(define (american-time h m s)
  (cond ((< h 0)
           (laml-error "Cannot handle this hour:" h))

        ((and (= h 12) (= m 0) (= s 0))
             "noon")

        ((< h 12)
           (string-append
             (format-hour-minutes-seconds h m s) 
             " " "am"))

        ((= h 12)  
           (string-append
             (format-hour-minutes-seconds h m s) 
             " " "pm"))

        ((and (= h 24) (= m 0) (= s 0))
             "midnight")

        ((<= h 24)
           (string-append 
             (format-hour-minutes-seconds (- h 12) m s) 
             " " "pm"))

        (else
           (laml-error "Cannot handle this hour:" h))))


(define (format-hour-minutes-seconds h m s)
 (string-append
  (zero-pad-string (number->string  h)) ":"
  (zero-pad-string (number->string  m)) ":"
  (zero-pad-string (number->string  s))))


(define (zero-pad-string str)
 (if (= 1 (string-length str))
     (string-append "0" str)
     str))