Question

I’m trying to add, say, x to every element of a list.
For example:

(queue 3 '(1 2 3))

would give

((3 1) (3 2) (3 3))

The code below apparently does not do what I want.
Any hints please?

(defun queue(x y)
 (cond
  ((null y) nil)
  (t (cons x (queue x (rest y)))))) 

Answer 1

You’re prepending x to to the result of applying queue to the rest of y, without using y’s first element at all. So basically you’re throwing away all values of y and replacing them with x.

You want to do (cons (list x (first y)) (queue x (rest y)))))) instead.

You could of course just use map to do this, but I assume this is an exercise in recursion.