43 lines
1.2 KiB
Prolog
43 lines
1.2 KiB
Prolog
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:- system_module( '$_lists', [], []).
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:- '$set_yap_flags'(11,1). % source.
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% memberchk(+Element, +Set)
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% means the same thing, but may only be used to test whether a known
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% Element occurs in a known Set. In return for this limited use, it
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% is more efficient when it is applicable.
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lists:memberchk(X,[X|_]) :- !.
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lists:memberchk(X,[_|L]) :-
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lists:memberchk(X,L).
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% member(?Element, ?Set)
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% is true when Set is a list, and Element occurs in it. It may be used
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% to test for an element or to enumerate all the elements by backtracking.
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% Indeed, it may be used to generate the Set!
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lists:member(X,[X|_]).
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lists:member(X,[_|L]) :-
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lists:member(X,L).
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lists:append([], L, L).
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lists:append([H|T], L, [H|R]) :-
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lists:append(T, L, R).
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:- '$set_yap_flags'(11,0). % :- no_source.
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% lists:delete(List, Elem, Residue)
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% is true when List is a list, in which Elem may or may not occur, and
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% Residue is a copy of List with all elements identical to Elem lists:deleted.
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lists:delete([], _, []).
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lists:delete([Head|List], Elem, Residue) :-
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Head == Elem, !,
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lists:delete(List, Elem, Residue).
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lists:delete([Head|List], Elem, [Head|Residue]) :-
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lists:delete(List, Elem, Residue).
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