[antlr-interest] Previous rule element reference in a scope

Graham Mer gd.antlr at gmail.com
Wed Apr 13 02:29:22 PDT 2011


Hello list,

I have a grammar that includes a "With" statement like the following:

With anObject
 .method1()
 .method2()

which is semantically equivalent to the following fragment:

anObject.method1()
anObject.method2()


During AST construction, I want to distribute 'anObject' to its
subordinate method calls, so that I get a tree like the following:

^(CALL anObject.method1)
^(CALL anObject.method2)

This is a natural fit for a scope, but I'm not sure how to capture the
'anObject' reference in a scope.

If I have a recognizer grammar with the following rules, how do I
capture the withStatement  ID in a scope, and how do I insert that
reference into the AST generated by memberCallStatement?

withStatement
 scope{ // what do I store here to save my ID? }
 :  'With' ID
 ;

memberCallStatement
 :  '.' ID '()'  // how do i insert $scope::ID in my AST?
 ;

Also, are there any special precautions I need to take to avoid
inserting loops in the AST, for example, do I need to make a new
instance of the with object every time I duplicate it in the AST, or
can I just re-use it? Is it best to use a String or my own Java
object, or can I capture the thing that the recognizer generates
directly?

I wish I could do essentially the following:

withStatement
 scope{ Object id; }
 :  'With'! id=ID!
 ;

memberCallStatement
 :  '.' ID '()'  -> ^(CALL $withStatement::id '.' $ID)
 ;

I know that will give ANTLR a sad, but I hope it illustrates what I
want to produce.


Thanks.


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