/* Part of SWI-Prolog
Author: Jan Wielemaker
E-mail: J.Wielemaker@vu.nl
WWW: http://www.swi-prolog.org
Copyright (c) 2001-2020, University of Amsterdam
SWI-Prolog Solutions b.v.
All rights reserved.
Redistribution and use in source and binary forms, with or without
modification, are permitted provided that the following conditions
are met:
1. Redistributions of source code must retain the above copyright
notice, this list of conditions and the following disclaimer.
2. Redistributions in binary form must reproduce the above copyright
notice, this list of conditions and the following disclaimer in
the documentation and/or other materials provided with the
distribution.
THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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*/
:- module(occurs,
[ contains_term/2, % +SubTerm, +Term
contains_var/2, % +SubTerm, +Term
free_of_term/2, % +SubTerm, +Term
free_of_var/2, % +SubTerm, +Term
occurrences_of_term/3, % +SubTerm, +Term, ?Tally
occurrences_of_var/3, % +SubTerm, +Term, ?Tally
sub_term/2, % -SubTerm, +Term
sub_var/2, % -SubTerm, +Term (SWI extra)
sub_term_shared_variables/3 % +Sub, +Term, -Vars
]).
/** Finding and counting sub-terms
This is a SWI-Prolog implementation of the corresponding Quintus
library, based on the generalised arg/3 predicate of SWI-Prolog.
@see library(terms) provides similar predicates and is probably
more wide-spread than this library.
*/
%! contains_term(+Sub, +Term) is semidet.
%
% Succeeds if Sub is contained in Term (=, deterministically)
contains_term(X, X) :- !.
contains_term(X, Term) :-
compound(Term),
arg(_, Term, Arg),
contains_term(X, Arg),
!.
%! contains_var(+Sub, +Term) is semidet.
%
% Succeeds if Sub is contained in Term (==, deterministically)
contains_var(X0, X1) :-
X0 == X1,
!.
contains_var(X, Term) :-
compound(Term),
arg(_, Term, Arg),
contains_var(X, Arg),
!.
%! free_of_term(+Sub, +Term) is semidet.
%
% Succeeds of Sub does not unify to any subterm of Term
free_of_term(Sub, Term) :-
\+ contains_term(Sub, Term).
%! free_of_var(+Sub, +Term) is semidet.
%
% Succeeds of Sub is not equal (==) to any subterm of Term
free_of_var(Sub, Term) :-
\+ contains_var(Sub, Term).
%! occurrences_of_term(@SubTerm, @Term, ?Count) is det.
%
% Count the number of SubTerms in Term that _unify_ with SubTerm. As
% this predicate is implemented using backtracking, SubTerm and Term
% are not further instantiated. Possible constraints are enforced. For
% example, we can count the integers in Term using
%
% ?- freeze(S, integer(S)), occurrences_of_term(S, f(1,2,a), C).
% C = 2,
% freeze(S, integer(S)).
%
% @see occurrences_of_var/3 for an equality (==/2) based variant.
occurrences_of_term(Sub, Term, Count) :-
count(sub_term(Sub, Term), Count).
%! occurrences_of_var(@SubTerm, @Term, ?Count) is det.
%
% Count the number of SubTerms in Term that are _equal_ to SubTerm.
% Equality is tested using ==/2. Can be used to count the occurrences
% of a particular variable in Term.
%
% @see occurrences_of_term/3 for a unification (=/2) based variant.
occurrences_of_var(Sub, Term, Count) :-
count(sub_var(Sub, Term), Count).
%! sub_term(-Sub, +Term)
%
% Generates (on backtracking) all subterms of Term.
sub_term(X, X).
sub_term(X, Term) :-
compound(Term),
arg(_, Term, Arg),
sub_term(X, Arg).
%! sub_var(-Sub, +Term)
%
% Generates (on backtracking) all subterms (==) of Term.
sub_var(X0, X1) :-
X0 == X1.
sub_var(X, Term) :-
compound(Term),
arg(_, Term, Arg),
sub_var(X, Arg).
%! sub_term_shared_variables(+Sub, +Term, -Vars) is det.
%
% If Sub is a sub term of Term, Vars is bound to the list of variables
% in Sub that also appear outside Sub in Term. Note that if Sub
% appears twice in Term, its variables are all considered shared.
%
% An example use-case is refactoring a large clause body by
% introducing intermediate predicates. This predicate can be used to
% find the arguments that must be passed to the new predicate.
sub_term_shared_variables(Sub, Term, Vars) :-
term_replace_first(Term, Sub, true, Term2),
term_variables(Term2, AllVars),
term_variables(Sub, SubVars),
intersection_eq(SubVars, AllVars, Vars).
term_replace_first(TermIn, From, To, TermOut) :-
term_replace_(TermIn, From, To, TermOut, done(_)).
%term_replace(TermIn, From, To, TermOut) :-
% term_replace_(TermIn, From, To, TermOut, all).
%! term_replace_(+From, +To, +TermIn, -TermOut, +Done)
%
% Replace instances (==/2) of From inside TermIn by To.
term_replace_(TermIn, _From, _To, TermOut, done(Done)) :-
Done == true,
!,
TermOut = TermIn.
term_replace_(TermIn, From, To, TermOut, Done) :-
From == TermIn,
!,
TermOut = To,
( Done = done(Var)
-> Var = true
; true
).
term_replace_(TermIn, From, To, TermOut, Done) :-
compound(TermIn),
compound_name_arity(TermIn, Name, Arity),
Arity > 0,
!,
compound_name_arity(TermOut, Name, Arity),
term_replace_compound(1, Arity, TermIn, From, To, TermOut, Done).
term_replace_(Term, _, _, Term, _).
term_replace_compound(I, Arity, TermIn, From, To, TermOut, Done) :-
I =< Arity,
!,
arg(I, TermIn, A1),
arg(I, TermOut, A2),
term_replace_(A1, From, To, A2, Done),
I2 is I+1,
term_replace_compound(I2, Arity, TermIn, From, To, TermOut, Done).
term_replace_compound(_I, _Arity, _TermIn, _From, _To, _TermOut, _).
%! intersection_eq(+Small, +Big, -Shared) is det.
%
% Shared are the variables in Small that also appear in Big. The
% variables in Shared are in the same order as Small.
intersection_eq([], _, []).
intersection_eq([H|T0], L, List) :-
( member_eq(H, L)
-> List = [H|T],
intersection_eq(T0, L, T)
; intersection_eq(T0, L, List)
).
member_eq(E, [H|T]) :-
( E == H
-> true
; member_eq(E, T)
).
/*******************************
* UTIL *
*******************************/
%! count(:Goal, -Count)
%
% Count number of times Goal succeeds.
:- meta_predicate count(0,-).
count(Goal, Count) :-
State = count(0),
( Goal,
arg(1, State, N0),
N is N0 + 1,
nb_setarg(1, State, N),
fail
; arg(1, State, Count)
).