Singly-linked list/Element removal: Difference between revisions

=={{header|Racket}}==

This is written entirely in terms of car and cdr (the linked list/pair primitives in Racket and Scheme). Usually, you'd have reverse and append available to you... but, again, it's interesting to see how they are implemented (by me, at least)

<lang racket>#lang racket/base

(define (rev l (acc null))

(if (null? l)

acc

(rev (cdr l) (cons (car l) acc))))

(define (++ l m)

(if (null? l)

m

(let recur ((l-rev (rev l)) (acc m))

(if (null? l-rev)

acc

(recur (cdr l-rev) (cons (car l-rev) acc))))))

(define (remove-at l i (acc null))

(cond

[(null? l) (rev acc)]

[(positive? i) (remove-at (cdr l) (sub1 i) (cons (car l) acc))]

[else (++ (rev acc) (cdr l))]))

(displayln (remove-at '(1 2 3) 0))

(displayln (remove-at '(1 2 3) 1))

(displayln (remove-at '(1 2 3) 2))

(displayln (remove-at '(1 2 3) 3))</lang>

{{out}}

<pre>(2 3)

(1 3)

(1 2)

(1 2 3)</pre>