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threads - nondet

This folder illustrates non-deterministic multi-threading calls and the use of tags to distinguish between multi-threading calls.

Print Logtalk, Prolog backend, and kernel versions (if running as a notebook):

%versions

Start by loading the example:

logtalk_load(nondet(loader)).

Mke a threaded call with a non-deterministic goal:

threaded_call(lists::member(X, [1,2,3])).

<!-- X = _G189. -->

Retrieve through backtracking all solutions for the non-deterministic goal:

%%table
threaded_exit(lists::member(X, [1,2,3])).

<!-- X = 1 ; X = 2 ; X = 3 ; false. -->

Make a threaded call by committing to the first solution found:

threaded_once(lists::member(X, [1,2,3])).

<!-- X = _G189. -->

Retrieve through backtracking the goal solution:

threaded_exit(lists::member(X, [1,2,3])).

<!-- X = 1 ; false. -->

When two or more variant calls are made...

threaded_call(lists::member(X, [1,2,3])), threaded_call(lists::member(Y, [1,2,3])).

<!-- X = _G189 Y =_G190. -->

...the first threaded_exit/1 call will pick one of them:

%%table
threaded_exit(lists::member(X, [1,2,3])).

<!-- X = 1 ; X = 2 ; X = 3 ; false. -->

...and a second threaded_exit/1 call will pick the remaining one:

%%table
threaded_exit(lists::member(X, [1,2,3])).

<!-- X = 1 ; X = 2 ; X = 3 ; false. -->

Tags may be used to distinguish between threaded calls if needed:

threaded_call(lists::member(X, [1,2,3]), Tag).

<!-- Tag = 1. -->

threaded_call(lists::member(X, [1,2,3]), Tag).

<!-- Tag = 2. -->

%%table
threaded_exit(lists::member(X, [1,2,3]), 2).

<!-- X = 1 ; X = 2 ; X = 3 ; false. -->

Use a subsumed goal instead of a variant of the original goal:

threaded_call(lists::member(X, [1,2,3,2])).

<!-- X = _G189. -->

threaded_exit(lists::member(2, [1,2,3,2])).

<!-- More ; More ; false. -->