Drracket: Finding highest value in a list without in built function

Question

This assignment for a class I'm in has me pretty confused. I was able to get most of the function working but this one part is what's keeping me from completing it. I have two functions which is what I need one is to find the highest number value in a list (largest-num) and the other situates the list and is what refers to it (max-lon). I get the following error largest-num: expects only 1 argument, but found 2 and im not quite sure how to fix it. Code is listed:

(define (max-lon a-lon)
  (local [
          (define ACUMM (void))
          (define lst   (void))
          ;; lon number → number
          ;; Purpose: Return max(max of given list, given number)
          ;; Accumulator Invariant: accum = maximum in L - lst
          (define (max-helper)
            (if(empty? lst)
                ACUMM
                (begin
                  (set! ACUMM (largest-num (first lst) ACUMM))
                  (set! lst (rest lst)) 
                  (max-helper))))]
     
    (if (empty? a-lon)
        (error 'max-lon "An empty lon does not have a maximum.")

        (begin
          (set! ACUMM(first a-lon))
          (set! lst (rest a-lon))
          (max-helper)))))

(define (largest-num lst)
  (cond 
    [(empty? (rest lst)) (first lst)]
    [(< (first lst) (first (rest lst))) (largest-num (rest lst))] 
    [else (largest-num (cons (first lst) (rest (rest lst))))]))  

Any suggestions would be great, thank you

Answer 1

largest-num can be simplified a lot more since all it has to do is compare two numbers which is ACUMM which is the accumulator/place in the list and first lst is what holds the highest number rather than processing the whole list which I assumed at first, here is fixed code:

(define (max-lon a-lon)
  (local [
          (define ACUMM (void))
          (define lst   (void))

          (define (max-helper)
            (if(empty? lst)
                ACUMM
                (begin
                  (set! ACUMM (largest? ACUMM (first lst))) 
                  (set! lst (rest lst)) 
                  (max-helper))))]
     
    (if (empty? a-lon)
        (error 'max-lon "An empty lon does not have a maximum.") 
        
        (begin
          (set! ACUMM(first a-lon))
          (set! lst (rest a-lon))
          (max-helper))))) 

(define (largest? a b)
  (if (> a b) a b))

Answer 2

(define (largest-num lst (acc -inf.0))
  (cond ((empty? lst) acc)
        ((and acc (> (car lst) acc)) (largest-num (cdr lst) (car lst)))
        (else (largest-num (cdr lst) acc))))