[antlr-interest] Building Treenodes from Kleene Closure

[Gavin Lambert]

At 07:07 20/02/2008, Dejas Ninethousand wrote:
>I think that's moving in the right direction, except I want the 
>seperators and not the expression.  I tried:
>
>expression (e+=EXPRESSION_LIST_SEPARATOR expression)* -> $e+ 
>EXPRESSION_LIST
>
>which works fine unless there are 0 occurences of 
>EXPRESSION_LIST_SEPARATOR expression in which case the parser 
>throws an early exit exception.  Is there a way to exclude the 
>$e+ if the number of occurrences is zero?

Yeah: $e*. :)

>I tried:
>
>expression_list
>     :
>     expression -> EXPRESSION_LIST
>     |
>     expression (e+=EXPRESSION_LIST_SEPARATOR expression)+ -> $e+ 
> EXPRESSION_LIST
>
>but ANTLER complains about introduction of left recursion (which 
>I don't see).

Can 'expression' include 'expression_list'?

But anyway, what you do have there is common left prefixes in 
alts, which isn't a good idea.  Try this instead:

expression_list
   :  expression -> EXPRESSION_LIST
      ( (e+=EXPRESSION_LIST_SEPARATOR expression)+ -> 
^(EXPRESSION_LIST $e+) )?
   ;

But it's a bit strange that you're throwing away all the actual 
expressions.