CODEWITHSUNDEEP
listlispelement
Kobek
Kobek

Reputation: 1211

LISP How to remove element at certain index from a list

I'm trying to learn LISP. I got my way around functions and I wanted to test myself with some.

I was trying to write a function that can remove an element from a list in a given index.

This seems pretty straightforward, but I can't manage to do it.

Example: I have the list (20 8 13 10) and I want to remove the number at index 2.

How would I go about something like this?

Upvotes: 1

Views: 2518

Answers (1)

Sylwester
Sylwester

Reputation: 48745

It's very easy. This is the base case:

(remove-nth 0 '(2 3)) ; => (3)

And the default case:

(remove-nth 1 '(1 2 3))         ; ==
(cons 1 (remove-nth 0 '(2 3)))

The only thing left for you to do is to actually implement it!

There is a third case. What if the list is nil? In the strictest sense you cannot do the job and you should signal an error or perhaps there isn't anything to do so it's ok to then have it as a base case that evaluates to '() so that (remove-nth 5 '(1 2)) ; ==> (1 2)

Upvotes: 2

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