Question

PROLOG: Write a prolog predicate that counts occurrences of 'x', 'y', or 'z' in a list. For example, count([x,[y,[a,2],[a,3]],[a,4]], 2) should return true. I only want to count occurrences of x,y,z not a. the base case is that any [a,int] list will have a count of 0. So any sublist with 'a' does not count. another example of what will return true is: count([x,[a,1],[a,5]], 1) The predicate must have the form count(X,Y) where X is the list structure passed and Y is the count.

Answer 1

Prolog : predicate that count occurnce of 'x','y' or 'z' in a list.
?- count_occurrences([X], Occ).
Occ = [X] where { X= 'x','y','z'}

Bagof: this is a built-in predicate.

Syntax: bagof(true,member(X,List),Xs)

?- bagof(true,member(X,[x,y,a,b,c,2]),Xs).
X = x,
Xs = [true, true, true] ;
X = y,
Xs = [true, true, true] ;
X = a,
Xs = [false] ;
X = b,
Xs = [false] ;
X = c,
Xs = [false] ;

X = 2,

Xs = [false] ;

there are two methods to check occurrence in the list.

1.occurnce method - check occurrence in the list and return the value

2. bagof method - return true if the element contains in the list otherwise return false.

if X={'x','y' or 'z'} in the list then return true otherwise return false.