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    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)  2019-2020, VU University Amsterdam
    7                              CWI, 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:
   13
   14    1. Redistributions of source code must retain the above copyright
   15       notice, this list of conditions and the following disclaimer.
   16
   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
   20       distribution.
   21
   22    THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
   23    "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
   24    LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
   25    FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
   26    COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
   27    INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
   28    BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
   29    LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
   30    CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   31    LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
   32    ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
   33    POSSIBILITY OF SUCH DAMAGE.
   34*/
   35
   36:- module(prolog_code,
   37          [ comma_list/2,                       % (A,B) <-> [A,B]
   38            semicolon_list/2,                   % (A;B) <-> [A,B]
   39
   40            mkconj/3,                           % +A, +B, -Conjunction
   41            mkdisj/3,                           % +A, +B, -Disjunction
   42
   43            pi_head/2,                          % :PI, :Head
   44            head_name_arity/3,			% ?Goal, ?Name, ?Arity
   45
   46            most_general_goal/2,                % :Goal, -General
   47            extend_goal/3,                      % :Goal, +Extra, -GoalOut
   48
   49            predicate_label/2,                  % +PI, -Label
   50            predicate_sort_key/2,               % +PI, -Key
   51
   52            is_control_goal/1,                  % @Term
   53            is_predicate_indicator/1,           % @Term
   54
   55            body_term_calls/2                   % :BodyTerm, -Goal
   56          ]).   57:- autoload(library(error),[must_be/2, instantiation_error/1]).   58:- autoload(library(lists),[append/3]).   59
   60:- meta_predicate
   61    body_term_calls(:, -).   62
   63:- multifile
   64    user:prolog_predicate_name/2.

Utilities for reasoning about code

This library collects utilities to reason about terms commonly needed for reasoning about Prolog code. Note that many related facilities can be found in the core as well as other libraries:

*/

 comma_list(?CommaList, ?List)
 semicolon_list(?SemicolonList, ?List)
True if CommaList is a nested term over the ','/2 (';'/2) functor and List is a list expressing the elements of the conjunction. The predicate is deterministic if at least CommaList or List is sufficiently instantiated. If both are partial structures it enumerates ever growing conjunctions and lists. CommaList may be left or right associative on input. When generated, the CommaList is always right associative.

This predicate is typically used to reason about Prolog conjunctions (disjunctions) as many operations are easier on lists than on binary trees over some operator.

   95comma_list(CommaList, List) :-
   96    phrase(binlist(CommaList, ','), List).
   97semicolon_list(CommaList, List) :-
   98    phrase(binlist(CommaList, ';'), List).
   99
  100binlist(Term, Functor) -->
  101    { nonvar(Term) },
  102    !,
  103    (   { Term =.. [Functor,A,B] }
  104    ->  binlist(A, Functor),
  105        binlist(B, Functor)
  106    ;   [Term]
  107    ).
  108binlist(Term, Functor) -->
  109    [A],
  110    (   var_tail
  111    ->  (   { Term = A }
  112        ;   { Term =.. [Functor,A,B] },
  113            binlist(B,Functor)
  114        )
  115    ;   \+ [_]
  116    ->  {Term = A}
  117    ;   binlist(B,Functor),
  118        {Term =.. [Functor,A,B]}
  119    ).
  120
  121var_tail(H, H) :-
  122    var(H).
 mkconj(A, B, Conj) is det
 mkdisj(A, B, Disj) is det
Create a conjunction or disjunction from two terms. Reduces on true (mkconj/2) and false (mkdisj/2). Note that a false encountered in a conjunction does not cause the conjunction to be false, i.e. semantics under side effects are preserved.

The Prolog , and ; operators are of type xfy, i.e. right associative. These predicates preserve this grouping. For example,

