[antlr-interest] still more => wars ;)

[Terence Parr]

On Dec 8, 2005, at 3:07 PM, Martin Probst wrote:

>> Hmm...the two kinds of sem preds are pretty similar this way.  I do
>> like the => implies predicate though.  I wonder what we could do to
>> indicate gated.  Loring's original suggestion was
>
> Something missing here?

Sorry...I meant: ({...}?)=>

>> which is verbose but these are not used much and it's clear what we
>> mean w/o new syntax.  We could then do
>>
>> (...) => 	syntactic predicate
>> {...}?		_hoisting_ disambiguating semantic predicate
>> ( {...}? ) =>  gated semantic predicate
>
> Well, 7 special characters for the semantic predicate is certainly
> verbose

Yes, but I suspect you'll not need a gated pred very often.  Less  
then once a grammar.

> , but in my opinion not more accessible.

Well, it's an idiom rather than explicit syntax.  It does mean what  
we say though: fail if the predicate fails.  Note that it is a valid  
syntactic predicate.

> Plus it probably doesn't
> mean much to new users. Plus there hoisting semantic predicates get  
> the
> syntax which is now used for semantic predicates, which are closer to
> gated ones, or not? Is there purpose in there?

Yes, but hoisted is what we want; we just don't have them in v2.   
Normally you'll do the terse {...}?.

I'm not in love with the ({...}?)=> but it doesn't require new syntax  
at all.

Ter