Counting Sublist Elements in Prolog

Posted by idea_ on Stack Overflow See other posts from Stack Overflow or by idea_
Published on 2009-09-06T05:38:49Z Indexed on 2010/05/22 23:30 UTC
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How can I count nested list elements in prolog?

I have the following predicates defined, which will count a nested list as one element:

length([ ], 0).
length([H|T],N) :- length(T,M), N  is  M+1.

Usage:

?- length([a,b,c],Out).
Out = 3

This works, but I would like to count nested elements as well i.e.

length([a,b,[c,d,e],f],Output).
?- length([a,b,[c,d,e],f],Output).

Output = 6

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