I have been given a question in my assignment that asks to write a Prolog program that takes as input a list of numbers and succeeds if the list
contains only 0s.
I am having trouble on how to make the program search for zeroes. For example, a query like:
?- zero([0,0,0,0]).
Should give us true and it should return false whenever there's a number other than zero in it.
why are you asking us to do your homework for you? anyway, it's very simple recursion. something like:
zero([]).
zero([0|T]) :- zero(T).
just keep peeling of zero's until your list is empty. it isn't so hard ;)
Usually, one would not define a proper predicate for this, but rather use maplist/2 for the purpose:
..., maplist(=(0), Zs), ...
To give a concrete example:
?- Zs =[A,B,C], maplist(=(0), Zs).
This query corresponds to:
?- Zs = [A,B,C], call(=(0), A), call(=(0), B), call(=(0), C).
or even simpler:
?- Zs = [A,B,C], 0 = A, 0 = B, 0 = C.
If you want to define this as a separate predicate, remember to use a good name for it. Each element of the list is a zero, and the relation describes the entire list of such zeros. The convention for lists in this case is to use the plural word. Thus zeros/1:
zeros([]).
zeros([0|Zs]) :-
zeros(Zs).
