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)  2006-2023, University of Amsterdam
    7                              VU University Amsterdam
    8                              SWI-Prolog Solutions b.v.
    9    All rights reserved.
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   36
   37:- module(sort,
   38          [ predsort/3,                 % :Compare, +List, -Sorted
   39            locale_sort/2               % +ListOfAtoms, -Sorted
   40          ]).   41
   42:- set_prolog_flag(generate_debug_info, false).   43
   44:- meta_predicate
   45    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 a more portable way to sort on arbitrary keys that is usually faster. The predicate sort/4 can sort on specific arguments of compound terms or key values of dicts.

   60predsort(P, L, R) :-
   61    '$skip_list'(N, L, Tail),
   62    (   Tail == []
   63    ->  predsort(P, N, L, _, R1),
   64        R = R1
   65    ;   must_be(L, list)
   66    ).
   67
   68predsort(P, 2, [X1, X2|L], L, R) :-
   69    !,
   70    call(P, Delta, X1, X2),
   71    sort2(Delta, X1, X2, R).
   72predsort(_, 1, [X|L], L, [X]) :- !.
   73predsort(_, 0, L, L, []) :- !.
   74predsort(P, N, L1, L3, R) :-
   75    N1 is N // 2,
   76    plus(N1, N2, N),
   77    predsort(P, N1, L1, L2, R1),
   78    predsort(P, N2, L2, L3, R2),
   79    predmerge(P, R1, R2, R).
   80
   81sort2(<, X1, X2, [X1, X2]).
   82sort2(=, X1, _,  [X1]).
   83sort2(>, X1, X2, [X2, X1]).
   84
   85predmerge(_, [], R, R) :- !.
   86predmerge(_, R, [], R) :- !.
   87predmerge(P, [H1|T1], [H2|T2], Result) :-
   88    call(P, Delta, H1, H2),
   89    !,
   90    predmerge(Delta, P, H1, H2, T1, T2, Result).
   91
   92predmerge(>, P, H1, H2, T1, T2, [H2|R]) :-
   93    predmerge(P, [H1|T1], T2, R).
   94predmerge(=, P, H1, _, T1, T2, [H1|R]) :-
   95    predmerge(P, T1, T2, R).
   96predmerge(<, P, H1, H2, T1, T2, [H1|R]) :-
   97    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.

  106locale_sort(List, Sorted) :-
  107    collation_keys(List, Keyed),
  108    keysort(Keyed, KeySorted),
  109    unkey(KeySorted, Sorted).
  110
  111collation_keys([], []).
  112collation_keys([H|T0], [K-H|T]) :-
  113    collation_key(H, K),
  114    collation_keys(T0, T).
  115
  116
  117unkey([], []).
  118unkey([_-H|T0], [H|T]) :-
  119    unkey(T0, T)