I am now attempting to do the following ch5 question in Realm of Racket:
Change the Guess My Number game so that it displays the number of guesses the
program takes to find the players number. Hint: you might need to change the
data used to represent the data used to represent the world's state.
So what I did was to extend the interval struct from:
(struct interval (small big)
to
(struct interval (small big guesses)
Then I changed smaller (and bigger) like this:
(define (smaller w)
(interval (interval-small w)
(max (interval-small w)
(sub1 (guess w)))))
to
(define (smaller w)
(interval (interval-small w)
(max (interval-small w)
(sub1 (guess w))) ((+ interval-guesses 1) w)))
But with these changes, when I run the program I get:
+: contract violation
expected: number?
given: #<procedure:interval-guesses>
argument position: 1st
other arguments...:
1
In the Racket debugger it is complaining at the line (+ interval-guesses 1)
But surely, (+ interval-guesses 1) when evaluated would return a number???
Why am I getting this error? and how would I fix it?
Here is my full code for the program:
#lang racket
(require 2htdp/universe 2htdp/image)
(struct interval (small big guesses) #:transparent)
(define TEXT-SIZE 10)
(define HEIGHT 150)
(define COLOR "red")
(define SIZE 72)
(define TEXT-X 3)
(define TEXT-UPPER-Y 10)
(define TEXT-LOWER-Y 135)
(define HELP-TEXT
(text "up arrow for larger numbers, down arrow for smaller ones"
TEXT-SIZE
"blue"))
(define HELP-TEXT2
(text "Press = when your number is guessed; q for quit."
TEXT-SIZE
"blue"))
(define WIDTH (+ (image-width HELP-TEXT2) 10))
(define MT-SC
(place-image/align
HELP-TEXT TEXT-X TEXT-UPPER-Y "left" "top"
(place-image/align
HELP-TEXT2 TEXT-X TEXT-LOWER-Y "left" "bottom"
(empty-scene WIDTH HEIGHT))))
(define (guess w)
(quotient (+ (interval-small w) (interval-big w)) 2))
(define (render w)
(overlay (text (number->string (guess w)) SIZE COLOR) MT-SC))
(define (smaller w)
(interval (interval-small w)
(max (interval-small w)
(sub1 (guess w))) ((+ interval-guesses 1) w)))
(define (bigger w)
(interval (min (interval-big w)
(add1 (guess w)))
(interval-big w) ((+ interval-guesses 1) w)))
(define (deal-with-guess w key)
(cond [(key=? key "up") (bigger w)]
[(key=? key "down") (smaller w)]
[(key=? key "q") (stop-with w)]
[(key=? key "=") (stop-with w)]
[else w]))
(define (single? w)
(= (interval-small w) (interval-big w)))
(define (start lower upper)
(big-bang (interval lower upper 0)
(on-key deal-with-guess)
(to-draw render)
(stop-when single? render)))
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