight is the most efficient because it does not manage any environment. Most of time, it is sufficient. The second method depends on an environment. The visit(Visitable) method behaves like visitLight but updates at each step an environment.

When applied on a term, a strategy returns a Visitable corresponding to the result. In case of failures, these two methods throw a VisitFailure exception.

Environment

An environment is composed of the current position and the current subterm where the strategy is applied. This object corresponds to the class Environment of the package tom.library.sl and can be associated to a strategy using setEnvironment(Environment) and accessed using getEnvironment(). A position in a term is a sequence of integers that represents the path from the root of the term to the current subterm where the strategy is applied.

The method getPosition() in the Environment class returns a Position object that represents the current position. The method getSubject() allows users to get the current subterm where the strategy is applied.

To retrieve all this information from a strategy, the visit method is necessary.

Elementary strategies

Elementary strategies of sl

An elementary strategy corresponds to a minimal transformation. It could be Identity (does nothing), Fail (always fails), or a set of rewrite rules (performs an elementary rewrite step only at the root position). In our system, strategies are type-preserving and have a default behavior (introduced by the keyword extends)

The first two elementary strategies are the identity and the failure. There are defined by two corresponding classes in sl library: Identity and Fail. These two strategies have no effect on the term. The identity strategy returns the term unchanged. The failure strategy throws a VisitFailure exception.

Elementary strategies defined by users

Users can define elementary strategies by using the %strategy construction. This corresponds to a list of MatchStatement (one associated to each sort) and can be schematically seen as a set of rewriting rules.

Here is the %strategy grammar:

This strategy has a name, followed by mandatory parenthesis. Inside these parenthesis, we have optional parameters.

The 'extends' keyword defines the behavior of the default strategy that will be applied. In most cases, two default behaviors are used:

• the failure: Fail()

• the identity: Identity()

Note that this default behavior is executed if no rule can be applied or if there is no Java return statement executed in the applied rules.

The body of the strategy is a list of visited sorts. Each StrategyVisit contains a list of VisitAction that will be applied to the corresponding sort. A VisitAction is either a

PatternAction or simply a Term (equivalent to the VisitAction { return Term; }). In other words, a StrategyVisit is translated into a MatchStatement.

For instance, here is an elementary strategy RewriteSystem that can be instantiated as The application of this strategy to different subject terms gives:

We can notice that Innermost strategy never fails. If we try myFirstBottomUp = BottomUp(s) with the same subjects, we obtain always failure because if s fails on a node, the whole strategy fails.

Strategies with identity considered as failure (*)

In order to get more efficient strategies (in particular when performing leftmost-innermost normalization), we consider variants where the notion of failure corresponds to the identity.

This means that when a term cannot can be transformed by a strategy (into a different term), this is considered as a failure.

We can define a strategy trying to apply a simple rewrite system to the root of a term, The simplest way to use strategies is to apply them on data-structures generated by Gom, as this data structure implementation provides the interfaces and classes needed to use '%strategy'. In particular, all the data structure classes implement the tom.library.sl.Visitable interface used as argument of visit methods in the tom.library.sl.Strategy interface. However, it is also possible to use '%strategy' with any term implementation.

We detail here on a simple example of hand written data structure and how to use

Simple implementation of the data structure

We first present a very straightforward implementation of this data structure. It will serve as a basis and will be extended to provide support for strategies.

We first define abstract classes for the two sorts of this definition, Term and Slot, and classes for those operators extending those sort classes. In the implementation of these methods, the introspector behaves like a proxy to render any object visitable. When activating the Tom option -gi, the compiler generates in each

Tom class an inner class named LocalIntrospector that implements the tom.library.sl.Introspector interface. This class uses informations from the mappings to know how visiting the corresponding classes.

For example, we can define the following '%strategy' statement:

Java API

The documentation of the API is available here

Predefined mappings

Builtin sorts

The system comes with several predefined signature-mappings for C, Java and Caml.

Among them, let us mention:

• boolean.tom (true or false)

• char.tom (written 'a', 'b', etc.)

• double.tom (using Java grammar for double)

• float.tom (using Java grammar for float)

• int.tom (written 1, 2, 3, etc.)

• long.tom (written 1l or 1L, etc.)

• string.tom (written "a", "ab", etc.)

These mappings define, for each builtin sort of the host language, an algebraic sort that can be used in a %match or a signature definition construct. Thus, builtin values, such as f(5), g('a') or h("foo"), can be used in patterns.

The string.tom mapping is interesting because it provides an associative operator (concString) which allows the programmer to consider a string as a list of characters.

