;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; root.ss
;;;   A scheme program that prompts for values and prints
;;;   their square roots.
;;; Author:  Samuel A. Rebelsky
;;; Version: 1.0
;;; Created: Tuesday, 26 September 2000
;;;

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Procedures

;;; interactive-square-root
;;;   Repeatedly prompts for a number and prints its square root
;;; Parameters: None
;;; Preconditions: None
;;; Postconditions: Has read values from input.  Prints output.
;;; Produces: Nothing
(define interactive-square-root
  (lambda ()
    (display "Enter a number (or quit to quit): ")
    (isr-helper (read))))

;;; isr-helper
;;;   Helper procedure for interactive-square-root
;;;   Checks the value entered and does something appropriate
;;; Parameters: The value entered
(define isr-helper
  (lambda (val)
    (if (not (number? val))
        (quit)
        (begin
          (display "The square root of ")
          (display val)
          (display " is ")
          (display (sqrt val))
          (newline)
          (interactive-square-root)))))

;;; quit
;;;   Display a goodbye message.  (Doesn't really quit.)
;;; Parameters: None
;;; Preconditions: None
;;; Postconditions: Has displayed text.
;;; Produces: Nothing
(define quit
  (lambda ()
     (display "Bye!")
     (newline)))

;;; print-root
;;;   Displays information about the square root of a value
;;; Parameters: A value
;;; Preconditions: The value is a number.  (NOT CHECKED!)
;;; Postconditions: Has displayed helpful text.
;;; Produces: Nothing
(define print-root
  (lambda (value)
    (display "The square root of ")
    (display value)
    (display " is ")
    (display (sqrt value))
    (newline)))

;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
;;; Run the program

(interactive-square-root)