Say I’m doing some list processing in the usual way: process([X|Xs], Acc, Final) :- do_work(X,Y), !, process(Xs, [Y|Acc], Final). process([], Final Final). I want to put together a chain like this: process(In, [], Out1), process(Out1, [], Out2), process(Out2, [], Final), foldl(do_more_work, Fi…

The problem there is that the source (random) is not a list, and the outputs do not chain lists. Both of these things are an issue for my use case. Here is something that works for me it seems: do_work([], [], 0) :- false, !. do_work([X|Xs], Xs, Final) :- Final is X + 1. test(Total) :- lazy_l…

Last thing I need is to be able to chain things which do not return 1-for-1 lists. For example, say at the top I insert [1,2,3] and the next process creates [4,5,6,7,8,9] from that input. I dont see an obvious way to do that with lazy lists or otherwise.

I’ve got what i need working with lazy_list except its useless for the purpose since its about 20x slower than a fully materialized version. I had the same experience when using lazy_findall/3.

Sorry about the long reply :smiley: [image] emiruz: Say I’m doing some list processing in the usual way: process([X|Xs], Acc, Final) :- do_work(X,Y), !, process(Xs, [Y|Acc], Final). process([], Final Final). This way you show is slightly unusual. It is impossible to tell without a concre…

[image] emiruz: I’ve got what i need working with lazy_list except its useless for the purpose since its about 20x slower than a fully materialized version. I assume you know that SWI Prolog lazy lists are implemented as constraints using attributed variables, and that unification of attribut…

Note that several of the predicates involving lazy lists have a chunk size argument or option. That reduces the number of wakeups. Still, there is quite a bit of work involved in extending the lazy list.

Thanks, no I didn’t know any of those things, but it all makes sense now.

Here is an example of me trying to use lazy lists to solve an AoC2024 problem. Ironically the memory blows up at the default limit, I’ve no idea why. % 353,135,695 inferences, 32.161 CPU in 32.171 seconds (100% CPU, 10980304 Lips) ERROR: Stack limit (1.0Gb) exceeded ERROR: Stack sizes: local: 2Kb…

The lazy_list abstraction is practical. It’d be great if you could write something using a similar contract which can be used to pipe lists into processes and processes into each other via lists. I’m not really sure how memoisation fits into all this, but I think its strange that a lazy list ends u…

Lazy processing

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Lazy processing

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