/*************************************************************************
* *
* YAP Prolog %W% %G%
* *
* Yap Prolog was developed at NCCUP - Universidade do Porto *
* *
* Copyright L.Damas, V.S.Costa and Universidade do Porto 1985-1997 *
* *
**************************************************************************
* *
* File: setof.pl *
* Last rev: *
* mods: *
* comments: set predicates *
* *
*************************************************************************/
/**
* @file setof.yap
* @author VITOR SANTOS COSTA <vsc@VITORs-MBP.lan>
* @date Thu Nov 19 10:45:32 2015
*
* @brief Setof and friends.
*
*
*/
:- system_module( '$_setof', [(^)/2,
all/3,
bagof/3,
findall/3,
findall/4,
setof/3], []).
/**
*
* @defgroup Sets Collecting Solutions to a Goal
* @ingroup builtins
* @{
*
*
* When there are several solutions to a goal, if the user wants to collect all
* the solutions he may be led to use the data base, because backtracking will
* forget previous solutions.
*
* YAP allows the programmer to choose from several system
* predicates instead of writing his own routines. findall/3 gives you
* the fastest, but crudest solution. The other built-in predicates
* post-process the result of the query in several different ways:
*
*/
:- use_system_module( '$_boot', ['$catch'/3]).
:- use_system_module( '$_errors', ['$do_error'/2]).
% this is used by the all predicate
:- op(50,xfx,same).
%% @pred ^/2
%
% The "existential quantifier" symbol is only significant to bagof
% and setof, which it stops binding the quantified variable.
% op(200, xfy, ^) is defined during bootstrap.
_^Goal :-
'$execute'(Goal).
/** @pred findall( _T_,+ _G_,- _L_) is iso
findall/3 is a simplified version of bagof which has an implicit
existential quantifier on every variable.
Unifies _L_ with a list that contains all the instantiations of the
term _T_ satisfying the goal _G_.
With the following program:
~~~~~
a(2,1).
a(1,1).
a(2,2).
~~~~~
the answer to the query
~~~~~
findall(X,a(X,Y),L).
~~~~~
would be:
~~~~~
X = _32
Y = _33
L = [2,1,2];
no
~~~~~
*/
findall(Template, Generator, Answers) :-
must_be_of_type( list_or_partial_list, Answers ),
'$findall'(Template, Generator, [], Answers).
% If some answers have already been found
/** @pred findall( ?Key, +Goal, +InitialSolutions, -Solutions )
Similar to findall/3, but appends all answers to list _L0_.
*/
findall(Template, Generator, Answers, SoFar) :-
must_be_of_type( list_or_partial_list, Answers ),
'$findall'(Template, Generator, SoFar, Answers).
% starts by calling the generator,
% and recording the answers
'$findall'(Template, Generator, SoFar, Answers) :-
nb:nb_queue(Ref),
(
'$execute'(Generator),
nb:nb_queue_enqueue(Ref, Template),
fail
;
nb:nb_queue_close(Ref, Answers, SoFar)
).
% findall_with_key is very similar to findall, but uses the SICStus
% algorithm to guarantee that variables will have the same names.
%
'$findall_with_common_vars'(Template, Generator, Answers) :-
nb:nb_queue(Ref),
(
'$execute'(Generator),
nb:nb_queue_enqueue(Ref, Template),
fail
;
nb:nb_queue_close(Ref, Answers, []),
'$collect_with_common_vars'(Answers, _)
).
'$collect_with_common_vars'([], _).
'$collect_with_common_vars'([Key-_|Answers], VarList) :-
'$variables_in_term'(Key, _, VarList),
'$collect_with_common_vars'(Answers, VarList).
% This is the setof predicate
/** @pred setof( _X_,+ _P_,- _B_) is iso
Similar to `bagof( _T_, _G_, _L_)` but sorts list
_L_ and keeping only one copy of each element. Again, assuming the
same clauses as in the examples above, the reply to the query
~~~
setof(X,a(X,Y),L).
~~~
would be:
~~~
X = _32
Y = 1
L = [1,2];
X = _32
Y = 2
L = [2];
no
~~~
*/
setof(Template, Generator, Set) :-
( '$is_list_or_partial_list'(Set) ->
true
;
'$do_error'(type_error(list,Set), setof(Template, Generator, Set))
),
'$bagof'(Template, Generator, Bag),
'$sort'(Bag, Set).
