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yap-6.3/pl/sort.yap

56 lines
1.3 KiB
Prolog

/*************************************************************************
* *
* YAP Prolog *
* *
* Yap Prolog was developed at NCCUP - Universidade do Porto *
* *
* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
* *
**************************************************************************
* *
* File: sort.pl *
* Last rev: *
* mods: *
* comments: sorting in Prolog *
* *
*************************************************************************/
/* The three sorting routines are all variations of merge-sort, done by
bisecting the list, sorting the nearly equal halves, and merging the
results. The half-lists aren't actually constructed, the number of
elements is counted instead (which is why 'length' is in this file).
*/
% length of a list.
length(L,M) :- var(M), !, '$$_length1'(L,0,M).
length(L,M) :- '$$_length2'(M,L).
'$$_length1'([], M, M).
'$$_length1'([_|L], N, O) :-
M is N + 1,
'$$_length1'(L, M, O).
'$$_length2'(N, L) :-
( N =:= 0
->
L = []
;
L = [_|L1],
N > 0,
N1 is N - 1,
'$$_length2'(N1, L1)
).
sort(L,O) :-
'$sort'(L,O).
msort(L,O) :-
'$msort'(L,O).
keysort(L,O) :-
'$keysort'(L,O).