Lazy IO is a complete disaster for "interactive IO", such as network and process IO. Moreover, it's somewhat of a failure even for non- interactive IO such as the use case you described, because it's very easy for partial evaluation to lead to unclosed files and lazy evaluation to lead to delayed resource acquisition. I can imagine a few use cases that might benefit from it, but the evidence suggests that most developers trying to solve "real world" problems work extra hard to get their programs working properly with lazy IO. Elsewhere, laziness can be a real boon, so I don't understand your question, "Why have laziness in Haskell at all?" Regards, John A. De Goes N-BRAIN, Inc. The Evolution of Collaboration http://www.n-brain.net | 877-376-2724 x 101 On Mar 2, 2009, at 6:03 PM, Henning Thielemann wrote:
On Mon, 2 Mar 2009, John Lato wrote:
Hello,
I am not a super-geek (at least, not compared to others on this list), but I'll take a try at this anyway. The benefits of iteratees mostly depend on differences between lazy and strict IO (see ch. 7 of Real World Haskell for more on this).
Maybe a good text for http://www.haskell.org/haskellwiki/Enumerator_and_iteratee ?
[a]. Say I have a chain of functions: read a file, parse it into a tag soup, parse that into an XML tree, transform that tree, format
While I think that the Iteratee pattern has benefits, I suspect that it can't be combined with regular lazy functions, e.g. of type [a] - that into a string, write that to a file, and all of these functions are written in a lazy way, which is currently considered good style, I can't use them in conjunction with iteratees. This means, almost all Haskell libraries have to be rewritten or extended from lazy style to iteratee style. The question for me is then: Why having laziness in Haskell at all? Or at least, why having laziness by default, why not having laziness annotation instead of strictness annotation.
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