Lisp list iteration

Question

I have a function that gets x(a value) and xs(a list) and removes all values that are bigger than x from the list. Well it doesn't work, can you tell me why?

(defun biggerElems(x xs) 
  (let ((xst))
    (dolist (elem xs)
      (if (> x elem)
          (setf xst (remove elem xs))))
    xst))

Answer 1

I think it's this line that's not right:

(setf xst (remove elem xs))))

The first argument to setf is the place, followed by the value. It looks like you have it backwards (and xst is either nil or uninitialized).

You might find it easier to do this:

(defun biggerElems (x xs)
  (remove-if (lambda (item) (> item x)) xs))

Answer 2

Most concise AFAIK:

(defun bigger-elements (x xs) (remove x xs :test #'<))

returning a fresh list, it removes all elements y from xs for which

(< y x)

or using the famous LOOP:

(defun bigger-elements-2 (x xs) 
  (loop for e in xs
        unless (< e x)
        collect e))