Question

Write a Scheme procedure named ‘proc4’ which takes 2 procedures as arguments (w,x) [note that w and x can be expected to work correctly when given two numbers as arguments]
and returns a procedure which takes 2 numbers (y,z) as arguments and returns the
procedure (w or x) which results in the greatest number when applied to y and z
(i.e. in C++ pseudocode if ((y w z) > (y x z)) {return w; } else {return x;} )

So I started

(define proc4(lamdda ( w x) (lambda y z)…
Then I wanted to do the if part. Something like
(if (> (apply w ( y z)) (apply x( w z))) but I keep getting errors.

I’ve been trying to find help on internet but everything I’ve seen so far does not make sense to me.

Answer 1

You can invoke function objects directly, without using apply:

(define (proc4 f g)
  (lambda (x y)
    (if (> (f x y) (g x y))
        f
        g)))