[mercury-users] Operator precedence of =>

Fergus Henderson fjh at cs.mu.OZ.AU
Mon Feb 1 00:25:39 AEDT 1999


On 27-Jan-1999, Lee Naish <lee at cs.mu.OZ.AU> wrote:
> 
> Ralph Becket wrote:
> >I'm not sure about other people, but
> >I'd find it more natural (not to say, more convenient) to have the
> >following precedence order (from most to least tightly binding):
> >
> >	conjunction < implication < quantification
> >
> >rather than the current order
> 
> A bit of historical info:
> 
> I strongly suspect Mercury inherited its precedences from NU-Prolog,

This is entirely correct.

I agree with Ralph's suggestion -- I too find the current precedence
order annoying and I agree that the one Ralph suggests would be more
natural.

My only concerns are (1) backwards compatibility and (2) finding the
time to do it (there are a lot of other tasks which probably deserve
a higher priority).

Regarding (1), is there anyone here on the mercury-users mailing list
who has written any significant amount of code using implication or
explicit quantification?  Is there anyone who would be upset if we
simply changed the precedence for the next release, without making
any provision for backwards compatibility?  For some programs,
this could conceivably result in a silent change in the semantics,
but a compile error is the most likely result.

-- 
Fergus Henderson <fjh at cs.mu.oz.au>  |  "Binaries may die
WWW: <http://www.cs.mu.oz.au/~fjh>  |   but source code lives forever"
PGP: finger fjh at 128.250.37.3        |     -- leaked Microsoft memo.



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