Manipulating a Schema List (Recursion)

Question

The main problem is that when setting the list, return all the elements of this list that are different from the last element. For example, given (abcd) -> return (abc). I have a function, it's just the syntax of the circuit I'm having problems with, and Google is not very friendly. I'm not sure if I use the cons correctly.

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

Someone who is well versed in r5rs syntax will be helpful. Thanks!

Answer 1

Using DrRacket with the R5RS language, this works:

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

Answer 2

If you remove the extra parentheses around '() and the cons arguments, the code will work (for non-empty input lists).

Answer 3

Alternative solution:

 (define (all-but-last xs) (reverse (rest (reverse xs)))) 

Answer 4

See the answers to this question:

deletion of the last element of the list (scheme)

Also, I'm going to mark this as "homework." If it is not, let me know and I will delete it.

Answer 5

if you pass '() to your function, I think you should specify an error message other than return' ()