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75 lines
2.2 KiB
Mathematica
75 lines
2.2 KiB
Mathematica
% This source file is hereby placed in the public domain. -fjh (the author).
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%-----------------------------------------------------------------------------%
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:- module mercury_lib.
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:- interface.
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:- import_module io.
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% To avoid link errors, there still has to be a main/2 defined somewhere
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% in the program; it won't be used, unless the C program calls
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% mercury_call_main(), which will call main/2.
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:- pred main(io__state::di, io__state::uo) is det.
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% a Mercury predicate with multiple modes
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:- pred foo(int).
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:- mode foo(in) is semidet.
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:- mode foo(out) is multi.
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% a Mercury function with multiple modes
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:- func bar(int) = int.
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:- mode bar(in) = out is det.
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:- mode bar(out) = in is det.
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:- mode bar(in) = in is semidet.
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% a semidet (i.e. partial) Mercury function
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:- func baz(int) = int.
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:- mode baz(in) = out is semidet.
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%-----------------------------------------------------------------------------%
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:- implementation.
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:- import_module std_util, int, list.
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% for this example, main/2 isn't useful
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main --> [].
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% well, this is just a silly example...
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foo(42).
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foo(53).
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foo(197).
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bar(X) = X + 1.
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baz(1) = 9.
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baz(2) = 16.
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baz(3) = 27.
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%-----------------------------------------------------------------------------%
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% The following code provides provides access to the Mercury predicate foo
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% from C code.
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:- pragma export(foo(in), "foo_test").
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:- pragma export(bar(in) = out, "bar").
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:- pragma export(bar(in) = in, "bar_test").
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:- pragma export(bar(out) = in, "bar_inverse").
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:- pragma export(baz(in) = out, "baz").
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% The nondet mode of `foo' cannot be exported directly with
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% the current Mercury/C interface. To get all solutions,
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% must define a predicate which returns all the solutions of foo,
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% and export it to C. We give it the name foo_list() in C.
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:- pred all_foos(list(int)::out) is det.
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:- pragma export(all_foos(out), "foo_list").
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all_foos(L) :- solutions((pred(X::out) is multi :- foo(X)), L).
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% If we just want one solution, and don't care which one, then
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% we can export a `cc_multi' (committed-choice nondeterminism)
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% version of `foo'. We give it the name one_foo().
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:- pred cc_foo(int::out) is cc_multi.
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:- pragma export(cc_foo(out), "one_foo").
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cc_foo(X) :- foo(X).
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%-----------------------------------------------------------------------------%
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