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)  2010-2018, 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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   14    1. Redistributions of source code must retain the above copyright
   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
   19       the documentation and/or other materials provided with the
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   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   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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   34*/
   35
   36:- module(rdfql_runtime,
   37          [ rdfql_carthesian/1,         % +Bags
   38
   39            rdfql_bind_null/1,          % +List
   40            rdfql_cond_bind_null/1,     % +List
   41            rdfql_triple_in/2,          % -Triple, +Triples
   42
   43                                        % SeRQL support
   44            serql_compare/3,            % +Comparison, +Left, +Right
   45            serql_eval/2,               % +Term, -Evaluated
   46            serql_member_statement/2,   % -Triple, +List
   47
   48                                        % SPAQRL support
   49            sparql_true/1,              % +Term
   50            sparql_eval/2,              % +Expression, -Result
   51            sparql_find/5,              % ?From, ?To, ?F, ?T, :Q
   52            sparql_minus/2,             % :Q1, :Q2
   53            sparql_group/1,             % :Query
   54            sparql_group/3,             % :Query, +OuterVars, +InnerVars
   55            sparql_subquery/3,          % +Proj, +Query, +Solutions
   56            sparql_service/5,           % +Silent, +URL, +Prefixes, +Vars, +QText
   57            sparql_update/1             % +Updates
   58          ]).   59:- use_module(library(nb_set)).   60:- use_module(library(debug)).   61:- use_module(serql_runtime).   62:- use_module(sparql_runtime).   63
   64:- meta_predicate
   65    rdfql_carthesian(:).

   78                 /*******************************
   79                 *      CARTHESIAN PRODUCT      *
   80                 *******************************/

 rdfql_carthesian(:Bags) is nondet

Bags is a list of independent goals. This predicate provides the variable bindings for the carthesian product of all solutions of each goal in Bags. For example:

?- rdfql_carthesian([ bag([X], between(1,2,X)),
                      bag([Y], between(1,2,Y))]).
X = 1, Y = 1 ;
X = 1, Y = 2 ;
X = 2, Y = 1 ;
X = 2, Y = 2 ;
false.

   98rdfql_carthesian(M:Bags) :-
   99    solve_bags(Bags, M, 1, Sets),
  100    (   debugging(carthesian_size)
  101    ->  solution_set_size(Sets, Size),
  102        debug(carthesian_size, 'Total size = ~D; NO select', [Size])
  103    ;   true
  104    ),
  105    (   debugging(carthesian_no_select)
  106    ->  true
  107    ;   carthesian_select(Sets)
  108    ).
  109
  110solve_bags([], _, _, []).
  111solve_bags([bag(Templ, Goal, _Branch, _Cost)|T0], M, N, [set(Templ,Set,Size)|T]) :-
  112    empty_nb_set(Set),
  113    (   M:Goal,
  114        add_nb_set(Templ, Set),
  115        fail
  116    ;   true
  117    ),
  118    size_nb_set(Set, Size),
  119    debug(carthesian_bags, 'Bag ~d: solution size = ~D', [N, Size]),
  120    Size > 0,
  121    N2 is N + 1,
  122    solve_bags(T0, M, N2, T).
  123
  124
  125carthesian_select([]).
  126carthesian_select([call(Goal)|T]) :-
  127    call(Goal),
  128    carthesian_select(T).
  129carthesian_select([set(Templ,Set,_)|T]) :-
  130    gen_nb_set(Set, Templ),
  131    carthesian_select(T).
  132
  133solution_set_size([], 0).
  134solution_set_size([set(_,_,Len)|T], Size) :-
  135    (   T == []
  136    ->  Size = Len
  137    ;   solution_set_size(T, Size0),
  138        Size is Len * Size0
  139    ).
  140
  141
  142                 /*******************************
  143                 *          NULL HANDLING       *
  144                 *******************************/

 rdfql_cond_bind_null(+List) is det

Bind variables in List to our NULL-representation, which is $null$.

  151rdfql_cond_bind_null([]).
  152rdfql_cond_bind_null([H|T]) :-
  153    (   var(H)
  154    ->  H = '$null$'
  155    ;   true
  156    ),
  157    rdfql_cond_bind_null(T).

 rdfql_bind_null(+List) is semidet

True if all elements in List unify with $null$.

  163rdfql_bind_null([]).
  164rdfql_bind_null(['$null$'|T]) :-
  165    rdfql_bind_null(T).

 rdfql_triple_in(-Triple, +Triples) is nondet

True when Triple is an rdf(S,P,O) element in Triples that does not contain NULL. Used for CONSTRUCT and DESCRIBE.

  173rdfql_triple_in(Triple, Triples) :-
  174    Triple = rdf(S,P,O),
  175    member(Triple, Triples),
  176    S \== '$null$',
  177    P \== '$null$',
  178    O \== '$null$'