CODEWITHSUNDEEP
scheme
Skoolpsych2008
Skoolpsych2008

Reputation: 23

What am I doing wrong with Scheme?

When I enter the following:

(define (root a b c)
   (/ (+ (-b) (sqrt (- (exp b 2) (* 4 a c)))) (* 2 a)))

and then enter:

(root 3 6 2)

I get a message indicating that the procedure had two arguments but only requires exactly one. What am I doing wrong?

Upvotes: 2

Views: 755

Answers (3)

Óscar López
Óscar López

Reputation: 236004

The procedure exp raises the number e to the power of its argument, if you need to raise an argument to the power of another argument, use expt. Even better, given that you only need to square b, a simple multiplication will do. Like this:

(define (root a b c)
   (/ (+ (- b) (sqrt (- (* b b) (* 4 a c))))
      (* 2 a)))

Upvotes: 1

Joel J. Adamson
Joel J. Adamson

Reputation: 723

The function the error refers to is exp which takes only one argument. The exp function calculates the exponential function, not an exponent. You want expt, which raises a root x to the exponent y:

(expt b 2)

You can also just multiply the number times itself.

I usually keep R5RS or The Scheme Programming Language on hand since these basic functions can be hard to keep straight.

Upvotes: 1

Paige Ruten
Paige Ruten

Reputation: 176665

The exp function doesn't do exponents really, it does something else mathy. (I don't know.)

What you want is usually called pow for "power" but probably isn't defined in your environment, so I suggest you just define your own square method:

(define (square x) (* x x))

And then:

(define (root a b c)
   (/ (+ (- b) (sqrt (- (square b) (* 4 a c)))) (* 2 a)))

Edit: Oh, you'll also have to change a couple spacing issues, like (* 4 a c) instead of (*4 a c), and (- b) instead of (-b). You always have to separate the operator from the operands with spaces.

Upvotes: 4

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