[m-dev.] Assocative predicates
pets at students.cs.mu.OZ.AU
Thu Apr 23 11:36:24 AEST 1998
On Thu, 16 Apr 1998, Fergus Henderson wrote:
> How about just `pragma assert(Goal)'?
> :- pragma assert(all [A,B,C] (A+B)+C=A+(B+C)).
> :- pragma assert(all [A,B,C,D,E,F,G,H] (
> foo(A, B, C, D, E), foo(D, E, F, G, H) <=>
> foo(A, B, F, D, E), foo(D, E, C, G, H))).
> This syntax seems to be nice, at least from the user's perspective.
The generality and straight-forwardness of your proposal is certainly
appealing. I'd like to see implicit quantifiers, but your recent mail
cleans that up rather nicely.
However, I still think there is something to be said for using words people
recognize like "associative," "commutative," etc. I suppose that can be
done in comments, but how about allowing users (and the standard library) to
define properties. Maybe something like
:- pragma assertion(associative_function(F) = (F(A,F(B,C)) = F(F(A,B),C))).
:- pragma assertion(associative_predicate(P) = (
P(A,B,C), P(C,D,E) <=> P(B,C,F), P(A,F,E)
:- pragma assert(associative_function(+)).
:- pragma assert(associative_predicate(append)).
Better still, perhaps the overloading resolution mechanism could be used to
avoid the need for the `_function' and `_predicate' suffixes.
-Peter Schachte | The secret of being miserable is to have the
mailto:pets at cs.mu.OZ.AU | leisure to bother about whether you are
http://www.cs.mu.oz.au/~pets/ | happy or not. The cure is occupation.
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