Re: [Haskell-cafe] ANNOUNCE: iterIO-0.1 - iteratee-based IO with pipe operators

On Fri, May 6, 2011 at 6:46 AM, David Virebayre wrote:

2011/5/6 Ertugrul Soeylemez :

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David Mazieres wrote:

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Please enjoy.  I'd love to hear feedback.

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Thanks a lot, David.  This looks like really good work.  I'm using the 'enumerator' package, and looking at the types your library seems to use a similar, but more complicated representation.  Is there any particular reason, why you didn't base your library on an existing iteratee package like 'enumerator'?

David has documented some design decisions in http://hackage.haskell.org/packages/archive/iterIO/0.1/doc/html/Data-IterIO....

Perhaps you may find some answers there.

He says that enumerator's Iteratee doesn't have special support for pure Iteratees. When he says that the iteratee package doesn't have special support for control messages, the same applies for enumerator as well. He also says that enumerator can't distinguish failures from iteratees and enumeratees. He also says that the enumerator package's Enumerators aren't iteratees, only iterIO's enumerators are. Well, that's not what I'm reading: -- from enumerator package newtype Iteratee a m b = Iteratee {runIteratee :: m (Step a m b)} type Enumerator a m b = Step a m b -> Iteratee a m b type Enumeratee ao ai m b = Step ai m b -> Iteratee ao m (Step ai m b) -- from iterIO package newtype Iter t m a = Iter {runIter :: Chunk t -> IterR t m a} type Inum tIn tOut m a = Iter tOut m a -> Iter tIn m (IterR tOut m a) type Onum t m a = Inum () t m a The enumerator package's Enumerator *is* an iteratee, an so is its Enumeratee. The only real difference is that iterIO represents enumerators as enumeratees from () to something. In enumerator package terms, that would be -- enumerator packages's enumerator if it was iterIO's :) -- note that Inum's "tIn" and "tOut" are reversed w.r.t Enumeratee "ao" and "ai" type Enumerator a m b = Enumeratee () a m b Whether this representation is better or worse isn't clear for me. Now, one big problem that iterIO has that enumerator hasn't, is that iterIO is a *big* library with many dependencies, including OpenSSL. IMHO, that package should be split into many others. So, in the enumerator vs. iterIO challenge, the only big differences I see are: a) iterIO has a different exception handling mechanism. b) iterIO can have pure iteratees that don't touch the monad. c) iterIO's iteratees can send control messages to ther enumerators. d) iterIO's enumerators are enumeratees, but enumerator's enumerators are simpler. e) enumerator has fewer dependencies. f) enumerator uses conventional nomenclature. g) enumerator is Haskell 98, while iterIO needs many extensions (e.g. MPTC and functional dependencies). Anything that I missed? The bottomline: the biggest advantage I see right now in favor of iterIO is c), although it still has the problem that you may get runtime errors if you send the wrong control message. However, right now e) and g) may stop many users of enumerator from porting to iterIO, even if they like its approach. Cheers! =) -- Felipe.