nconc (a standard function in Common Lisp) is a destructive function that works like append.

> (define lst '(a b c))
lst

> (nconc lst '(d e))
(a b c d e)

> lst
(a b c d e)

nconc can be implemented as follows:

(define (nconc x y)
  (define (nconc2 x y)
    (if (pair? (cdr x))
        (nconc2 (cdr x) y)
        (set-cdr! x y)))
  (if (pair? x)
      (begin (nconc2 x y) x)
      y) )

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