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40 lines
1.0 KiB
Mathematica
40 lines
1.0 KiB
Mathematica
%---------------------------------------------------------------------------%
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% vim: ts=4 sw=4 et ft=mercury
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%---------------------------------------------------------------------------%
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:- module mpj_3.
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:- interface.
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:- typeclass coll(E, C) <= (C -> E) where [
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func i(E, C) = C
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].
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:- type intlist
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---> []
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; [int | intlist].
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:- type stringlist
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---> []
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; [string | stringlist].
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:- func g(intlist) = intlist.
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:- implementation.
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% Error: overlapping instances:
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%
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:- instance coll(int, intlist) where [ (i(N, L) = [N | L]) ].
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:- instance coll(string, stringlist) where [ (i(S, L) = [S | L]) ].
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:- instance coll(string, intlist) where [ (i(_S, L) = [1 | L]) ].
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% Error: conflicting types for args 1 and 2, both of which are
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% determined by the type of L.
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%
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g(L) = f(1, "foo", L).
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% This probably should be an error, or at least a warning, since the
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% constraints could be tighter.
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%
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:- func f(A, B, C) = C <= (coll(A, C), coll(B, C)).
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f(A, B, C) = i(A, i(B, C)).
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