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recursionschemeracketconsr5rs

Scheme List Manipulation (Recursion)

The basic problem here is, when given a list, to return all elements of that list other than the last element. For example, given (a b c d) --> return (a b c). I essentially have the function, it's just the Scheme syntax that I'm having trouble with and Google isn't being very friendly. I'm not sure if I'm using cons correctly.

(define all-but-last
  (lambda (x)

   (if (null? (cdr x)) 
      ('()))
   (cons ((car x) (all-but-last(cdr x)))
)))

Someone who's knowledgeable with r5rs scheme syntax would be helpful. Thanks!

Solution

  • Using DrRacket with Language R5RS, this works:

    (define all-but-last
  (lambda (x)
   (if (null? x)
     '()
     (if (null? (cdr x)) 
       '()
       (cons (car x) (all-but-last(cdr x)))))))