?- mkconj((a,b), c, Conj)
Conj = (a,b,c)
  138mkconj(A,B,Conj) :-
  139    (   is_true(A)
  140    ->  Conj = B
  141    ;   is_true(B)
  142    ->  Conj = A
  143    ;   mkconj_(A,B,Conj)
  144    ).
  145
  146mkconj_((A,B), C, Conj) =>
  147    Conj = (A,C2),
  148    mkconj_(B,C,C2).
  149mkconj_(A, B, C) =>
  150    C = (A,B).
  151
  152mkdisj(A,B,Disj) :-
  153    (   is_false(A)
  154    ->  Disj = B
  155    ;   is_false(B)
  156    ->  Disj = A
  157    ;   mkdisj_(A,B,Disj)
  158    ).
  159
  160mkdisj_((A;B), C, Disj) =>
  161    Disj = (A;C2),
  162    mkdisj_(B, C, C2).
  163mkdisj_(A, B, C) =>
  164    C = (A;B).
  165
  166is_true(Goal) :- Goal == true.
  167is_false(Goal) :- (Goal == false -> true ; Goal == fail).
 is_predicate_indicator(@Term) is semidet
True when Term is a predicate indicator
  173is_predicate_indicator(Var) :-
  174    var(Var),
  175    !,
  176    instantiation_error(Var).
  177is_predicate_indicator(PI) :-
  178    strip_module(PI, M, PI1),
  179    atom(M),
  180    (   PI1 = (Name/Arity)
  181    ->  true
  182    ;   PI1 = (Name//Arity)
  183    ),
  184    atom(Name),
  185    integer(Arity),
  186    Arity >= 0.
 pi_head(?PredicateIndicator, ?Goal) is det
Translate between a PredicateIndicator and a Goal term. The terms may have a module qualification.
Errors
- type_error(predicate_indicator, PredicateIndicator)
  195pi_head(PI, Head) :-
  196    '$pi_head'(PI, Head).
 head_name_arity(?Goal, ?Name, ?Arity) is det
Similar to functor/3, but deals with SWI-Prolog's zero-argument callable terms and avoids creating a non-callable term if Name is not an atom and Arity is zero.
  204head_name_arity(Goal, Name, Arity) :-
  205    '$head_name_arity'(Goal, Name, Arity).
 most_general_goal(+Goal, -General) is det
General is the most general version of Goal. Goal can be qualified.
See also
- is_most_general_term/1.
  213most_general_goal(Goal, General) :-
  214    var(Goal),
  215    !,
  216    General = Goal.
  217most_general_goal(Goal, General) :-
  218    atom(Goal),
  219    !,
  220    General = Goal.
  221most_general_goal(M:Goal, M:General) :-
  222    !,
  223    most_general_goal(Goal, General).
  224most_general_goal(Compound, General) :-
  225    compound_name_arity(Compound, Name, Arity),
  226    compound_name_arity(General, Name, Arity).
 extend_goal(:Goal0, +Extra, -Goal) is det
Extend the possibly qualified Goal0 with additional arguments from Extra. If Goal0 is insufficiantly instantiated (i.e., a variable), a term call(Goal0, ...) is returned.
  235extend_goal(Goal0, Extra, Goal) :-
  236    var(Goal0),
  237    !,
  238    Goal =.. [call,Goal0|Extra].
  239extend_goal(M:Goal0, Extra, M:Goal) :-
  240    extend_goal(Goal0, Extra, Goal).
  241extend_goal(Atom, Extra, Goal) :-
  242    atom(Atom),
  243    !,
  244    Goal =.. [Atom|Extra].
  245extend_goal(Goal0, Extra, Goal) :-
  246    compound_name_arguments(Goal0, Name, Args0),
  247    append(Args0, Extra, Args),
  248    compound_name_arguments(Goal, Name, Args).
  249
  250
  251		 /*******************************
  252		 *            LABELS		*
  253		 *******************************/
 predicate_label(++PI, -Label) is det
Create a human-readable label for the given predicate indicator. This notably hides the module qualification from user and built-in predicates. This predicate is intended for reporting predicate information to the user, for example in the profiler.

First PI is converted to a head and the hook prolog_predicate_name/2 is tried.

