On Thursday 22 December 2005 21:41, Bart Demoen wrote:
> The fact that findall/3 is perceived as inefficient is more of a
> historic (Prolog) implementation accident than a necessity anyway.
Besides its inefficiency there is also the problem of copying (or not).
Whereever we have mutable terms or attributed variables this is quickly
a more severe problem than simple space/time inefficiency,
Consider list processing as
findall(Y, (member(X, L), map(X, Y)), Ys)
vs
maplist(map, L, Ys)
I see many cases where the first is used while the second is intended.
These constructs differ in copying as well as non-determinism handling
of map/2. Not easy to explain ...
One also commonly finds constructs as this:
findall(X, Goal, Xs),
member(X, Xs),
...
I think there is a bit of teaching to do on when to use lists as
(answer-)sets and when to use non-determinism.
Cheers --- Jan
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