[antlr-interest] FYI Duplicate Nodes Behavior

[Bastian Asam]

Hello everybody,
I just spend almost a day to figure out a difference on how ANTLR handles 
the duplication of nodes and thought it might be helpful to others.

What I was trying to do is rather simple:

dup : 'test =' refs -> ^('test' refs refs) ;
refs : id(',' id)* ;
id : ID ;

That generates with input "test = test1,test2" this tree: ^('test' id 
test1 test2 ^(nil test1 test2))

Why is there a nil node generated?

My solution to this is to put the refs definition in the dup definition:
dup : 'test =' (i+=id(',' i+=id)*) -> ^('test' $i* $i*) ;       // don't 
forget the * !!
id : ID ;

Is not particularly beautiful, but works :)

Output is now
^('test' id test1 test2 test1 test2)

Hope this helps someone...
Bastian



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