(scheme) can define a function but can't call it

Question

I am trying to write a function that calls the map function N times on a list. Its a pretty simple problem:

(define (mapNtimes f x L)
  (if (= x 0)
        L
        (mapNtimes (f (- x 1) map (f L)))))

Dr Racket is gives me the following error when I try and call my function. Using a statement like this:

(mapNtimes ((lambda (x) (* 2 x))) 2 '(1 2 3))

It gives me this error

    expected: number?
    given: '(3 5 1)
    argument position: 2nd
    other arguments...:
    2

I know it something to do with the syntax but I can't for the life of me figure out what it is. Would appreciate some help.

Answer 1

Perhaps you are new to Scheme and not familiar with the syntax for invoking Scheme functions.

Given a function f, you invoke it using:

(f arg1 arg2)

not

f (arg1 arg2)

This works for me.

(define (mapNtimes f x L)
  (if (= x 0) L
    (mapNtimes f (- x 1) (map f L))))