tom-2.8:Migration Guide

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Tom-2.8 : Language Reference

Tom  > Gom  > Strategies  > Runtime Library  > Migration guide  > EMF

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 2.7 to 2.8


  • anonymous operators are no longer allowed in patterns. You have to explicitly give the name.


  • the old production grammar syntax (Op(...) -> Sort) is no longer supported


  • flag --grammar no longer exist
  • the name for the generated file <grammar>TokenList.txt has been renamed into <grammar>Tokens.tokens

Migration from 2.6 to 2.7


  • 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:
%match(l) {
  p1 | p2 -> { ... }

can now be written:

%match(l) {
  p1 || p2 << l -> { .. }


  • the old syntax using keyword sorts, compatible with vas is no longer maintained
  • we introduced a new function: getCollection<opname>(), which converts (when possible) a Gom list into a collection, such that for-each loop can be used (for(Term x:l.getCollectionconc()) { ... } for instance)
  • renamed the option --strategies-mapping (resp. -sm) into --withCongruenceStrategies (resp. -wcs)


  • the public interface of Position has changed:
    • use Position.make() instead of new Position()
    • use Position.makeFromArray() instead of new Position(int[])
    • use Position.makeFromPath() instead of new Position(Path)
    • ...
    • use length() instead of depth()
    • setValue(int[]) has been removed

Migration from 2.5 to 2.6


  • 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.


  • 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.


  • 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


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.


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.


%include { mustrategy.tom } should be replace by %include { sl.tom }

Any reference to jjtraveler or tom.library.strategy.mutraveler should be replaced by a reference to

  • replace import tom.library.strategy.mutraveler.*; by import*;
  • replace import jjtraveler.*; by import*;
  • replace jjtraveler.Visitable by
  • replace jjtraveler.VisitFailure by
  • replace jjtraveler.Visitor by
  • replace jjtraveler.reflective.VisitableVisitor by
  • replace MuStrategy by Strategy

getPosition() should be replaced by getEnvironment().getPosition()

apply(...) should be replaced by visit(...) or visitLight(...), enclosed by a try ... catch(VisitFailure e) ...

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


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:

%op T a() {

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:

%op T f(arg1:T, arg2:T) {
  get_slot(arg1,t) { get_subterm(t,0) }
  get_slot(arg2,t) { get_subterm(t,1) }
  • for each operator (%op, %oplist, and %oparray), the is_fsym(t) predicate has to be defined. This function should return true when t is rooted by the considered symbol, and false otherwise. In practice, the constructs can be deduced by combining get_fun_sym, cmp_fun_sym, and fsym:
%op T f(arg1:T, arg2:T) {
  is_fsym(t) { cmp_fun_sym(get_fun_sym(t), body of the old fsym construct) }
  get_slot(arg1,t) { get_subterm(t,0) }
  get_slot(arg2,t) { get_subterm(t,1) }
  • 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:

%typeterm TomTerm {
  implement          { ATermAppl        }
  cmp_fun_sym(t1,t2) { t1 == t2         }
  get_fun_sym(t)     { t.getName()      }
  get_subterm(t, n)  { t.getArgument(n) }
  equals(t1, t2)     { t1 == t2         }
  %typelist TomList {
  implement          { ATermList               }
  get_fun_sym(t)     { ((t instanceof ATermList)?"conc":null) }
  cmp_fun_sym(t1,t2) { t1 == t2                }
  equals(l1,l2)      { l1 == l2                }
  get_head(l)        { (ATermAppl)l.getFirst() }
  get_tail(l)        { l.getNext()             }
  is_empty(l)        { l.isEmpty()             }
  %op TomTerm a {
  fsym   { "a" }
  make() { factory.makeAppl(factory.makeAFun("a", 0, false)) }
  %op TomTerm f(TomTerm) {
  fsym     { "f" }
  make(t1) { factory.makeAppl(factory.makeAFun("f", 1, false),t1) }
  %oplist TomList conc( TomTerm* ) {
  fsym             { "conc"             }
  make_empty()     { factory.makeList() }
  make_insert(e,l) { l.insert(e)        }

The two first type definitions have to be replaced by:

%typeterm TomTerm {
  implement      { ATermAppl }
  equals(t1, t2) { t1 == t2  }
  %typeterm TomList {
  implement     { ATermList }
  equals(l1,l2) { l1 == l2  }

The operator definition can be replaced by the following code:

%op TomTerm a {
  is_fsym(t) { t.getName() == "a" }
  make()     { factory.makeAppl(factory.makeAFun("a", 0, false)) }
  %op TomTerm f(arg:TomTerm) {
  is_fsym(t)      { t.getName() == "f" }
  get_slot(arg,t) { (TomTerm) t.getArgument(t,0) }
  make(t1)        { factory.makeAppl(factory.makeAFun("f", 1, false),t1) }
  %oplist TomList conc( TomTerm* ) {
  is_fsym(t)       { t instanceof ATermList }
  get_head(l)      { (ATermAppl)l.getFirst() }
  get_tail(l)      { l.getNext() }
  is_empty(l)      { l.isEmpty() }
  make_empty()     { factory.makeList() }
  make_insert(e,l) { l.insert(e) }

Disjunction of patterns

Since version 2.2, the disjunction of patterns construct has become deprecated. It can still be used, but we recommend to use the disjunction of symbols instead. This last construct allows to share patterns which have similar subterms but different head-symbols. Therefore, the construct g(g(a)) ∣ g(h(a)) can be replaced by g( (g ∣ h)(a) ). Since version 2.2, this construct has been extended to support disjunction of symbols which do not have identical signature: only involved slots have to be compatible.

Considering %op T f(arg1:T, arg2:T) and %op T g(arg1:T), it is now possible to write g( (g ∣ f)[arg1=a] ).


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.


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: mutraveler.tom. Therefore, backquote notation has to be used: travelerFactory.Repeat(travelerFactory.OnceBottomUp(rule)) is replaced by ‘Repeat(OnceBottomUp(rule)).

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:

     +--- library
     |        +--- adt               (datatype definitions)
     |        +--- mapping           (predefined mapping)
     |        |      +--- adt        (generated mapping)
     |        +--- plugin            (platform tools)
     |        +--- set               (to handle sets)
     |        +--- strategy
     |        |      +--- concurrent (to support parallel strategy)
     |        +--- traversal         (generic traversal)
     |        +--- xml               (xml tools)
     +--- platform                   (the Tom Plugin Platform, known as Tom server)
              +--- adt

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).

Language Reference

Tom  > Gom  > Strategies  > Runtime Library  > Migration guide  > EMF

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