Greetings!
On Sun, 2010-10-24 at 02:35 -0700, Trevor John Thompson wrote:
> I have a language in which one expression may immediately follow another. I
> am trying to construct an AST with an imaginary node representing the
> "concatenation" operator. I want the moral equivalent of
> expr: term (SP^ term)*;
> except that SP does *not* actually appear in the token stream.
> When i try
> expr: term (term->(^SP $expr term))*;
> i get RewriteEmptyStreamException in that rule on input like
> a b c
> Here is a tiny grammar that demonstrates the problem:
> grammar Test;
> options {output=AST;}
> prog: expr NL! EOF!;
> expr: term (term->^(SP $expr term))*;
> term: ID;
> fragment
> SP : ' '|'\t';
> ID : SP*
> ('a'..'z'|'A'..'Z'|'_'|'\u0080'..'\uFFFE')
> ('0'..'9'|'a'..'z'|'A'..'Z'|'_'|'\u0080'..'\uFFFE')*
> ;
> NL : ('\r'|'\n')+;
>
> I would appreciate anyone pointing out what i am doing wrong.
need to initialize the expr.tree before entering the loop, so try:
expr: (term->term) (term->^(SP $expr term))* ;
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