Stratego uses terms to represent the abstract syntax of programs or documents. A term consists of a constructor and a list of argument term. Sometimes it is useful to record additional information about a
term without adapting its structure, i.e., creating a constructor with additional arguments. For this purpose
terms can be annotated. Term annotation has the syntax
t1 { t2 }
where term
t2 is the annotation of term
t1. By making the annotation a list, any number of annotations
can be attached to a term. The annotations of a term can be retrieved in a pattern match and set in
a build. For example, the following rule checks that the two subterms of the
Plus have annotation
Int
and then attaches the annotation
Int to the whole term:
TypeCheck :
Plus(e1{Int}, e2{Int}) -> Plus(e1, e2){Int}
Naturally, annotation matching and building can be done in the match
?t and build
!t constructs.
Also congruences over annotations are supported. Thus, if
s1 and
s2 are strategies, then
s1{s2}
is also a strategy, which applies
s1 to the term and
s2 to its annotation.
The
GenericTermTraversal operators preserve annotations.
Support for
TermAnnotations has been available from
StrategoRelease07.
--
EelcoVisser - 07 Mar 2002
CategoryToDo? |
LanguageExtensions