Thus, the string "foo" can be seen as the algebraic object concString('f','o','o'). By using this mapping, it becomes possible to perform pattern matching against the content of a string. The pattern concString('f',X*) will match any string which begins with the character 'f'. By using the unnamed-symbol capability, this pattern can be written:

('f',X*) instead of concString('f',X*).

To match any string which begins with the substring "fo", the corresponding pattern should be ('f','o',X*). To simplify the definitions of such patterns, Tom supports an exception which allows the programmer to write ('fo',X*) instead. Internally, the ill-formed character 'fo' is expanded into the list ('f','o').

In addition to these mappings, several other predefined mappings come with the system:

• aterm.tom and atermlist.tom provide a mapping to the C and Java version of the ATerm Library • caml/list.tom provides a mapping to the builtin notion of List in Caml

• java/dom.tom provides a mapping to the java} version of the DOM Library

Strategies

To support strategies, Tom provides a runtime library, called SL and implemented in strategy.jar. This library implements the elementary strategy combinators (Identity, Fail, All, One, Choice, Sequence, etc.) as well as basic support for the computation of positions described in section Basic Strategy Combinators.

In addition, some predefined mapping are also available to allow the description of strategies:

• sl.tom: maps the basic strategies classes, and provides a mu operator to express the recursion as well a MuVar(v:String) operator to allow the definition of complex strategies as described in Section Strategy Library.

Term viewer

The class tom.library.utils.Viewer contains a set of methods to visualize visitable Note that these methods can also be used on strategies as they are also visitable.

XML

To support the transformation of Xml documents, Tom provides a specific syntax for defining patterns, as well as several predefined mappings:

• dom.tom: maps Xml notation to a Java implementation of the DOM library • dom_1.5.tom: maps Xml notation to a Java (version 1.5) implementation of the DOM library • TNode.tom: maps Xml notation to an ATerm based representation, generated by Gom See Section XML pattern for a detailed description of the Xml facilities offered by Tom.

Bytecode transformation (*)

To manipulate Java classes, Tom provides a library which supplies a Gom term usable by Tom out of a Java class. The library enables to define transformations of this term by strategic rewriting as well as functionalities to generate a new Java class from the modified term.

This approach is similar to BCEL library [1] in the sense that we construct a complete representation of the class. But thanks to Gom, we obtain a very efficient structure with maximal sharing. Moreover, thanks to associative matching, we can easily express patterns on the bytecode and in this way, ease the definition of transformations.

The library generates a Gom term using the ASM library [2] . This term is a memory-efficient representation of the Java class, which can then be traversed and transformed using Tom.

After translating the Java class into a Gom term, we use Tom features to define transformations and traversals and to obtain a new Gom term which can be transformed into a new Java class.

Predefined mapping

To support the analysis and transformation of Java bytecode programs, Tom provides several mappings:

• adt/bytecode/Bytecode.tom provides an abstract syntax tree implementation to represent any Java bytecode program. • adt/bytecode/_Bytecode.tom contains the congruence strategies associated to the AST.

• java/bytecode/cfg.tom defines new strategies that allows to explore the control flow graph.

Java classes as Gom terms

In order to represent bytecode programs, we have defined a Gom signature that allows us to represent any bytecode program by a typed term. Given a Java class, we use ASM to read the content and build an algebraic representation of the complete Java class. This approach is similar to BCEL. Contrary to ASM, this permits multi-pass or global analysis. This chapter documents important changes in the Tom language that impact running code.

We explain how to modify your programs in order to be able to use the last version of Tom.

Migration from 2. 6 to 2. 7 Tom

• by introducing conjunctions and disjunction of constraints we had to re-introduce the disjunction of constraints. To help debugging, the action-part are sometimes compiled into a single-line. Therefore, we recommend not using single-line comment (//) in '%match' and '%strategy' constructs. • Thus, disjunction of patterns which used to be written like:

Migration from 2. 5 to 2. 6 Tom

• the mapping can now be inlined. To activate this option (--inline and --inlineplus), the parameters of a mapping have to be prefixed by a '$'

• the antlrmapped has been removed and replaced by GomAntlrAdapter, see also this section.

• when defining a mapping, if no make is defined, a default one (corresponding to a function call) is automatically added. Since version 2.6, it is added only if no other mapping construct is defined.

Gom

• the Java code generated for list-operators is now implementing the Collection interface.

Therefore, the name Empty can non longer be used for a constructor, this would generate two isEmpty() methods.

Strategies

• the forward mechanism is no longer used. Hand written strategies have to be modified as explained in section Strategies.

• mustrategy.tom, mutraveler.tom, and strategy.tom have been removed. sl.tom has to be used instead.

Migration from 2. 4 to 2. 5 Gom

Representation of lists (FL). The default behaviour of lists is FL. The semantics has changed in case of associative symbol under an other associative symbol.

