CODEWITHSUNDEEP
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Asqan
Asqan

Reputation: 4489

Invoking function with variable length of arguments

I have a function that takes a list of arguments with variable length. And depend on its length, i have to invoke another function, but with different length of arguments. You see the function below:

  (define (set-contents . args)
   (define columns-length (length args))
        (cond
          ((= columns-length 1) 
           (send output-list set (empty-list rows-length) (get-nth-item columns-as-list 0)))
          ((= columns-length 2) 
           (send output-list set (empty-list rows-length) (get-nth-item columns-as-list 0) (get-nth-item columns-as-list 1)))
          ((= columns-length 3) 
           (send output-list set (empty-list rows-length) (get-nth-item columns-as-list 0) (get-nth-item columns-as-list 1) (get-nth-item columns-as-list 2)))
          ((= columns-length 4) 
           (send output-list set (empty-list rows-length) (get-nth-item columns-as-list 0) (get-nth-item columns-as-list 1) (get-nth-item columns-as-list 2) (get-nth-item columns-as-list 3)))

This cond clause can be still longer. It is working but absolutely no proper.

Is there a better way to fill up this function?

Upvotes: 2

Views: 320

Answers (2)

WorBlux
WorBlux

Reputation: 1413

Use apply?

(define (set-contents . args)
  (define columns-length (length args))
  (apply send (append (list output-list set '()) 
                      (take column-length columns-as-list))))

(define (take num lst)
  (cond ((< num 1) '())
        ((null? lst) (error "Cannot TAKE from the empty list")
        (else (cons (car lst) (take (- num 1) (cdr lst))))))

Sure beats being a human compiler

Upvotes: 0

C. K. Young
C. K. Young

Reputation: 223193

Well, a direct translation of the idea is as follows:

(define (set-contents . args)
  (send/apply output-list set (empty-list rows-length)
                              (for/list ((i (length args)))
                                (get-nth-item columns-as-list i))))

But, since you're not actually using the arguments other than getting the argument count, that seems pretty fishy. What are you trying to do?

Upvotes: 2

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