Re: STILL NOT RIGHT, <commit> and subrules

Actually, after looking at this further, this is still
not what I need.  Note that any subrule with a
repetition specifier is going to attempt to backtrack
if it fails on its last repeated attempt since it
assumes that text must be something else if it does
not match.  So, even though you can get it to fail by
anchoring it with a negative lookahead after it or
with your technique Marcel, any <error?> <reject>
production within the repeated rule after a commit is
useless, because of the backtracking.  IE. if the
repeated rule can be successful by backtracking by 1
match, that rule's queued error messages are
automatically discarded.  

Therefore, using the <commit> directive along with the
<error?> directive here is broken.  If you guys have
any other suggestions, let me know.  Maybe Damian, you
could enable a <commit> directive to propagate up the
rule stack so it forces a failure of the parse?  Since
your primary use of <commit> was to prune the parse,
maybe another directive like <hard_error?> could be
used to force the failure of the rule and all of its
calling parents regardless of any repetition
specifiers?  :)

Dave Mc



--- Marcel Grunauer <[email protected]>
wrote:
> On Donnerstag, Februar 7, 2002, at 02:14  Uhr,
> damian wrote:
> 
> > Usually by "anchoring" the end of the match. That
> might be:
> >
> >   myrule: 'stuff' mysubrule(?) ...!ID
> 
> it seems necessary to return a { 1 } here, as the
> rule
> fails otherwise, presumably because of the negative
> lookahead:
> 
>    myrule: 'stuff' mysubrule(?) ...!ID { 1 }
> 
> >   mysubrule: ID <commit> '[' ']'
> >            | <error?> <reject>
> >
> > or
> >
> >   myrule: 'stuff' mysubrule(?) /\s*\Z/
> >
> >   mysubrule: ID <commit> '[' ']'
> >            | <error?> <reject>
> >
> >
> > or whatever addition confirms that there really
> wasn't anything else
> > after 'stuff'.
> 
> another option would be the use of a rulevar:
> 
>    myrule : <rulevar: local $failed>
>    myrule : 'stuff' mysubrule(?) <reject:$failed>
> 
>    mysubrule: ID <commit> '[' ']'
>             | <error?> { $failed++ }
> 
> this way you don't have to specify a potentially
> complex negative
> lookahead, and the method works over several levels
> of subrules
> as well.
> 
> marcel
> 
> 


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