[Haskell-cafe] Re: Left fold enumerator - a real pearl overlooked?

Gü?nther Schmidt gue.schmidt at web.de
Sun Mar 1 19:31:02 EST 2009

Hi everyone,

after reading all the responses I would like to ask someone, anyone, to 
kind of summarize the merits of the left-fold-enumerator approach.

 From all that I read so far about it all I was able to gather was that 
it has significance but I'm still not even sure what for and what not for.

Apparently Oleg has done various CS work, this particular piece just 
being one. But he also broaches the topic at very high level, ok, too 
high for me, ie. no CS or higher math background.

Would one of the super geeks please summarize it up? (In RWH kind of 
style if possible)


John Lato schrieb:
> Hi Don,
> Would you please elaborate on what features or capabilities you think
> are missing from left-fold that would elevate it out of the special
> purpose category?  I think that the conception is so completely
> different from bytestrings that just saying it's not a bytestring
> equivalent doesn't give me any ideas as to what would make it more
> useful.  Since the technique is being actively developed and
> researched, IMO this is a good time to be making changes.
> Incidentally, in my package I've made newtypes that read data into
> strict bytestrings.  It would be relatively simple to use
> unsafeInterleaveIO in an enumerator to create lazy bytestrings using
> this technique.  I don't see why anyone would want to do so, however,
> since it would have all the negatives of lazy IO and be less efficient
> than simply using lazy bytestrings directly.
> Cheers,
> John
> On Sat, Feb 28, 2009 at 10:54 PM, Don Stewart <dons at galois.com> wrote:
>>> There are a few iteratee/enumerator design questions that remain,
>>> which Oleg and others would like to explore more fully.  The results
>>> of that research will likely find there way into this library.
>> I agree. There's no left-fold 'bytestring' equivalent. So it remains a
>> special purpose technique.
>> -- Don

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