Hi Jason! 2008/12/22 Jason Dusek :

So an iteratee is not like a cursor because it does not "own" the collection -- it just tells us how to step it. The enumerator "owns" the collection and provides a way to scope resource use?

Iteratee does not know anything about resources, it doesn't need to. It is just a function which, given an input stream (which is either EOF, block of data or an IO error string), decides what to do, one of: * yield with some (useful) results (and with the rest of the input) * request more input by returning a continuation The enumerator on the other hand, decides when to open the resource (a file, for example), when to close it, and how to "step" through it. Iteratee only gets the fruits of this hard work. :)

it just tells us how to step it

I would say that it just tells us how to react to various forms of input. :) This is much like the function you pass to foldr. I hope this clarifies iteratees a bit (and that my understanding is correct). Cheers, Artyom Shalkhakov.

Jason Dusek schrieb:

I'm taking a stab at composable streams, starting with cursors. I managed to make a derived cursor today -- as I work through this stuff, I hope to understand Iteratee/Enumerator better.

How about a wiki page on the roles of enumerators and iteratees, best explained using a simple example?

Jason Dusek schrieb:

Henning Thielemann wrote:

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Jason Dusek schrieb:

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I'm taking a stab at composable streams, starting with cursors. I managed to make a derived cursor today -- as I work through this stuff, I hope to understand Iteratee/Enumerator better. How about a wiki page on the roles of enumerators and iteratees, best explained using a simple example?

At present, I am not totally convinced of Iteratee/Enumerator. Why aren't there any functor instances anywhere? Why do filestreams and lists present distinct interfaces? A stream computation is a stream computation; the effect of pulling an item off the stream and handling it is sequenced in these computations so it seems like a monad transformer is in order. So I am just going to keep trying until I can make that transformer.

I have put essentially Oleg's explanation to the Wiki: http://haskell.org/haskellwiki/Enumerator_and_iteratee