[mercury-users] Pred defns
rwab1 at cam.sri.com
Fri Apr 3 18:57:24 AEST 1998
Fergus Henderson wrote on 3 Apr:
> Actually, it would make more sense to write "..., $foo,$, ..."
> rather than "..., $,$foo, ...".
> So how about if a single unadorned "$" in an argument list refered
> to the next state of the accumulator in the previous argument.
> update($foo, $, $bar, $), % you can insert spaces after all
> update($foo, $, $bar, $), % the commas, if you prefer
Oh dear God no! We're going to end up with Perl!
If we're going to have explicit accumulator naming, how about this?
:- pred p(...) + [a, b, c]. % + Accumulators in the head.
p(...) + [p, q, r] :- % + Local accumulators.
a = !a + 1,
p = 2,
q = !p + !a,
mimicing the dereferencing operator ! of ML. `!a' denotes the current
value of acc. a while plain `a' denotes the `next' value.
If we're going to have this facility at all I strongly feel that it
should look simple and *elegant*!
Time for my anti-aesthetics pill...
Ralph Becket | rwab1 at cam.sri.com | http://www.cam.sri.com/people/becket.html
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