Re: findall

On Sun, 17 Feb 2008 07:33:07 -0800, Mark Tarver wrote:

Can findall be efficiently implemented in pure Prolog?

The answer depends on what you consider as pure Prolog - and what you
still consider efficient.

In Prolog with assert and retract, it is possible, actually, that's how
it has been done many times (sometimes with a variant of assert, named
record).

Without assert and retract (or any other magic [*]) the full
semantics of findall is impossible to implement, AFAIK, even if you
give up on efficiency.

[*] e.g. "engines"

You can do something that has the findall flavour in almost pure Prolog
(you need cut or if-then-else) when you just want all different answers,
without their multiplicity.

What is the origin of your question ?

Cheers

Bart Demoen
.

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