#lang racket
(require "utilities.rkt")

;; ------------------------------------------------------------------------
;; the set-up: a simple program
;; ------------------------------------------------------------------------

(define hypotenuse
  (lambda (m n)
    (sqrt (+ (* m m) (* n n)))))

(define right-triangle
  (lambda ()
    (let ((x (read-num "One side of triangle:"))
          (y (read-num "The other side:")))
      (displayln "The hypotenuse is "
                 (hypotenuse x y)))))

;; ------------------------------------------------------------------------
;; read-num
;; ------------------------------------------------------------------------

(define read-num
  (lambda (prompt)
    (display prompt)
    (display " ")
    (let ((answer (read)))
      (if (number? answer)
          answer
          (begin (displayln "Illegal value")
                 (read-num prompt))))))

;; ------------------------------------------------------------------------
;; read-type produces prompted read functions for any given type!
;; Notice how it uses letrec to create and return a recursive function.
;; ------------------------------------------------------------------------

(define read-type
  (lambda (type?)
    (letrec ((reader (lambda (prompt)
                       (display prompt)
                       (display " ")
                       (let ((answer (read)))
                         (if (type? answer)
                             answer
                             (begin (displayln "Illegal value")
                                    (reader prompt)))))))
      reader)))

;; (define read-num (read-type number?))
;; (define read-str (read-type string?))

;; ------------------------------------------------------------------------