Re: Scheme style auto-resizing hashtable (fwd)

[mike@olan.com (Michael N. Livshin)]

Maciej Stachowiak <mstachow@mit.edu> writes:

[ snip ]

> Iterators are very un-Schemely, IMO, Scheme is not in the business of
> telling you how to iterate.

Huh?

According to one classification I've seen, there are two kinds of iterators:

1) "Internal" iterators - those that _do_ tell you how to iterate.
Scheme has, for example, `for-each', which is an internal list iterator.

2) "External" iterators - those that _do_not_ tell you how to iterate.
What is so un-Schemely about the following snippet?

--------------->8 cut cut 8<-----------------

(define (p e)
  (display e)
  (newline))

(define l-range (list->i-range '(la lb lc)))
(define v-range (vector->i-range '#(va vb vc)))

(for-each/i-range p (car l-range) (cdr l-range))

 ==> la
     lb
     lc

(for-each/i-range p (car v-range) (cdr v-range))

 ==> va
     vb
     vc

--------------->8 cut cut 8<-----------------

Here is the readable definition of `for-each/i-range':

(define (for-each/i-range proc first last)
  (let loop ((current first))
    (if (not (i=? current last))
        (begin
          (proc (i-ref current))
          (loop (++i current))))))

And here is the actual definition (uglier but not so garbage-generating):

(define (for-each/i-range proc first last)
  (let loop ((current (clone-i first)))
    (if (not (i=? current last))
        (begin
          (proc (i-ref current))
          (loop (++i! current))))))

[ snip ]

>  - Maciej

mike.