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23 enum

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% vim: ft=mercury ts=4 sw=4 et wm=0 tw=0
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% Copyright (C) 2000, 2005-2006 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.
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%
% File: enum.m.
% Author: stayl.
% Stability: medium
%
% This module provides the typeclass `enum', which describes types
% which can be converted to and from integers without loss of information.
%
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:- module enum.
:- interface.

    % For all instances the following must hold:
    %   all [X] (X = from_int(to_int(X)))
    %   all [Int] (some [Y] Int = to_int(Y) => from_int(Int) = Y)
:- typeclass enum(T) where [
    func to_int(T) = int,
    func from_int(int) = T is semidet
].

    % `det_from_int(I)' returns the result of `from_int(I)', but throws an
    % exception if `from_int' fails.
    %
:- func det_from_int(int) = T <= enum(T).

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