/usr/share/Yap/pairs.pl is in yap 5.1.3-6.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
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Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: wielemak@science.uva.nl
WWW: http://www.swi-prolog.org
Copyright (C): 1985-2006, University of Amsterdam
This program is free software; you can redistribute it and/or
modify it under the terms of the GNU General Public License
as published by the Free Software Foundation; either version 2
of the License, or (at your option) any later version.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public
License along with this library; if not, write to the Free Software
Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
As a special exception, if you link this library with other files,
compiled with a Free Software compiler, to produce an executable, this
library does not by itself cause the resulting executable to be covered
by the GNU General Public License. This exception does not however
invalidate any other reasons why the executable file might be covered by
the GNU General Public License.
*/
:- module(pairs,
[ pairs_keys_values/3,
pairs_values/2,
pairs_keys/2,
group_pairs_by_key/2,
transpose_pairs/2,
map_list_to_pairs/3
]).
/** <module> Operations on key-value lists
This module implements common operations on Key-Value lists, also known
as _Pairs_. Pairs have great practical value, especially due to
keysort/2 and the library assoc.pl.
This library is based on disussion in the SWI-Prolog mailinglist,
including specifications from Quintus and a library proposal by Richard
O'Keefe.
@see keysort/2, library(assoc)
@author Jan Wielemaker
*/
%% pairs_keys_values(?Pairs, ?Keys, ?Values) is det.
%
% True if Keys holds the keys of Pairs and Values the values.
%
% Deterministic if any argument is instantiated to a finite list
% and the others are either free or finite lists.
pairs_keys_values(Pairs, Keys, Values) :-
( nonvar(Pairs) ->
pairs_keys_values_(Pairs, Keys, Values)
; nonvar(Keys) ->
keys_values_pairs(Keys, Values, Pairs)
; values_keys_pairs(Values, Keys, Pairs)
).
pairs_keys_values_([], [], []).
pairs_keys_values_([K-V|Pairs], [K|Keys], [V|Values]) :-
pairs_keys_values_(Pairs, Keys, Values).
keys_values_pairs([], [], []).
keys_values_pairs([K|Ks], [V|Vs], [K-V|Pairs]) :-
keys_values_pairs(Ks, Vs, Pairs).
values_keys_pairs([], [], []).
values_keys_pairs([V|Vs], [K|Ks], [K-V|Pairs]) :-
values_keys_pairs(Vs, Ks, Pairs).
%% pairs_values(+Pairs, -Values) is det.
%
% Remove the keys from a list of Key-Value pairs. Same as
% pairs_keys_values(Pairs, _, Values)
pairs_values([], []).
pairs_values([_-V|T0], [V|T]) :-
pairs_values(T0, T).
%% pairs_keys(+Pairs, -Keys) is det.
%
% Remove the values from a list of Key-Value pairs. Same as
% pairs_keys_values(Pairs, Keys, _)
pairs_keys([], []).
pairs_keys([K-_|T0], [K|T]) :-
pairs_keys(T0, T).
%% group_pairs_by_key(+Pairs, -Joined:list(Key-Values)) is det.
%
% Group values with the same key. For example:
%
% ==
% ?- group_pairs_by_key([a-2, a-1, b-4], X).
%
% X = [a-[2,1], b-[4]]
% ==
%
% @param Pairs Key-Value list, sorted to the standard order
% of terms (as keysort/2 does)
% @param Joined List of Key-Group, where Group is the
% list of Values associated with Key.
group_pairs_by_key([], []).
group_pairs_by_key([M-N|T0], [M-[N|TN]|T]) :-
same_key(M, T0, TN, T1),
group_pairs_by_key(T1, T).
same_key(M, [M-N|T0], [N|TN], T) :- !,
same_key(M, T0, TN, T).
same_key(_, L, [], L).
%% transpose_pairs(+Pairs, -Transposed) is det.
%
% Swap Key-Value to Value-Key and sort the result on Value
% (the new key) using keysort/2.
transpose_pairs(Pairs, Transposed) :-
flip_pairs(Pairs, Flipped),
keysort(Flipped, Transposed).
flip_pairs([], []).
flip_pairs([Key-Val|Pairs], [Val-Key|Flipped]) :-
flip_pairs(Pairs, Flipped).
%% map_list_to_pairs(:Function, +List, -Keyed)
%
% Create a key-value list by mapping each element of List.
% For example, if we have a list of lists we can create a
% list of Length-List using
%
% ==
% map_list_to_pairs(length, ListOfLists, Pairs),
% ==
:- module_transparent
map_list_to_pairs/3,
map_list_to_pairs2/3.
map_list_to_pairs(Function, List, Pairs) :-
map_list_to_pairs2(List, Function, Pairs).
map_list_to_pairs2([], _, []).
map_list_to_pairs2([H|T0], Pred, [K-H|T]) :-
call(Pred, H, K),
map_list_to_pairs2(T0, Pred, T).
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