1/*  Part of SWI-Prolog
    2
    3    Author:        Jan Wielemaker
    4    E-mail:        J.Wielemaker@vu.nl
    5    WWW:           http://www.swi-prolog.org
    6    Copyright (c)  2006-2012, University of Amsterdam
    7                              Vu University Amsterdam
    8    All rights reserved.
    9
   10    Redistribution and use in source and binary forms, with or without
   11    modification, are permitted provided that the following conditions
   12    are met:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
   19       the documentation and/or other materials provided with the
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36:- module(sort,
   37          [ predsort/3,                 % :Compare, +List, -Sorted
   38            locale_sort/2               % +ListOfAtoms, -Sorted
   39          ]).   40
   41:- set_prolog_flag(generate_debug_info, false).   42
   43:- meta_predicate
   44    predsort(3, +, -).              % 3: Delta, Left, Right
   45
   46%!  predsort(:Compare, +List, -Sorted) is det.
   47%
   48%   Sorts similar to sort/2, but determines   the order of two terms
   49%   by calling Compare(-Delta, +E1, +E2). This call must unify Delta
   50%   with one of <, > or =.  If built-in predicate compare/3 is used,
   51%   the result is the same as sort/2 (but sort/2 is built using more
   52%   low-level primitives and is considerably faster).
   53%
   54%   @see keysort/2 provides an more portable way to sort on
   55%   arbitrary keys that is usually faster.
   56
   57predsort(P, L, R) :-
   58    '$skip_list'(N, L, Tail),
   59    (   Tail == []
   60    ->  predsort(P, N, L, _, R1),
   61        R = R1
   62    ;   must_be(L, list)
   63    ).
   64
   65predsort(P, 2, [X1, X2|L], L, R) :-
   66    !,
   67    call(P, Delta, X1, X2),
   68    sort2(Delta, X1, X2, R).
   69predsort(_, 1, [X|L], L, [X]) :- !.
   70predsort(_, 0, L, L, []) :- !.
   71predsort(P, N, L1, L3, R) :-
   72    N1 is N // 2,
   73    plus(N1, N2, N),
   74    predsort(P, N1, L1, L2, R1),
   75    predsort(P, N2, L2, L3, R2),
   76    predmerge(P, R1, R2, R).
   77
   78sort2(<, X1, X2, [X1, X2]).
   79sort2(=, X1, _,  [X1]).
   80sort2(>, X1, X2, [X2, X1]).
   81
   82predmerge(_, [], R, R) :- !.
   83predmerge(_, R, [], R) :- !.
   84predmerge(P, [H1|T1], [H2|T2], Result) :-
   85    call(P, Delta, H1, H2),
   86    !,
   87    predmerge(Delta, P, H1, H2, T1, T2, Result).
   88
   89predmerge(>, P, H1, H2, T1, T2, [H2|R]) :-
   90    predmerge(P, [H1|T1], T2, R).
   91predmerge(=, P, H1, _, T1, T2, [H1|R]) :-
   92    predmerge(P, T1, T2, R).
   93predmerge(<, P, H1, H2, T1, T2, [H1|R]) :-
   94    predmerge(P, T1, [H2|T2], R).
   95
   96%!  locale_sort(+List, -Sorted) is det.
   97%
   98%   Sort a list of atoms using the current locale.
   99%
  100%   @param List     List of atoms
  101%   @param Sorted   Sorted atoms.
  102
  103locale_sort(List, Sorted) :-
  104    collation_keys(List, Keyed),
  105    keysort(Keyed, KeySorted),
  106    unkey(KeySorted, Sorted).
  107
  108collation_keys([], []).
  109collation_keys([H|T0], [K-H|T]) :-
  110    collation_key(H, K),
  111    collation_keys(T0, T).
  112
  113
  114unkey([], []).
  115unkey([_-H|T0], [H|T]) :-
  116    unkey(T0, T)