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59 lines
1.6 KiB
Mathematica
59 lines
1.6 KiB
Mathematica
%---------------------------------------------------------------------------%
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% vim: ft=mercury ts=4 sw=4 et wm=0 tw=0
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%---------------------------------------------------------------------------%
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% Copyright (C) 1994-2006 The University of Melbourne.
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% This file may only be copied under the terms of the GNU Library General
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% Public License - see the file COPYING.LIB in the Mercury distribution.
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%---------------------------------------------------------------------------%
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%
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% File: pair.m.
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% Main author: fjh.
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% Stability: high.
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%
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% The "pair" type. Useful for many purposes.
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%
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%---------------------------------------------------------------------------%
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%---------------------------------------------------------------------------%
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:- module pair.
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:- interface.
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:- type pair(T1, T2)
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---> (T1 - T2).
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:- type pair(T) == pair(T, T).
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:- inst pair(I1, I2)
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---> (I1 - I2).
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:- inst pair(I) == pair(I, I).
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% Return the first element of the pair.
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%
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:- func fst(pair(X, Y)) = X.
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:- pred fst(pair(X, Y)::in, X::out) is det.
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% Return the second element of the pair.
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%
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:- func snd(pair(X, Y)) = Y.
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:- pred snd(pair(X, Y)::in, Y::out) is det.
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:- func pair(T1, T2) = pair(T1, T2).
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%---------------------------------------------------------------------------%
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%---------------------------------------------------------------------------%
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:- implementation.
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fst(X - _Y) = X.
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fst(P, X) :-
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X = fst(P).
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snd(_X - Y) = Y.
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snd(P, X) :-
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X = snd(P).
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pair(X, Y) = X - Y.
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%---------------------------------------------------------------------------%
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:- end_module pair.
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%---------------------------------------------------------------------------%
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