% generated: 16 November 1989
% option(s): SOURCE_TRANSFORM_1
%
%   qsort
%
%   David H. D. Warren
%   Copyright: Public domain
%
%   quicksort a list of 50 integers

top:-qsort.

qsort :- qsort([27,74,17,33,94,18,46,83,65, 2,
		32,53,28,85,99,47,28,82, 6,11,
		55,29,39,81,90,37,10, 0,66,51,
		 7,21,85,27,31,63,75, 4,95,99,
		11,28,61,74,18,92,40,53,59, 8],_,[]).

qsort([X|L],R,R0) :-
	partition(L,X,L1,L2),
	qsort(L2,R1,R0),
	qsort(L1,R,[X|R1]).
qsort([],R,R).

partition([X|L],Y,[X|L1],L2) :-
	X =< Y, !,
	partition(L,Y,L1,L2).
partition([X|L],Y,L1,[X|L2]) :-
	partition(L,Y,L1,L2).
partition([],_,[],[]).