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pl:prolog:pllib:list_length_3 [2019/06/27 15:50] (aktualna)
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 +====== 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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