[antlr-interest] Token Stream Rewriting

[Fabien Hermenier]

Hi

I have some troubles with token stream rewriting. Below is the piece of 
ANTLR code. I have a grammar, with an AST as output and Java
as the target. I want to insert a sequence of token into the stream.

I have followed the page 
http://www.antlr.org/wiki/display/~admin/2007/06/28/Token+stream+rewriting+with+rewrite+rules 
and adapted the example that interest me. A piece of the code is 
following. Basically, in the alternative of 'explodedSet', I get the 
return values of other rules and do some stuff in the merge method. This 
one returns a list of String as explained in the online example.


explodedSet: '{' (setContent (',' setContent)*)? '}' -> ^(EXPLODED_SET 
setContent+)
     | {List l = new LinkedList();}LEFTY 
r1=brace_content{l.add($r1.ret);} (',' 
r2=brace_content{l.add($r2.ret);})* RIGHTY
     -> {
     merge($LEFTY.text,l,$RIGHTY.text)
     };

brace_content returns [List ret]:
          st=number ('..' ed=number)? {$ret = new LinkedList(); for (int 
i = $st.val; i <= $ed.val; i++) {$ret.add(i);}}
            | NAME {$ret = new LinkedList(); $ret.add($NAME.text);};

The code compiles well but at runtime, I've got this exception:

Caused by: java.lang.ClassCastException: java.util.ArrayList cannot be 
cast to org.antlr.runtime.tree.Tree
     at 
org.antlr.runtime.tree.BaseTreeAdaptor.addChild(BaseTreeAdaptor.java:107)
     at Parser.explodedSet(Parser.java:560)

So, the return value of merge does not seems to be converted into tokens 
nor Tree. Does someone has an idea ?


Fabien.