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 semidet. 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) is semidet. 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) is semidet. 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) is det. 97% 98% Count the number of SubTerms in Term that _unify_ with SubTerm. As 99% this predicate is implemented using backtracking, SubTerm and Term 100% are not further instantiated. Possible constraints are enforced. For 101% example, we can count the integers in Term using 102% 103% ?- freeze(S, integer(S)), occurrences_of_term(S, f(1,2,a), C). 104% C = 2, 105% freeze(S, integer(S)). 106% 107% @see occurrences_of_var/3 for an equality (==/2) based variant. 108 109occurrences_of_term(Sub, Term, Count) :- 110 count(sub_term(Sub, Term), Count). 111 112%! occurrences_of_var(@SubTerm, @Term, ?Count) is det. 113% 114% Count the number of SubTerms in Term that are _equal_ to SubTerm. 115% Equality is tested using ==/2. Can be used to count the occurrences 116% of a particular variable in Term. 117% 118% @see occurrences_of_term/3 for a unification (=/2) based variant. 119 120occurrences_of_var(Sub, Term, Count) :- 121 count(sub_var(Sub, Term), Count). 122 123%! sub_term(-Sub, +Term) 124% 125% Generates (on backtracking) all subterms of Term. 126 127sub_term(X, X). 128sub_term(X, Term) :- 129 compound(Term), 130 arg(_, Term, Arg), 131 sub_term(X, Arg). 132 133%! sub_var(-Sub, +Term) 134% 135% Generates (on backtracking) all subterms (==) of Term. 136 137sub_var(X0, X1) :- 138 X0 == X1. 139sub_var(X, Term) :- 140 compound(Term), 141 arg(_, Term, Arg), 142 sub_var(X, Arg). 143 144 145%! sub_term_shared_variables(+Sub, +Term, -Vars) is det. 146% 147% If Sub is a sub term of Term, Vars is bound to the list of variables 148% in Sub that also appear outside Sub in Term. Note that if Sub 149% appears twice in Term, its variables are all considered shared. 150% 151% An example use-case is refactoring a large clause body by 152% introducing intermediate predicates. This predicate can be used to 153% find the arguments that must be passed to the new predicate. 154 (Sub, Term, Vars) :- 156 term_replace_first(Term, Sub, true, Term2), 157 term_variables(Term2, AllVars), 158 term_variables(Sub, SubVars), 159 intersection_eq(SubVars, AllVars, Vars). 160 161term_replace_first(TermIn, From, To, TermOut) :- 162 term_replace_(TermIn, From, To, TermOut, done(_)). 163 164%term_replace(TermIn, From, To, TermOut) :- 165% term_replace_(TermIn, From, To, TermOut, all). 166 167%! term_replace_(+From, +To, +TermIn, -TermOut, +Done) 168% 169% Replace instances (==/2) of From inside TermIn by To. 170 171term_replace_(TermIn, _From, _To, TermOut, done(Done)) :- 172 Done == true, 173 !, 174 TermOut = TermIn. 175term_replace_(TermIn, From, To, TermOut, Done) :- 176 From == TermIn, 177 !, 178 TermOut = To, 179 ( Done = done(Var) 180 -> Var = true 181 ; true 182 ). 183term_replace_(TermIn, From, To, TermOut, Done) :- 184 compound(TermIn), 185 compound_name_arity(TermIn, Name, Arity), 186 Arity > 0, 187 !, 188 compound_name_arity(TermOut, Name, Arity), 189 term_replace_compound(1, Arity, TermIn, From, To, TermOut, Done). 190term_replace_(Term, _, _, Term, _). 191 192term_replace_compound(I, Arity, TermIn, From, To, TermOut, Done) :- 193 I =< Arity, 194 !, 195 arg(I, TermIn, A1), 196 arg(I, TermOut, A2), 197 term_replace_(A1, From, To, A2, Done), 198 I2 is I+1, 199 term_replace_compound(I2, Arity, TermIn, From, To, TermOut, Done). 200term_replace_compound(_I, _Arity, _TermIn, _From, _To, _TermOut, _). 201 202%! intersection_eq(+Small, +Big, -Shared) is det. 203% 204% Shared are the variables in Small that also appear in Big. The 205% variables in Shared are in the same order as Small. 206 207intersection_eq([], _, []). 208intersection_eq([H|T0], L, List) :- 209 ( member_eq(H, L) 210 -> List = [H|T], 211 intersection_eq(T0, L, T) 212 ; intersection_eq(T0, L, List) 213 ). 214 215member_eq(E, [H|T]) :- 216 ( E == H 217 -> true 218 ; member_eq(E, T) 219 ). 220 221 222 /******************************* 223 * UTIL * 224 *******************************/ 225 226%! count(:Goal, -Count) 227% 228% Count number of times Goal succeeds. 229 230:- meta_predicate count(,). 231 232count(Goal, Count) :- 233 State = count(0), 234 ( , 235 arg(1, State, N0), 236 N is N0 + 1, 237 nb_setarg(1, State, N), 238 fail 239 ; arg(1, State, Count) 240 )