[mercury-users] correction

[Ralph Becket]

William Pippin wrote on 26 Mar:
> 
> that DCGs are not limited to lists.  Yes, I should have remembered
> that, from Craft of Prolog.
> 
> I'm still interested in using any number of named acc-pairs.

I have to say here that I found the business of named state threads a
la Peter van Roy's package actually obscured what was going on in
predicates - although I'm willing to admit that maybe I didn't give it
enough of a go.

I rather like Prolog's simple syntax and it's only occasionally that
it gets in the way.  There's a fine balance between too much and too
little here.

DCGs are, IMHO, too little: many predicates have more
than one state thread and very often one mixes `threaded' and
unthreaded predicates in the same clause, leading to a C of braces (to
coin a phrase).  Ugly if you do and ugly if you don't.

Externally named state threads add a fair whack of extra syntax (all
this :: and with and -->> and := and ...) and separate detail from the
clause (which is what they were intended for).

I'm still in favour of my eariler suggestion (X` and X``).  But it
could be a bad case of NIH syndrome...

Ralph

-- 
Ralph Becket  |  rwab1 at cam.sri.com  |  http://www.cam.sri.com/people/becket.html