Jussi Piitulainen scripsit:

> Not sure what there is already but I donate the following.

Thanks.  I rewrote this using letrec* as:

(define (means ton)
  (letrec*
     ((mean
        (lambda (f g)
          (f (/ (sum g ton) n))))
      (sum
        (lambda (g ton)
          (if (null? ton)
            (+)
            (if (number? ton)
                (g ton)
                (+ (sum g (car ton))
                   (sum g (cdr ton)))))))
      (n (sum (lambda (x) 1) ton)))
    (values (mean values values)
            (mean exp log)
            (mean / /))))

and added your example to both the errata page and the errata branch.

See LetrecStar on the wiki for which Schemes implement letrec*,
which implement letrec as letrec*, and how they handle internal defines.

--
John Cowan   http://ccil.org/~cowan   cowan@ccil.org
'My young friend, if you do not now, immediately and instantly, pull
as hard as ever you can, it is my opinion that your acquaintance in the
large-pattern leather ulster' (and by this he meant the Crocodile) 'will
jerk you into yonder limpid stream before you can say Jack Robinson.'
        --the Bi-Coloured-Python-Rock-Snake

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