[antlr-interest] Rewrite rules, again!

Terence Parr parrt at cs.usfca.edu
Thu Mar 13 17:01:02 PDT 2008


You need to alter the parse to associated things right to left.   
(...)* associates left to right.

Something like:

assign : expr '=' x ;

x : assign
    | expr
    ;

note that this is how grammars to ^ exponent operators...look for a  
rule that does that.
Ter

On Mar 13, 2008, at 3:32 PM, Shaun Bogan wrote:

> I got some great help creating the following for my grammar:
>
> assignops :
> (boolops->boolops)(firstops b2=boolops -> ^(OPERATOR ^(firstops
> ^(OPERAND $b2) ^(OPERAND $assignops))))*
> ;
>
> To make the above clear, it is basically just:
> assignops :
>    boolops (firstops boolops)*
>    ;
> with rewrite rules.
>
> The problem is this creates an AST that groups items in the reverse of
> how I need them.  For example:
> a = b = c;
> will create a tree that my tree walker (doing depth first) would  
> evaluate as:
> (a = b) = c;
>
> This is obviously wrong.  It should be a = (b = c);
>
> Essentially, my parse tree looks fine, but I can't figure out how (if
> there is a way) to get my rewrite rule to write my AST like above.
>
> Any help is greatly appreciated,
> Shaun M Bogan



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