CODEWITHSUNDEEP
schemeracket
gibarian
gibarian

Reputation: 145

Compose a list by repeating the elements of a list in Scheme

I know that 

                  (define (repe k n) (make-list k n))

compose a list where n appears k times but... How can I construct a similar sentence for which k is the first element and n the second of a previous list?

My

             (define (repe x) (make-list car(x) cdr(x)) list)

does not seem to work.

On the other hand, I want the second element of the list n not to be a number but a letter. How can it be done (since make-list seems to be defined just for numbers)?

Upvotes: 0

Views: 373

Answers (1)

molbdnilo
molbdnilo

Reputation: 66371

Functions are applied like this: (car x) and (cdr x), not like car(x) and cdr(x).

And (cdr x) is a list - the second element is (car (cdr x)), or (cadr x) for short.

Your description isn't entirely clear, but it seems like you're looking for

(define (repe xs) (make-list (car xs) (cadr xs)))

Examples:

> (repe (list 4 #\Z))
'(#\Z #\Z #\Z #\Z)
> (repe (list 3 "hello"))
'("hello" "hello" "hello")
> (repe '(2 (+ 1 1)))
'((+ 1 1) (+ 1 1))

Upvotes: 1

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