guile-examples/programs/guess-the-number/main.scm

(import
 (except (rnrs base) let-values)
 (only (guile)
       lambda* λ)
 (ice-9 textual-ports))


;; Probably could improve here, by using SRFI uniform random
;; integer generation, but this is a toy example.
(define max-guesses 10)
(define max-target 100)
(define target (random max-target))


;; Define read-line or use whatever your Scheme dialect
;; offers.
(define read-line
  (lambda* (#:optional (input-port (current-input-port)))
    (get-line input-port)))


(let loop ([guesses-made 0])
  ;; Output a prompt in whatever way your Scheme dialect
  ;; does it.
  (display
   (simple-format
    #f "Type a number between 0 and ~a: " max-target))
  (cond
   [(< guesses-made max-guesses)
    (let ([guess (string->number (read-line))])
      (display (simple-format #f "You guessed: ~a.\n" guess))
      (cond
       [(= guess target)
        (display (simple-format #f "You win!\n"))]
       [(< guess target)
        (display (simple-format #f "Too small! Try again!\n"))
        (loop (+ guesses-made 1))]
       [else
        (display (simple-format #f "Too big! Try again!\n"))
        (loop (+ guesses-made 1))]))]
   [else
    (display (simple-format #f "All out of guesses. You lose!\n"))]))