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) 2001-2020, University of Amsterdam 7 SWI-Prolog Solutions b.v. 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(occurs, 37 [ contains_term/2, % +SubTerm, +Term 38 contains_var/2, % +SubTerm, +Term 39 free_of_term/2, % +SubTerm, +Term 40 free_of_var/2, % +SubTerm, +Term 41 occurrences_of_term/3, % +SubTerm, +Term, ?Tally 42 occurrences_of_var/3, % +SubTerm, +Term, ?Tally 43 sub_term/2, % -SubTerm, +Term 44 sub_var/2, % -SubTerm, +Term (SWI extra) 45 sub_term_shared_variables/3 % +Sub, +Term, -Vars 46 ]). 47 48/** <module> Finding and counting sub-terms 49 50This is a SWI-Prolog implementation of the corresponding Quintus 51library, based on the generalised arg/3 predicate of SWI-Prolog. 52 53@see library(terms) provides similar predicates and is probably 54 more wide-spread than this library. 55*/ 56 57%! contains_term(+Sub, +Term) is semidet. 58% 59% Succeeds if Sub is contained in Term (=, deterministically) 60 61contains_term(X, X) :- !. 62contains_term(X, Term) :- 63 compound(Term), 64 arg(_, Term, Arg), 65 contains_term(X, Arg), 66 !. 67 68 69%! contains_var(+Sub, +Term) is det. 70% 71% Succeeds if Sub is contained in Term (==, deterministically) 72 73contains_var(X0, X1) :- 74 X0 == X1, 75 !. 76contains_var(X, Term) :- 77 compound(Term), 78 arg(_, Term, Arg), 79 contains_var(X, Arg), 80 !. 81 82%! free_of_term(+Sub, +Term) 83% 84% Succeeds of Sub does not unify to any subterm of Term 85 86free_of_term(Sub, Term) :- 87 \+ contains_term(Sub, Term). 88 89%! free_of_var(+Sub, +Term) 90% 91% Succeeds of Sub is not equal (==) to any subterm of Term 92 93free_of_var(Sub, Term) :- 94 \+ contains_var(Sub, Term). 95 96%! occurrences_of_term(+SubTerm, +Term, ?Count) 97% 98% Count the number of SubTerms in Term 99 100occurrences_of_term(Sub, Term, Count) :- 101 count(sub_term(Sub, Term), Count). 102 103%! occurrences_of_var(+SubTerm, +Term, ?Count) 104% 105% Count the number of SubTerms in Term 106 107occurrences_of_var(Sub, Term, Count) :- 108 count(sub_var(Sub, Term), Count). 109 110%! sub_term(-Sub, +Term) 111% 112% Generates (on backtracking) all subterms of Term. 113 114sub_term(X, X). 115sub_term(X, Term) :- 116 compound(Term), 117 arg(_, Term, Arg), 118 sub_term(X, Arg). 119 120%! sub_var(-Sub, +Term) 121% 122% Generates (on backtracking) all subterms (==) of Term. 123 124sub_var(X0, X1) :- 125 X0 == X1. 126sub_var(X, Term) :- 127 compound(Term), 128 arg(_, Term, Arg), 129 sub_var(X, Arg). 130 131 132%! sub_term_shared_variables(+Sub, +Term, -Vars) is det. 133% 134% If Sub is a sub term of Term, Vars is bound to the list of variables 135% in Sub that also appear outside Sub in Term. Note that if Sub 136% appears twice in Term, its variables are all considered shared. 137% 138% An example use-case is refactoring a large clause body by 139% introducing intermediate predicates. This predicate can be used to 140% find the arguments that must be passed to the new predicate. 141 (Sub, Term, Vars) :- 143 term_replace_first(Term, Sub, true, Term2), 144 term_variables(Term2, AllVars), 145 term_variables(Sub, SubVars), 146 intersection_eq(SubVars, AllVars, Vars). 147 148term_replace_first(TermIn, From, To, TermOut) :- 149 term_replace_(TermIn, From, To, TermOut, done(_)). 150 151%term_replace(TermIn, From, To, TermOut) :- 152% term_replace_(TermIn, From, To, TermOut, all). 153 154%! term_replace_(+From, +To, +TermIn, -TermOut, +Done) 155% 156% Replace instances (==/2) of From inside TermIn by To. 157 158term_replace_(TermIn, _From, _To, TermOut, done(Done)) :- 159 Done == true, 160 !, 161 TermOut = TermIn. 162term_replace_(TermIn, From, To, TermOut, Done) :- 163 From == TermIn, 164 !, 165 TermOut = To, 166 ( Done = done(Var) 167 -> Var = true 168 ; true 169 ). 170term_replace_(TermIn, From, To, TermOut, Done) :- 171 compound(TermIn), 172 compound_name_arity(TermIn, Name, Arity), 173 Arity > 0, 174 !, 175 compound_name_arity(TermOut, Name, Arity), 176 term_replace_compound(1, Arity, TermIn, From, To, TermOut, Done). 177term_replace_(Term, _, _, Term, _). 178 179term_replace_compound(I, Arity, TermIn, From, To, TermOut, Done) :- 180 I =< Arity, 181 !, 182 arg(I, TermIn, A1), 183 arg(I, TermOut, A2), 184 term_replace_(A1, From, To, A2, Done), 185 I2 is I+1, 186 term_replace_compound(I2, Arity, TermIn, From, To, TermOut, Done). 187term_replace_compound(_I, _Arity, _TermIn, _From, _To, _TermOut, _). 188 189%! intersection_eq(+Small, +Big, -Shared) is det. 190% 191% Shared are the variables in Small that also appear in Big. The 192% variables in Shared are in the same order as Small. 193 194intersection_eq([], _, []). 195intersection_eq([H|T0], L, List) :- 196 ( member_eq(H, L) 197 -> List = [H|T], 198 intersection_eq(T0, L, T) 199 ; intersection_eq(T0, L, List) 200 ). 201 202member_eq(E, [H|T]) :- 203 ( E == H 204 -> true 205 ; member_eq(E, T) 206 ). 207 208 209 /******************************* 210 * UTIL * 211 *******************************/ 212 213%! count(:Goal, -Count) 214% 215% Count number of times Goal succeeds. 216 217:- meta_predicate count(,). 218 219count(Goal, Count) :- 220 State = count(0), 221 ( , 222 arg(1, State, N0), 223 N is N0 + 1, 224 nb_setarg(1, State, N), 225 fail 226 ; arg(1, State, Count) 227 )