[antlr-interest] rewriting tree such that children are at same level

[David-Sarah Hopwood]

hakan eryargi wrote:
> hello,
> 
> below is the main part of my grammar. it's ok but it creates an AST
> from expression
> 
> a & b & c  -> (& (& a b) c) : an AND node with children c and another
> AND node with children a and b
> 
> but i want: (& a b c) : an AND node with tree children
> 
> how can i make that with a rewrite rule ?
> 
> i've found following post in mail list but didnt helped me much :/
> http://markmail.org/message/ed3ncmfimu3xnczt
> 
> program :
> 	expression EOF!
> 	;
> 
> expression
> 	: primary ((AND^ primary)+ | (OR^ primary)+)?
> 	;

Change this to (tested):

  expression
        : primary (                -> primary
                  | (AND primary)+ -> ^(AND primary+)
                  | (OR  primary)+ -> ^(OR  primary+)
                  )
        ;

This works because the 'primary+' on the right-hand-side of
each '->' includes all primary nodes matched in the overall
production.

The other replies you got suggesting to use += may also work,
but the solution above is simpler; normally you only need to
use += if you need to refer to the list of nodes in an action.

Jim Idle wrote:
> Not sure WHY you would want that buy it is just:
> 
> p+=primary (AND p+=primary)* -> ^(AND $p+)

I assume that the solution still needs to satisfy the requirement
in the recent thread with subject "forcing parenthesis":
<http://www.antlr.org/pipermail/antlr-interest/2009-July/035196.html>
<http://www.antlr.org/pipermail/antlr-interest/2009-July/035248.html>

-- 
David-Sarah Hopwood  ⚥  http://davidsarah.livejournal.com