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a12692a0de
Keep the old style comments where they do not go to the end of the line, or where it is important that the comment line not have a // on it.
62 lines
2.0 KiB
Mathematica
62 lines
2.0 KiB
Mathematica
%---------------------------------------------------------------------------%
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% vim: ft=mercury ts=4 sw=4 et
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%---------------------------------------------------------------------------%
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% Copyright (C) 2000, 2005-2006, 2011 The University of Melbourne.
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% Copyright (C) 2014-2016, 2018 The Mercury team.
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% This file is distributed under the terms specified in COPYING.LIB.
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%---------------------------------------------------------------------------%
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%
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% File: counter.m.
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% Author: zs.
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% Stability: high.
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%
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% Predicates for dealing with counters, which are mechanisms for allocating
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% consecutively numbered integers. The abstraction barrier eliminates the
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% possibility of confusion along the lines of "does this counter record
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% the next number to be handed out, or the last number that was handed out?".
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%
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%---------------------------------------------------------------------------%
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%---------------------------------------------------------------------------%
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:- module counter.
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:- interface.
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%---------------------------------------------------------------------------%
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:- type counter.
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% init(N, Counter) returns a counter whose first allocation will be the
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% integer N.
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%
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:- pred init(int::in, counter::out) is det.
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% A function version of init/2.
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%
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:- func init(int) = counter.
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% allocate(N, Counter0, Counter) takes a counter, and returns (a) the next
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% integer to be allocated from that counter, and (b) the updated state of
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% the counter.
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%
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:- pred allocate(int::out, counter::in, counter::out) is det.
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%---------------------------------------------------------------------------%
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%---------------------------------------------------------------------------%
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:- implementation.
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:- import_module int.
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:- type counter
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---> counter(int).
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init(N, counter.init(N)).
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init(N) = counter(N).
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allocate(N, counter(N), counter(N + 1)).
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%---------------------------------------------------------------------------%
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:- end_module counter.
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%---------------------------------------------------------------------------%
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