[antlr-interest] On to the next issue: error(211)

[Hendrik Maryns]

Gavin Lambert schreef:
> At 01:52 12/11/2008, Hendrik Maryns wrote:
>  >The thing I am having trouble with is that, with the idea of
>  >polymorphism etc., I'd like to have things dealt with at the
>  >appropriate place.
>  >
>  >I have rules like
>  >
>  >atomic : atomicHead variable label ;
>  >
>  >atomicHead : EQUALITY | DOMINANCE | INCLUSION | … ;
>  >
>  >and depending on the value of atomicHead, I 
> want a different Java
>  >object to be created.
> 
> If you have input AST fragments like this:
>    ^(EQUALITY a b)
>    ^(DOMINANCE a b)
>    ^(INCLUSION a b)
>    ^(INVERSE a)
> 
> then they're trivial to parse with AST 
> rules.  The job of the parser is usually to 
> translate the sequential token stream into a tree 
> structure that conveys the intended meaning; the 
> tree parser then goes through that tree and does 
> whatever you want.

That is what I intended to do, but the problem remains.  Indeed I will
have to come back from the generalization that I had in the atomic rule,
and indeed just list all possible subtypes separately, each of them
looking for their arguments.  This is no problem, but I just thought it
was a nice generalization.  For simple parsing, it works, but it makes
it difficult to generate the proper code, due to the dependencies on
subrules.

  The tree grammar is usually
> very simple and you should almost never need to 
> use any predicates in it.

I see.  Since my grammar is so easy, I will do it in the parser directly
instead.


> (Though I'm not sure why you're calling this 
> "atomic".  It seems like an odd choice of name 
> for something that seems to require neighbouring symbols as well.)

Lol, because they are atomic formulas in the problem domain, but of
course not viewn from a parser standpoint.

>  >I cannot do
>  >
>  >atomic return [Formula result] : atomicHead[$variable.result,
>  >$label.result] variable label { $result = $atomicHead.result; };
>  >
>  >since $variable.result and $label.result will not have been
>  >evaluated at that point.
> 
> atomic returns [Formula result]
>    : ^(EQUALITY variable expr) { $result = new
>          Equality($variable.result, $expr.result); }
>    | ^(DOMINANCE ...

So indeed split up the rule which generalizes over the structure of the
several atomic formulas (head variable variable) into a rule for each
head.  This is what I am doing now.

Thanks!

H.
-- 
Hendrik Maryns
http://tcl.sfs.uni-tuebingen.de/~hendrik/
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