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61 lines
1.2 KiB
Mathematica
61 lines
1.2 KiB
Mathematica
%---------------------------------------------------------------------------%
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% vim: ts=4 sw=4 et ft=mercury
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%---------------------------------------------------------------------------%
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:- module unsatisfiable_constraint.
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:- interface.
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:- import_module io.
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:- pred main(io::di, io::uo) is det.
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:- implementation.
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:- import_module int.
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:- import_module string.
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main(!IO) :-
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io.write_string("test(1): ", !IO),
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( if test(1) then
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io.write_string("yes\n", !IO)
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else
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io.write_string("no\n", !IO)
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),
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io.write_string("test(2): ", !IO),
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( if test(2) then
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io.write_string("yes\n", !IO)
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else
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io.write_string("no\n", !IO)
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).
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:- typeclass a(A, B, C, D) <= ((A -> B), (C -> D)) where [
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func f(A, C) = B,
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func g(A) = C
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].
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:- typeclass b(A, B) <= (A -> B) where [
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func h(A) = B,
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func ii = A
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].
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:- pred test(A) <= (a(A, B, C, D), b(B, C)).
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:- mode test(in) is semidet.
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test(A) :-
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B = g(A),
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C = h(B), % unsatisfiable!
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f(A, C) = ii.
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:- instance a(int, int, int, int) where [
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(f(M, N) = M + N),
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(g(M) = -M)
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].
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:- instance a(int, int, string, int) where [
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(f(M, S) = M + length(S)),
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(g(_) = "")
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].
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:- instance b(int, int) where [
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(h(N) = -N),
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(ii = 2)
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].
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