CODEWITHSUNDEEP
schemelisp
Tom
Tom

Reputation: 117

Scheme passing null list as function paramater

I'm doing some basic lisp/scheme and I am running into the problem where I can't pass an empty list/null (it is my understanding they behave almost identically) into a function. For example:

(define (fxn L) 
  (if (null? L)
      ( '() ) 
      (cdr L)))

And I am getting

> (fxn '())
procedure application: expected procedure, given: () (no arguments)

> (fxn null)
procedure application: expected procedure, given: () (no arguments)

Any advice?

Upvotes: 1

Views: 461

Answers (1)

Edgar Lepe
Edgar Lepe

Reputation: 66

This is happening because you have parentheses around '() in your if statement. '() is a literal not a function, therefore you can't call it, i.e, surround it in parentheses.

Try:

(define (fxn L)
  (if (null? L)
      '()
      (cdr L)))

Upvotes: 2

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