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yap-6.3/pl/bootlists.yap

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2016-02-29 03:28:50 +00:00
/**
* @file pl/lists.yap
* @author VITOR SANTOS COSTA <vsc@VITORs-MBP.lan>
* @date Thu Nov 19 09:54:00 2015
*
* @addtogroup lists
* @{
*/
:- system_module( '$_lists', [], []).
:- set_prolog_flag(source, true). % source.
% memberchk(+Element, +Set)
% means the same thing, but may only be used to test whether a known
% Element occurs in a known Set. In return for this limited use, it
% is more efficient when it is applicable.
/** @pred memberchk(+ _Element_, + _Set_)
As member/2, but may only be used to test whether a known
_Element_ occurs in a known Set. In return for this limited use, it
is more efficient when it is applicable.
*/
lists:memberchk(X,[X|_]) :- !.
lists:memberchk(X,[_|L]) :-
lists:memberchk(X,L).
%% member(?Element, ?Set)
% is true when Set is a list, and Element occurs in it. It may be used
% to test for an element or to enumerate all the elements by backtracking.
% Indeed, it may be used to generate the Set!
/** @pred member(? _Element_, ? _Set_)
True when _Set_ is a list, and _Element_ occurs in it. It may be used
to test for an element or to enumerate all the elements by backtracking.
*/
lists:member(X,[X|_]).
lists:member(X,[_|L]) :-
lists:member(X,L).
%% @pred identical_member(?Element, ?Set) is nondet
%
% identical_member holds true when Set is a list, and Element is
% exactly identical to one of the elements that occurs in it.
lists:identical_member(X,[Y|M]) :-
(
X == Y
;
M \= [], lists:identical_member(X,M)
).
/** @pred append(? _List1_,? _List2_,? _List3_)
Succeeds when _List3_ unifies with the concatenation of _List1_
and _List2_. The predicate can be used with any instantiation
pattern (even three variables).
*/
lists:append([], L, L).
lists:append([H|T], L, [H|R]) :-
lists:append(T, L, R).
:- set_prolog_flag(source, true). % :- no_source.
% lists:delete(List, Elem, Residue)
% is true when List is a list, in which Elem may or may not occur, and
% Residue is a copy of List with all elements identical to Elem lists:deleted.
/** @pred delete(+ _List_, ? _Element_, ? _Residue_)
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
True when _List_ is a list, in which _Element_ may or may not
occur, and _Residue_ is a copy of _List_ with all elements
identical to _Element_ deleted.
eeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeeee
*/
lists:delete([], _, []).
lists:delete([Head|List], Elem, Residue) :-
Head = Elem,
lists:delete(List, Elem, Residue).
lists:delete([Head|List], Elem, [Head|Residue]) :-
lists:delete(List, Elem, Residue).
:- set_prolog_flag(source, false). % disable source.
% length of a list.
/** @pred length(? _L_,? _S_)
Unify the well-defined list _L_ with its length. The procedure can
be used to find the length of a pre-defined list, or to build a list
of length _S_.
*/
prolog:length(L, M) :-
'$skip_list'(L, M, M0, R),
( var(R) -> '$$_length'(R, M, M0) ;
R == []
).
%
% in case A1 is unbound or a difference list, things get tricky
%
'$$_length'(R, M, M0) :-
( var(M) -> '$$_length1'(R,M,M0)
; M >= M0 -> '$$_length2'(R,M,M0) ).
%
% Size is unbound, generate lists
%
'$$_length1'([], M, M).
'$$_length1'([_|L], O, N) :-
M is N + 1,
'$$_length1'(L, O, M).
%
% Size is bound, generate single list
%
'$$_length2'(NL, O, N) :-
( N =:= O -> NL = [];
M is N + 1, NL = [_|L], '$$_length2'(L, O, M) ).
%% @}