scheme define list as local variable

Question

My target is do define list as local variable in order to get max element from it. My code:

#lang racket
(define (f a b c)
    (list (+ (* a a) (* b b) (* c c)) (+ a c))
    (define (max-of-list-2 lst)
      (foldr max (first lst) (rest lst)))
  (max max_from_list 12))
(f 5 6 7)

In second row I have defined list with calculated falues. My target is to pass it to next row in order to get max number from it, and finaly to get max from max of list and 12. What I do wrong. How to handle it?

https://www.gnu.org/software/mit-scheme/documentation/mit-scheme-ref/Lexical-Binding.html — bipll, Apr 28 '19 at 13:30
name it with another define: `(define lst (list ...))`. then you can refer to it by name in any lisp expression, like e.g. a function call. — Will Ness, Apr 28 '19 at 13:53
@IntoTheDeep what about `(max (max-of-list-2 lst) 12)`? @IntoTheDeep — Will Ness, Apr 28 '19 at 14:30
@IntoTheDeep It's difficult for us to take your non-working code and work out your actual intentions. Can you please describe the problem better? Can you think of a better name than `f`? What is the return value supposed to be? What is the point of the `(* a a)` `(* b b)` `(* c c)` and `(+ a c)` values? Is this just an assignment? — Mulan, Apr 28 '19 at 15:30
For `(max max-of-list-2 (lst) 12)` to work `lst` cannot be a list, but a procedure. You'll get [application: not a procedure](https://stackoverflow.com/questions/48064955/my-code-signals-the-error-application-not-a-procedure-or-call-to-non-procedu) — Sylwester, Apr 28 '19 at 23:39

score 1 · Accepted Answer · answered Apr 29 '19 at 06:55

You can use several defines at the top of your function.

So you meant

(define (f a b c)
  (define lst (list (+ (* a a) (* b b) (* c c)) 
                    (+ a c)))
  (define (max-of-list-2 lst)
      (foldr max (first lst) (rest lst)))
  (max (max-of-list-2 lst) 12))

but that's just equivalent to

(define (f a b c)
  (foldr max 12 (list (+ (* a a) (* b b) (* c c)) 
                      (+ a c))))

score 0 · Answer 2 · answered Apr 28 '19 at 14:35

0

You need to use an inner define, like this:

(define (f a b c)
    (define max_from_list (list (+ (* a a) (* b b) (* c c)) (+ a c)))
    (define (max-of-list-2 lst)
      (foldr max (first lst) (rest lst)))
  (max max_from_list 12))

answered Apr 28 '19 at 14:35

river

1,028
6
16

score 0 · Answer 3 · answered Apr 28 '19 at 15:33

It's somewhat difficult to work out your intentions, but this is the best understanding I can come up with -

(define (max a b)
  (if (< a b)
      b
      a))

(define (f a . more)
  (if (empty? more)
      (max a 12)
      (max a (apply f more))))

(f 5 6 7)
; => 12

(f 5 20 30)
; => 30

scheme define list as local variable

3 Answers3