Gom syntax. The syntax compatibility with Vas is now not available.

Tom

The %rule has been removed. It can be replaced by rules hooks in Gom, described in Section Algebraic rules. The syntax for rules is unchanged, except that 'where' clauses are no more supported. Since rules are integrated into the code generated by Gom, it is no more possible to short-circuit rule application by calling Java functions instead of ''' to built terms.

Strategies

Call to MuTraveler.init should be removed

The backquote for the default strategy in %strategy could be removed.

Migration from 2. 3 to 2. 4

Builtins Since version 2.4, builtin sorts (int, long, String, etc.) are no longer implicit. The corresponding %include { ... } must be done explicitly.

Gom, Vas, and ApiGen

Since version 2.4, ApiGen and Vas are obsolete. Gom should be used instead.

Migration from 2. 2 to 2. 3 Mapping definition and term notation

To avoid ambiguities, since version 2.3, constants should be written using explicit parentheses: a(), nil(), for example. To be coherent, the parentheses have also to be used in the mapping definition: • in %oplist, get_head, get_tail, and is_empty have to be defined. In practice, these definitions have to be copied from %typelist to %oplist • in %oparray, get_element, and get_size have to be defined. In practice, these definitions have to be copied from %typearray to %oparray • %typelist, and %typearray do no longer exist: %typeterm has to be used to define any kind of sort. This is not a problem since access functions are now defined inside operator definitions (%op, %oplist, or %oparray) • get_fun_sym, cmp_fun_sym, and get_subterm do no longer exist in %typeterm

• fsym do no longer exists in %op, %oplist, and %oparray As an example, let us consider the following "old" mapping definition:

Variable

To prepare a future extension where variables have to be distinguished from constructors of arity 0, we have turned into error all ambiguities between variables and constructors. As a consequence, a variable cannot any longer have the same name as a constant.

Vas

Since version 2.2, ApiGen and Vas have been updated:

• name of list-operators defined in Vas are now significant and can be used in match constructs.

• generated Tom mappings are now stored in the same directory as the generated factory.

In practice, imports of the form %include{ file.tom } have to be replace by %include{ package/file.tom }.

Strategy library

The TravelerFactory class has been removed and replaced by a Tom mapping:

Migration from 2. 0 to 2. 1 Tom library

Since version 2.1, the runtime library has been reorganized. Java importations have to be updated according to the following hierarchy:

Using Eclipse IDE

The Eclipse platform (3.2 or newer) can be used to edit, compile, and run with Tom program. Eclipse is available for download at www.eclipse.org [9] .

Installation

Tom has to be installed using one of the previously described methods:

• simple Windows install: run tom-2.7_setup.exe

• manual install (Windows or Unix)

Use Ant to compile an example

Eclipse Plugin

In parallel to Tom, we also develop an Eclipse Plugin that integrates an editor and a compiler for Tom.

The plugin is available directly from the Eclipse platform via the update link:

• Help->Software Updates

• select Available Software, Add Site

Getting the sources

Command line

The Tom and Gom sources are available through anonymous svn(1). To get them, use the command: svn checkout svn://scm.gforge.inria.fr/svn/tom/jtom/trunk jtom Developer access is possible via ssh or DAV. See Gforge [1] for detailed instructions.

The svn checkout will get a new repertory in your current working directory, called jtom. We will call this directory ${TOM_BASE}.

Using Eclipse

• install subclipse [2] , 1.4.x for instance (see detailed instructions [3] ), providing support for Subversion within Eclipse • Window->Open Perspective->Other->SVN Repository Exploring

• New->Repository Location

• svn://scm.gforge.inria.fr/svn/tom (anonymous access)

• https:/ / scm. gforge. inria. fr/ svn/ tom (registered users)

• expand jtom and do a checkout on the trunk

• "checkout as a project in the workspace", call it jtom, click Finish Note: the Tom Eclipse Plugin cannot be used to compile Tom from the sources

Prepare for the build

Build the Tom distribution

The Tom build process uses apache ant [4] to automate the all parts of the process. This build process is specified by the ${TOM_BASE}/build.xml file.

Command line

You need to have apache apache ant [5] (1.7 or earlier) installed in order to compile Tom.

The Tom compiler

The Tom compiler is a non-intrusive pattern matching compiler. It takes a Tom program, combination of a host programming language (Java, C or Caml) extended by Tom constructs. Each Tom program can define its own data structures and manipulate them in order to write pattern-matching based algorithms.

