How can I apply each element in a list to a function in scheme?

问题

The function applyToAll is suppose to take in a function and a List, then take the car of the list and apply each element to the fuction.

This is what I have worked out so far:

(define applyToAll(lambda (f L)
                (cond
                  ((null? L)       '())
                  (#t              (cons (L) (applyToAll f(car L))))
                  )))

I'm not sure what I am doing wrong. A fuction call would look like

(applyToAll  (lambda (n) (* n n))    '(1 2 3) )  

and it would return

(1 4 9)

Instead it returns: function call: expected a function after the open parenthesis, but received (list 1 2 3)

Any help as to why my code is not working?

Thanks

回答1:

It sounds like you are trying to implement 'map'.

The error you are getting is because you are calling a list as though it's a funtion. (L) () this means funtion call in scheme - scheme doc

You are making the same error here:

 (#t              (cons (L) (applyToAll f(car L))))

the right way to apply is:

(function arg0 arg1 ... argn)

You need to apply f to each element in the list. this should work:

(cons (f (car L)) (applyToAll f (cdr L))))

the first elemnet:

(car L)

the rest of the list:

(cdr L)

gl

来源：https://stackoverflow.com/questions/42840761/how-can-i-apply-each-element-in-a-list-to-a-function-in-scheme