Pad numbers to same length

pad-numbers-to-same-length.lisp

(defun pad(thing) 
  (concatenate 'string "0" thing))

(defun pad-if-length-not-same(thing length)
  (cond
    ((not 
      (= (length thing) length)) 
        (pad thing))
    (t thing)))

(defun pad-list(things length) 
  (mapcar 
    (lambda (thing) 
      (pad-if-length-not-same thing length)) 
    things))

(defun pad-to-length(things length accumulator) 
  (cond 
    (
      (not (= accumulator (1- length))) 
        (pad-to-length 
          (pad-list things length) length (1+ accumulator)))
      (t things)))

(defun sort-by-length(a b) (< (length a) (length b)))

(defun get-largest-length(things) 
  (length
      (car
        (last
          (sort things #'sort-by-length)))))

(defun main(things) 
  (pad-to-length 
    things 
    (get-largest-length things) 
    0))

(print 
    (main '("1" "19" "2" "3" "55" "4" "12" "100" "1000")))