a tail-recursion version list appending function

Question

i see several examples of implementing append an element to a list, but all are not using tail recursion. how to implement such a function in a

Answer 1

This is a functional, tail recursive append-elt using continuations:

(define (cont-append-elt lst elt)
  (let cont-loop ((lst lst)
                  (cont values))
    (if (null? lst)
        (cont (cons elt '()))
        (cont-loop (cdr lst)
                   (lambda (x) (cont (cons (car lst) x)))))))

Performance-wise it's close to Will's mutating one in Racket and Gambit but in Ikarus and Chicken Óscar's reverse did better. Mutation was always the best performer though. I wouldn't have used this however, but a slight version of Óscar's entry, purely because it is easier to read.

(define (reverse-append-elt lst elt)
  (reverse (cons elt (reverse lst))))

And if you want mutating performance I would have done:

(define (reverse!-append-elt lst elt)
  (let ((lst (cons elt (reverse lst))))
     (reverse! lst)
     lst))