29 lines
507 B
Perl
29 lines
507 B
Perl
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% you may need to update the module directive that follows for
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% compatibility with your Prolog compiler module system
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:- module(module, [mod_length/2]).
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mod_length(List, Length) :-
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integer(Length) ->
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Length >= 0,
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mod_make_list(Length, List)
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;
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mod_length(List, 0, Length).
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mod_make_list(0, []):-
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!.
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mod_make_list(N, [_| Tail]):-
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M is N-1,
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mod_make_list(M, Tail).
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mod_length([], Length, Length).
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mod_length([_| Tail], Acc, Length) :-
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Acc2 is Acc + 1,
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mod_length(Tail, Acc2, Length).
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