[antlr-interest] [bug?] AST rewrite rule with no (imaginary) token yields C runtime compile error

[David Benn]

Hi Gary

Thanks, that seems quite reasonable. Mostly I wanted to raise the  
question: should this error make it through to the generated parser  
code, or be caught by the ANTLR AST rewrite mechanism? If it is an  
illegal construct, I would suppose the latter.

Thanks.

Rgds,

DJB

On 30/05/2008, at 5:44 PM, Gavin Lambert wrote:

> At 20:07 30/05/2008, David Benn wrote:
> >predefined_type_def
> >                  : primitive_type -> ^(primitive_type)
> >                  | IDENT IDENT -> ^(IDENT IDENT)
> >                  ;
> >
> >i.e. it had no imaginary root node in the AST rewrite rule.
> [...]
> >Assuming the rewrite rule is legal (but perhaps not desirable), I
> >guess this is a bug in the C runtime code generation step.
>
> I vaguely remember a discussion on something similar a while back.   
> I think the general idea was that this sort of thing isn't legal,  
> since 'primitive_type' might expand to zero or more tokens, and  
> exactly one token must be the root node.
>
> You could always just not try to wrap it into another subtree level  
> though -- 'primitive_type -> primitive_type' should work fine.  (In  
> fact I think just 'primitive_type' alone should also work, but I  
> vaguely recall something odd with that as well.)
>

Regards,

David Benn
dbenn at computer.org
0407 261163

"The real voyage of discovery consists not in seeking new landscapes  
but in having new eyes." (Marcel Proust)