Question

THIS IS A PROLOG QUESTION:

Write a Prolog rule to repeat each element of the list TWO times. Hint: You should use recursion.

For example, repeat_elements([a,b,c], Result) should return Result as [a,a,b,b,c,c]
The result of repeating an empty list [] is an empty list [] so your base case should be the following:

repeat_elements([], []). % This is the base case

Once you complete your rule by adding recursion rule to the base case, you should test it by a query:

% Test Query:
?- repeat_elements([a,b,c], Result). % Result would be [a, a, b, b, c, c]

Write your complete Prolog rule including both the provided base case and the recursion rule in the following field.

Answer 1

PREDICATES IN PROLOG:

repeat_elements([], []). %base case for empty list
%recursive case for non-empty list
repeat_elements([X|Y1], [X, X|Y2]):- repeat_elements(Y1, Y2).

OUTPUT:

repeat_elements([a,b,c), Result) Result = [a, a, b, b, c, c]

Regards!