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samples/solutions/all_solutions.m:
samples/solutions/some_solutions.m:
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53 lines
1.5 KiB
Mathematica
53 lines
1.5 KiB
Mathematica
% An example program to illustrate the use of the `do_while'
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% predicate in Mercury. This program calls a nondeterministic
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% predicate hello/1, prints the first solution it finds, and
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% then asks the user if they want any more solutions;
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% if they do, it finds another solution, prompts the user again,
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% and so on. It stops when there are no more solutions or
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% when the user says no to the "More?" prompt.
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%
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% Note that in the standard "commutative" semantics, the order of
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% solutions is unspecified. If you want to force the order of
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% evaluation, then you would need to use the "strict sequential semantics"
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% (enabled by the `--strict-sequential' option to the Mercury compiler).
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% This source file is hereby placed in the public domain. -fjh (the author).
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:- module some_solutions.
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:- interface.
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:- import_module io.
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:- pred main(io::di, io::uo) is cc_multi.
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:- implementation.
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:- import_module bool.
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:- import_module char.
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:- import_module list.
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:- import_module solutions.
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main(!IO) :-
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do_while(hello, get_next, !IO),
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io.write_string("No (more) solutions\n", !IO).
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:- pred hello(string::out) is multi.
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hello("Hello, world\n").
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hello("Good day, world\n").
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hello("Greetings, world\n").
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:- pred get_next(string::in, bool::out, io::di, io::uo) is det.
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get_next(String, More, !IO) :-
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% print the first answer
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io.write_string(String, !IO),
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% see if the user wants more answers
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io.write_string("More? ", !IO),
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io.read_line(Line, !IO),
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( if Line = ok([FirstChar|_]),
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char.to_upper(FirstChar, 'Y')
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then More = yes
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else More = no
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).
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