  265predicate_label(PI, Label) :-
  266    must_be(ground, PI),
  267    pi_head(PI, Head),
  268    user:prolog_predicate_name(Head, Label),
  269    !.
  270predicate_label(M:Name/Arity, Label) :-
  271    !,
  272    (   hidden_module(M, Name/Arity)
  273    ->  atomic_list_concat([Name, /, Arity], Label)
  274    ;   atomic_list_concat([M, :, Name, /, Arity], Label)
  275    ).
  276predicate_label(M:Name//Arity, Label) :-
  277    !,
  278    (   hidden_module(M, Name//Arity)
  279    ->  atomic_list_concat([Name, //, Arity], Label)
  280    ;   atomic_list_concat([M, :, Name, //, Arity], Label)
  281    ).
  282predicate_label(Name/Arity, Label) :-
  283    !,
  284    atomic_list_concat([Name, /, Arity], Label).
  285predicate_label(Name//Arity, Label) :-
  286    !,
  287    atomic_list_concat([Name, //, Arity], Label).
  288
  289hidden_module(system, _).
  290hidden_module(user, _).
  291hidden_module(M, Name/Arity) :-
  292    functor(H, Name, Arity),
  293    predicate_property(system:H, imported_from(M)).
  294hidden_module(M, Name//DCGArity) :-
  295    Arity is DCGArity+1,
  296    functor(H, Name, Arity),
  297    predicate_property(system:H, imported_from(M)).
 predicate_sort_key(+PI, -Key) is det
Key is the (module-free) name of the predicate for sorting purposes.
  303predicate_sort_key(_:PI, Name) :-
  304    !,
  305    predicate_sort_key(PI, Name).
  306predicate_sort_key(Name/_Arity, Name).
  307predicate_sort_key(Name//_Arity, Name).
 is_control_goal(@Goal)
True if Goal is a compiled Prolog control structure. The difference between control structures and meta-predicates is rather unclear. The constructs below are recognised by the compiler and cannot be redefined. Note that (if->then;else) is recognised as ((if->then);else).
  317is_control_goal(Goal) :-
  318    var(Goal),
  319    !, fail.
  320is_control_goal((_,_)).
  321is_control_goal((_;_)).
  322is_control_goal((_->_)).
  323is_control_goal((_|_)).
  324is_control_goal((_*->_)).
  325is_control_goal(\+(_)).
 body_term_calls(:BodyTerm, -Goal) is nondet
True when BodyTerm calls Goal. This predicate looks into control structures as well as meta predicates based on predicate_property/2.

When a variable is called, this is normally returned in Goal. Currently if a variable is called with additional arguments, e.g., call(Var, a1), this call is reported as call(Var, a1).

  336body_term_calls(M:Body, Calls) :-
  337    body_term_calls(Body, M, M, Calls).
  338
  339body_term_calls(Var, M, C, Calls) :-
  340    var(Var),
  341    !,
  342    qualify(M, C, Var, Calls).
  343body_term_calls(M:Goal, _, C, Calls) :-
  344    !,
  345    body_term_calls(Goal, M, C, Calls).
  346body_term_calls(Goal, M, C, Calls) :-
  347    qualify(M, C, Goal, Calls).
  348body_term_calls((A,B), M, C, Calls) :-
  349    !,
  350    (   body_term_calls(A, M, C, Calls)
  351    ;   body_term_calls(B, M, C, Calls)
  352    ).
  353body_term_calls((A;B), M, C, Calls) :-
  354    !,
  355    (   body_term_calls(A, M, C, Calls)
  356    ;   body_term_calls(B, M, C, Calls)
  357    ).
  358body_term_calls((A->B), M, C, Calls) :-
  359    !,
  360    (   body_term_calls(A, M, C, Calls)
  361    ;   body_term_calls(B, M, C, Calls)
  362    ).
  363body_term_calls((A*->B), M, C, Calls) :-
  364    !,
  365    (   body_term_calls(A, M, C, Calls)
  366    ;   body_term_calls(B, M, C, Calls)
  367    ).
  368body_term_calls(\+ A, M, C, Calls) :-
  369    !,
  370    body_term_calls(A, M, C, Calls).
  371body_term_calls(Goal, M, C, Calls) :-
  372    predicate_property(M:Goal, meta_predicate(Spec)),
  373    \+ ( functor(Goal, call, _),
  374         arg(1, Goal, A1),
  375         strip_module(A1, _, P1),
  376         var(P1)
  377       ),
  378    !,
  379    arg(I, Spec, SArg),
  380    arg(I, Goal, GArg),
  381    meta_calls(SArg, GArg, Call0),
  382    body_term_calls(Call0, M, C, Calls).
  383
  384meta_calls(0, Goal, Goal) :-
  385    !.
  386meta_calls(I, Goal0, Goal) :-
  387    integer(I),
  388    !,
  389    length(Extra, I),
  390    extend_goal(Goal0, Extra, Goal).
  391meta_calls(//, Goal0, Goal) :-
  392    extend_goal(Goal0, [_,_], Goal).
  393meta_calls(^, Goal0, Goal) :-
  394    !,
  395    strip_existential(Goal0, Goal).
  396
  397strip_existential(Var, Var) :-
  398    var(Var),
  399    !.
  400strip_existential(_^In, Out) :-
  401    strip_existential(In, Out).
  402
  403qualify(M, C, Goal, Calls) :-
  404    M == C,
  405    !,
  406    Calls = Goal.
  407qualify(M, _, Goal, M:Goal)