/* 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, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. */ :- 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) ).