Scheme pass variables to a variadic function

Question

I have the following variadic function (define doSomething (lambda (x . rest) .... The function is called by using numbers, for example: (doSomething 1 2 3 4 5) (so with that call x would be 1 and rest would be (2 3 4 5)).

When I try to recursively call the function and put the second number (2) as x and rest as (3 4 5) I somehow receive the rest parameter as a list of list: ((3 4 5)).

This is how I currently try to call the function again: (+ x (doSomething (car rest) (cdr rest)))

It is worth mentioning that I'm using Pretty Big. Please advise, thanks.

hexist · Accepted Answer · 2012-10-30 13:28:02Z

2

So you're mix and matching what rest is, in your first call

(doSomething 1 2 3 4 5)   ; x = 1  rest = '(2 3 4 5)

In your subsequent calls you'll end up with

(doSomething (car rest) (cdr rest))   ; x=2  rest = '((3 4 5))

because rest is a variadic argument, so it takes everything after the first argument and makes it a list called rest for you, hence the double-listing. You'll probably want to be using apply or something, ie something like:

(define doSomething (lambda (x . rest) 
                      (display x) 
                      (if (not (null? rest))
                        (apply doSomething rest)
                        #f)))

answered Oct 30, 2012 at 13:28

hexist

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