french.logic

国外的一套开源CRM

/*
Here is a simple example of lists.
Try the query:
    ok(N, A, B)
which should produce the result:
    N = 1.0, A = dark, B = full
    N = 2.0, A = continental, B = viennese
    N = 3.0, A = dark, B = [full, high, viennese, continental]
    N = 4.0, A = viennese, B = continental
    N = 5.0, A = viennese, B = [continental]
    no more results
*/

french(["dark", "full", "high", "viennese", "continental"]);

ok(N, A, B) :- #(N, 1), french([A, B, C, D, E]);
ok(N, A, B) :- #(N, 2), french([E, D, C, B, A]);
ok(N, A, B) :- #(N, 3), french([A | B]);
ok(N, A, B) :- #(N, 4), french([C, D, E | [A, B]]); 
ok(N, A, B) :- #(N, 5), french([C, D, E | [A | B]]);

// these fail:
ok(N, A, B) :- #(N, -1), french(A, B, C, D, E);
ok(N, A, B) :- #(N, -2), french([A, B]);