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:
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   15       notice, this list of conditions and the following disclaimer.
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   17    2. Redistributions in binary form must reproduce the above copyright
   18       notice, this list of conditions and the following disclaimer in
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   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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   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

 predsort(:Compare, +List, -Sorted) is det

Sorts similar to sort/2, but determines the order of two terms by calling Compare(-Delta, +E1, +E2). This call must unify Delta with one of <, > or =. If built-in predicate compare/3 is used, the result is the same as sort/2 (but sort/2 is built using more low-level primitives and is considerably faster).

See also

- keysort/2 provides an more portable way to sort on arbitrary keys that is usually faster.

   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).

 locale_sort(+List, -Sorted) is det

Sort a list of atoms using the current locale.

Arguments:

List	- List of atoms
Sorted	- Sorted atoms.

  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)