Member Avatar for lotrsimp12345

how would you do that?

Language similar to LISP

I don't think you can use cons twice.

really stuck.

maybe
(define a '('()))

Edited by lotrsimp12345 because: n/a
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  • Latest Post Latest Post by davibq

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A list of lists in Scheme can be a literal or built at runtime. As correctly pointed out, a single-quote before a list literal produces a constant list structure; alternatively, use list or cons to construct one in code. The concern from about using cons repeatedly is unnecessary — you can nest cons calls — but ensure the second argument you cons onto is a proper list (otherwise you get an improper/dotted pair).

Example using list (clear and idiomatic):

(define a (list (list) (list) (list)))

Example helper to produce N empty lists programmatically:

(define (n-empty-lists n)
  (if (zero? n)
      (list)
      (cons (list) (n-empty-lists (- n 1)))))

General notes and cautions: prefer list for readability and to create fresh lists rather than relying on quoted literals when you plan to mutate data. Mutating literal structures with set-car! or set-cdr! is unspecified and should be avoided. If you see a dotted pair printed, check that the cdr you passed to cons was actually a list, not some other value.

Member Avatar for davibq

Like this: '(() () ()) -> 3 lists inside 1
(define a '(()))
You only have to put 1 quote..

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