On Mon, 27 Sep 2004 14:11:30 +0100, Jon Harrop <jon@jdh30.plus.com> wrote:
> > For the writter of the function there is a big difference, especially
> > if it has to write the specialized versions.
> 
> The equivalent to the writer of fold is the writer of an iterator. You have to
> write specialized versions for each type of iterator just as you would have
> to write your own fold.

That's why I said iterators are another level of abstraction. The
difference is that after you write the iterators code for a new
sequence-like data structure all the "generic" functions, not only
fold but also map and others, will automagically work on them. The
simplest form of an "iterator" is implementing  a "next" function for
all sequences (although in this situation it is more of an
"enumeration").

regards,
 radu

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