Basic Reversal Code w/ User Input

(define (reversal str)
  (if (= (string-length str) 0)
      ""
      (string-append
       (reversal (substring str 1 (string-length str)))
       (string-ith str 0)
       )
      )
  )

; Takes the first letter of the user input, puts it to the end, and then flips itself backwards.