SICP Exercise 1.40 Issue

Question

Hi I am trying to solution SICP 1.40

I am using DrRacket and I keep getting this error:

define: expected only one expression for the function body, but found 2 extra parts

on this area of the code

This is my full code:

  (* x x))

(define (cube x) (* x x x))

(define (cubic a b c)
  (lambda (x)
    (+ (cube x)
       (* a (square x))
       (* b x) c)))

; Newton's methods pages 97 to 102
(define (deriv g)
    (lambda (x) (/ (- (g (+ x dx)) (g x)) dx)))
(define dx 0.00001)
(define tolerance 0.00001)
(define (fixed-point f first-guess)
    (define (close-enough? v1 v2)
        (< (abs (- v1 v2)) tolerance))
    (define (try guess)
        (let ((next (f guess)))
            (if (close-enough? guess next)
                next
                (try next))))
    (try first-guess))
(define (newton-transform g)
    (lambda (x) (- x (/ (g x) ((deriv g) x)))))

(define (newtons-method g guess) (fixed-point (newton-transform g) guess))

Please let me know what are your thoughs. I am new to both tool and loanguage. Thank you!

Answer 1

You're using one of the teaching languages that come with Racket, it looks like this one has some restrictions: for example, you cannot have more than one expression inside a procedure definition.

This is easy to fix, just switch to a more powerful language. Click on the bottom-left corner of Racket's window, and select "Determine language from source". Edit your source file so it starts with a line specifying the language you want to use:

#lang racket

Now you'll have full access to all the language features, both for beginners and advanced users. Alternatively, you could use a language tailored for SICP, this is highly recommended:

#lang sicp