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+====== Subterm substitution ======
+{{tag>terms}}
+===== Description =====
+A procedure for substituting a subterm of a term by another subterm.
+**Source**:  PROLOG programming for artificial intelligence, 3rd Edition, Harlow, 2001, ISBN 0-201-40375-7.
+===== Download =====
+Program source code: {{subterm_substitution.pl}}
+===== Listing =====
+<code prolog>
+%  Figure 7.3  A procedure for substituting a subterm of a term by another subterm.
+% substitute( Subterm, Term, Subterm1, Term1):
+%    if all occurrences of Subterm in Term are substituted
+%    with Subterm1 then we get Term1.
+% Case 1: Substitute whole term
+substitute( Term, Term, Term1, Term1)  :-  !.
+% Case 2: Nothing to substitute
+substitute( _, Term, _, Term)  :-
+   atomic(Term), !.
+% Case 3: Do substitution on arguments
+substitute( Sub, Term, Sub1, Term1)  :-
+   Term  =..  [F|Args],                        % Get arguments
+   substlist( Sub, Args, Sub1, Args1),         % Perform substitution on them
+   Term1  =..  [F|Args1].
+substlist( _, [], _, []).
+substlist( Sub, [Term|Terms], Sub1, [Term1|Terms1])  :-
+   substitute( Sub, Term, Sub1, Term1),
+   substlist( Sub, Terms, Sub1, Terms1).
+</code>
+===== Comments =====

pl/prolog/pllib/subterm_substitution.txt · ostatnio zmienione: 2019/06/27 15:50 (edycja zewnętrzna)

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