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Return multiple values: Difference between revisions
→addsub.m
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Mercury is a logic language. Its unification semantics permit any number of output parameters (the closest equivalent to return values). The sample code provided here centres on the <code>addsub/4</code> predicate. The <code>mode</code> statement identifies the first two parameters as input parameters and the last two as output parameters, thus, in effect, returning two results. In this case the first output parameter returns the sum of the two inputs and the second output returns the difference of the two inputs.
===addsub.m===
<lang mercury>
:- module addsub.
:- interface.
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main(!IO) :-
(
X =
Y =
addsub(X, Y, S, D),
;
).
:- pred addsub(int::in, int::in, int::out, int::out) is det.
addsub(X, Y, S, D) :-
S = X + Y,
D = X - Y.
</lang>
===Use and output===
<pre><nowiki>$ mmc addsub.m -E && ./addsub 100 999
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