CODEWITHSUNDEEP
prolog
codezoner
codezoner

Reputation: 1064

Prolog predicate with two lists

I'm newbie to prolog and trying to understand this prolog code.

next_truth_value([0|R],[1|R]).
next_truth_value([1|R],[0|S]) :- next_truth_value(R,S).

Through my research I found that predicate contains two lists. If I query this I get a answer like this...

?- next_truth_value([0,0], NEXT).
NEXT = [1,0]

Please someone explain this code, I'm totally helpless about understanding what this really meant. Thank You.

Upvotes: 0

Views: 151

Answers (1)

Snicksie
Snicksie

Reputation: 1997

This code is calculating the next binary number (reversed). If you have a binary number 00, the next binary number is 01 (which is represented as [1,0]). Your predicate will change a zero into a one, but if there is already a one (like in the binary number 01), it will have to look further in the list to find a zero to turn into a one. This code will by the way not work for the list [1,1], it will return false.

You could also use the same code to find the previous binary number. If you use the predicate like this: next_truth_value(Prev,[1,0])., you will get the result [0,0].

Upvotes: 2

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