Michael Price wrote:

> Of course, after going through all of that you then see why loop is so
> handy:
>
> CL-USER> (defun nth-elements (n &rest lists)
> (loop for item in lists collect (nth n item)))
>
> NTH-ELEMENTS
> CL-USER> (nth-elements 3 '(10 20 hello x world) '(-1 -2 -3 y) '(z0 z1 z2 z))
>
> (X Y Z)

Instead of CL, let's use a Lisp.

Gauche Scheme and Racket:

(define (nth-elements n . seqs)
(map (& list-ref u n) seqs))

(nth-elements 3
'(10 20 hello x world)
'(-1 -2 -3 y)
'(z0 z1 z2 z))

===>
(x y z)

Given:

(define-syntax &-aux
(syntax-rules (u v w & lambda quote)
[(_ () shadow (param ...) original)
(lambda (param ...) original)]
[(_ (u more ...) (x y ...) () original)
(&-aux original original (x) original)]
[(_ (v more ...) (x y ...) (a) original)
(&-aux original original (a x) original)]
[(_ (w more ...) (x y ...) (a b) original)
(&-aux () () (a b x) original)]
[(_ ((lambda x ...) more ...) (y z ...) params original)
(&-aux (more ...) (z ...) params original)]
[(_ ((& x ...) more ...) (y z ...) params original)
(&-aux (more ...) (z ...) params original)]
[(_ ((quote x ...) more ...) (y z ...) params original)
(&-aux (more ...) (z ...) params original)]
[(_ ('x more ...) (y z ...) params original)
(&-aux (more ...) (z ...) params original)]
[(_ ((s ...) more ...) (y z ...) params original)
(&-aux (s ... more ...) (s ... z ...) params original)]
[(_ (x more ...) (y z ...) params original)
(&-aux (more ...) (z ...) params original)]))
;; Lambda with anaphoric parameters u, v, and w.
(define-syntax &
(syntax-rules ()
[(& x ...)
(&-aux (x ...) (x ...) () (x ...))]))