141 lines
3.4 KiB
Prolog
141 lines
3.4 KiB
Prolog
/**
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* @file pl/lists.yap
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* @author VITOR SANTOS COSTA <vsc@VITORs-MBP.lan>
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* @date Thu Nov 19 09:54:00 2015
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*
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* @addtogroup lists
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* @{
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*/
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:- system_module( '$_lists', [], []).
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:- set_prolog_flag(source, true). % 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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/** @pred memberchk(+ _Element_, + _Set_)
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As member/2, 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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*/
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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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/** @pred member(? _Element_, ? _Set_)
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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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*/
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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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%% @pred identical_member(?Element, ?Set) is nondet
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%
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% identical_member holds true when Set is a list, and Element is
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% exactly identical to one of the elements that occurs in it.
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lists:identical_member(X,[Y|M]) :-
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(
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X == Y
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;
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M \= [], lists:identical_member(X,M)
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).
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/** @pred append(? _List1_,? _List2_,? _List3_)
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Succeeds when _List3_ unifies with the concatenation of _List1_
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and _List2_. The predicate can be used with any instantiation
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pattern (even three variables).
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*/
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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_prolog_flag(source, true). % :- 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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/** @pred delete(+ _List_, ? _Element_, ? _Residue_)
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eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
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True when _List_ is a list, in which _Element_ may or may not
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occur, and _Residue_ is a copy of _List_ with all elements
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identical to _Element_ deleted.
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eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
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*/
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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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:- set_prolog_flag(source, false). % disable source.
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% length of a list.
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/** @pred length(? _L_,? _S_)
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Unify the well-defined list _L_ with its length. The procedure can
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be used to find the length of a pre-defined list, or to build a list
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of length _S_.
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*/
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prolog:length(L, M) :-
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'$skip_list'(L, M, M0, R),
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( var(R) -> '$$_length'(R, M, M0) ;
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R == []
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).
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%
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% in case A1 is unbound or a difference list, things get tricky
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%
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'$$_length'(R, M, M0) :-
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( var(M) -> '$$_length1'(R,M,M0)
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; M >= M0 -> '$$_length2'(R,M,M0) ).
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%
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% Size is unbound, generate lists
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%
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'$$_length1'([], M, M).
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'$$_length1'([_|L], O, N) :-
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M is N + 1,
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'$$_length1'(L, O, M).
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%
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% Size is bound, generate single list
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%
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'$$_length2'(NL, O, N) :-
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( N =:= O -> NL = [];
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M is N + 1, NL = [_|L], '$$_length2'(L, O, M) ).
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%% @}
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