45 pair

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