find the minimum item in a list, using a key to extract a value to minimize

minimize.lisp

(defun minimize (list &key (pred #'<) (key #'identity))
  "returns values: the minimum value and if there was one"
  (if (null list)
      (values nil nil)
    (values (loop with min-e = (first list)
                  with min-v = (funcall key min-e)
                  initially (pop list)
                  for e in list 
                  for v = (funcall key e)
                  if (funcall pred v min-v) do (setf min-e e min-v v)
                  finally (return min-e))
            t)))


CL-USER 35 > (minimize '((5 . a) (3 . b) (1 . c) (9 . d)) :key #'car)
(1 . C)
T