Development process

As mentioned earlier, Tom generates host language code. The command tom invokes the compiler on a Tom source file and generates a new source file (with .java, .tom.c, or

.tom.ml extension, depending on the compilation command-line). The generated code has to be compiled/interpreted by a tool which can handle the corresponding host language:

javac for Java, cc for C and ocamlc for Caml.

A typical development cycle is the following:

• edit a Tom program (by convention, a Tom source code has the .t extension)

• run the Tom compiler on this file

• compile the generated file (javac file.java, or cc file.tom.c,…)

• execute the program (java file, or a.out,…)

Ant task

Gom can also be used within ant, and has its own ant tasks.

To use the Gom ant task, you have to first declare it the same way as the Tom ant task.

<taskdef name="gom" classname="tom.gom.tools.ant.GomTask" classpathref="tom.classpath"/>

Once the task is defined, you can use them to compile a Gom file.

The Gom ant task has to be able to find a configuration file for Gom. It can either use the tom.home property to find its configuration file, or use the value of the config attribute.

Since the tom.home property is also used when Gom has to process hooks, it is a good practice to always define the tom.home property to the installation path of the Tom system.

The default configuration file for Gom is included in the Tom distribution as Gom.xml.

<gom config="${gom.configfile}" srcdir="${src.dir}" package="example" destdir="${gen.dir}"> <include name="**/*.gom"/>

</gom>

Like in Tom example, in this Gom ant task we want to compile all Gom source files in {src.dir} and to configure the compiler to create a package called example in {gen.dir} for the generated code, just as we do for Gom in command line.

The Gom task takes the following arguments: The set of .gom files to compile is specified with a nested include element.

Gom Antlr adaptor

GomAntlrAdaptor is a tool that takes a Gom signature and generates an adaptor for a given Antlr grammar file. This way, Gom constructors can be directly used in the rewrite rule

Ant task

The GomAntlrAdaptor task takes the following arguments:

Compiling Tom under Vim

To compile Tom programs (like Tom) under Vim, and get a correct error reporting, you will have to set the ${CLASSPATH} environment value to the path of junit.jar, and use the makeprg variable to have :make call ant through a script maintaining the link between Tom and the generated Java files. We suppose here that Tom was installed in ${HOME}, i.e.

${TOM_HOME} is ${HOME}/workspace/jtom. let $CLASSPATH = "${HOME}/workspace/jtom/src/lib/tools/junit.jar" set makeprg=ant\ -find\ build.xml\ -emacs\ $*\\\|\ \ awk\ -f\ \"${TOM_HOME}/../../utils/ant-tom.awk\"

The provided awk script changes .java extensions into .t ones and removes gen/ from the file paths mentioned in the error messages. You may have to tune it to fit your needs.

Also note this is meant to be used with the POSIX version of awk (not the GNU one), although it may work out of the box on many configurations.

Shell Zsh

Zsh completion functions for Tom and Gom are available in the share/contrib/zsh directory. To install them, you only have to add those files to zsh's fpath variable.

For example, assuming you already set up the ${TOM_HOME} environment variable to the Tom installation directory, you can add to your ${HOME}/.zshrc: fpath=(${TOM_HOME} $fpath)

Build Tom projects using Ant

To build complex projects using Tom, it is useful to use Ant [2] as build system, to manage generation of data structure using Gom and the compilation of Tom and Java code.

To ease the use of Ant Tom server is an experimental way of running tom without paying the cost of the JVM and Tom library loading. It consists in a server that is meant to be run as a local deamon and a client that acts as the "tom" command.

Using Tom Server

• Install Jython ≥2.5b1

[1]

• [Optional] Change the PORT variable in $TOM_HOME/bin/tom-server.py and $TOM_HOME/bin/tom-client • Run the server: tom-server

• Compile your tom files as usual using the client: tom-client OPTIONS FILES Interfacing Tom with GNU Emacs' Flymake Flymake [2] is a feature of Emacs 22 that enables on-the-fly compilation a la Eclipse with little effort. Tom server is sufficiently quick to allow flymake to reasonably interoperate with tom. Here comes the mandatory screenshot [3] .

• Add the following lines to your .emacs (provided that you already have added jtom-mode.el to site-lisp) (require 'flymake) (autoload 'jtom-mode "jtom-mode" "jtom mode" t)

(setq auto-mode-alist (append '(("\\.t$" . jtom-mode))

auto-mode-alist))

(setq flymake-allowed-file-name-masks (cons '(".+\\.t$" flymake-simple-make-init flymake-simple-cleanup flymake-get-real-file-name) flymake-allowed-file-name-masks))

(add-hook 'jtom-mode-hook '(lambda () (if (not (null buffer-file-name)) (flymake-mode))))

• Add jtom/utils/tom-server/tom-flymake.py to your path