在球拍中实现全部应用功能

Question

I am trying to write a function apply-all that is passed a list of functions and a number, and produces a list of the values of the functions when applied to that number

For example,

(apply-all (list sqrt square cube) 4) => (2 16 64))

assuming that all functions have been previously defined

I know how to write each function separately and how that would work but I am a little confused about how to go about doing this one and processing what functions are passed

Answer 1

You need to traverse the function list and, for each function in turn, apply it to the number parameter. The easiest way to do this is by using the map procedure:

(define (apply-all flist num)
  (map (lambda (f) (f num))
       flist))

(apply-all (list sqrt square cube) 4)
=> '(2 16 64)

Answer 2

Here's a way to do it that I like, using for/list :

(define (apply-all fs n)
  (for/list ([f fs])
     (f n)))

Answer 3

(define (apply-all fs n)
  (cond
    ((null? fs) fs)
     (else (cons ((car fs) n) (apply-all ??? ???)))))

Is probably what you were supposed to write, if this was an assignment.