% And this is bagof
% Either we have excess of variables
% and we need to find the solutions for each instantiation
% of these variables
/** @pred bagof( _T_,+ _G_,- _L_) is iso
For each set of possible instances of the free variables occurring in
_G_ but not in _T_, generates the list _L_ of the instances of
_T_ satisfying _G_. Again, assuming the same clauses as in the
examples above, the reply to the query
~~~
bagof(X,a(X,Y),L).
would be:
X = _32
Y = 1
L = [2,1];
X = _32
Y = 2
L = [2];
no
~~~
*/
bagof(Template, Generator, Bag) :-
( '$is_list_or_partial_list'(Bag) ->
true
;
'$do_error'(type_error(list,Bag), bagof(Template, Generator, Bag))
),
'$bagof'(Template, Generator, Bag).
'$bagof'(Template, Generator, Bag) :-
'$free_variables_in_term'(Template^Generator, StrippedGenerator, Key),
%format('TemplateV=~w v=~w ~w~n',[TemplateV,Key, StrippedGenerator]),
( Key \== '$' ->
'$findall_with_common_vars'(Key-Template, StrippedGenerator, Bags0),
'$keysort'(Bags0, Bags),
'$pick'(Bags, Key, Bag)
;
'$findall'(Template, StrippedGenerator, [], Bag0),
Bag0 \== [],
Bag = Bag0
).
% picks a solution attending to the free variables
'$pick'([K-X|Bags], Key, Bag) :-
'$parade'(Bags, K, Bag1, Bags1),
'$decide'(Bags1, [X|Bag1], K, Key, Bag).
'$parade'([K-X|L1], Key, [X|B], L) :- K == Key, !,
'$parade'(L1, Key, B, L).
'$parade'(L, _, [], L).
%
% The first argument to decide gives if solutions still left;
% The second gives the solution currently found;
% The third gives the free variables that are supposed to be bound;
% The fourth gives the free variables being currently used.
% The fifth outputs the current solution.
%
'$decide'([], Bag, Key0, Key, Bag) :- !,
Key0=Key.
'$decide'(_, Bag, Key, Key, Bag).
'$decide'(Bags, _, _, Key, Bag) :-
'$pick'(Bags, Key, Bag).
% as an alternative to setof you can use the predicate all(Term,Goal,Solutions)
% But this version of all does not allow for repeated answers
% if you want them use findall
/** @pred all( _T_,+ _G_,- _L_)
Similar to `findall( _T_, _G_, _L_)` but eliminate
repeated elements. Thus, assuming the same clauses as in the above
example, the reply to the query
~~~
all(X,a(X,Y),L).
~~~
would be:
~~~
X = _32
Y = _33
L = [2,1];
no
~~~
Note that all/3 will fail if no answers are found.
*/
all(T, G same X,S) :- !, all(T same X,G,Sx), '$$produce'(Sx,S,X).
all(T,G,S) :-
'$init_db_queue'(Ref),
( catch(G, Error,'$clean_findall'(Ref,Error) ),
'$execute'(G),
'$db_enqueue'(Ref, T),
fail
;
'$$set'(S,Ref)
).
% $$set does its best to preserve space
'$$set'(S,R) :-
'$$build'(S0,_,R),
S0 = [_|_],
S = S0.
'$$build'(Ns,S0,R) :- '$db_dequeue'(R,X), !,
'$$build2'(Ns,S0,R,X).
'$$build'([],_,_).
'$$build2'([X|Ns],Hash,R,X) :-
'$$new'(Hash,X), !,
'$$build'(Ns,Hash,R).
'$$build2'(Ns,Hash,R,_) :-
'$$build'(Ns,Hash,R).
'$$new'(V,El) :- var(V), !, V = n(_,El,_).
'$$new'(n(R,El0,L),El) :-
compare(C,El0,El),
'$$new'(C,R,L,El).
'$$new'(=,_,_,_) :- !, fail.
'$$new'(<,R,_,El) :- '$$new'(R,El).
'$$new'(>,_,L,El) :- '$$new'(L,El).
'$$produce'([T1 same X1|Tn],S,X) :- '$$split'(Tn,T1,X1,S1,S2),
( S=[T1|S1], X=X1;
!, produce(S2,S,X) ).
'$$split'([],_,_,[],[]).
'$$split'([T same X|Tn],T,X,S1,S2) :- '$$split'(Tn,T,X,S1,S2).
'$$split'([T1 same X|Tn],T,X,[T1|S1],S2) :- '$$split'(Tn,T,X,S1,S2).
'$$split'([T1|Tn],T,X,S1,[T1|S2]) :- '$$split'(Tn,T,X,S1,S2).
/**
@}
*/