--- pl:prolog:pllib:list_length_3 [2019/06/27 15:50]
+++ pl:prolog:pllib:list_length_3 [2019/06/27 15:50] (aktualna)
@@ Linia 1: / Linia 1: @@
+====== List length 3 ======
+{{tag>lists}}
+===== Description =====
+Determining the length of a list.
+**Source**:  The Art of Prolog
+===== Download =====
+Program source code: {{list_length_3.pl}}
+===== Listing =====
+<code prolog>
+/*
+   mylength(Xs,N) :- The list Xs has length N.
+*/
+   mylength(Xs,N) :- nonvar(Xs), length1(Xs,N).
+   mylength(Xs,N) :- var(Xs), nonvar(N), length2(Xs,N).
+/*
+   length1(Xs,N) :- N is the length of the list Xs.
+*/
+     length1([X|Xs],N) :- length1(Xs,N1), N is N1+1.
+     length1([],0).
+/*
+   length2(Xs,N) :- Xs is a list of length N.
+*/
+     length2([X|Xs],N) :- N > 0, N1 is N-1, length2(Xs,N1).
+     length2([],0).
+%  Program 10.2    A multipurpose length program
+</code>
+===== Comments =====

pl/prolog/pllib/list_length_3.txt · ostatnio zmienione: 2019/06/27 15:50 (edycja zewnętrzna)

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