Re: [Haskell-cafe] A Monad for on-demand file generation?

Hi, thanks again for you input. Just one small remark: Am Dienstag, den 01.07.2008, 14:52 -0700 schrieb Ryan Ingram:

On 7/1/08, Joachim Breitner wrote:

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Am Montag, den 30.06.2008, 16:54 -0700 schrieb Ryan Ingram:

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1) unsafeInterleaveIO seems like a big hammer to use for this problem, and there are a lot of gotchas involved that you may not have fully thought out. But you do meet the main criteria (file being read is assumed to be constant for a single run of the program).

Any other gotcha? Anyways, is this really worse than the similary lazy readFile? Using that would not safe the call to open, but at least the reading and processing, in the same situations.

Well, you're also (from your description) probably writing some tracking information to an IORef of some sort. That can happen in the middle of an otherwise pure computation, and it's difficult to know exactly when it'll get triggered, due to laziness. You can probably make it work :)

Well, for the tracking information, I can do it purely, by copying code from StateT (or WriterT or ReaderT, I’m not sure :-)), and adapting slightly (e.g. the (>>) optimization). So besides unsafeInterleaveIO, no “bad, unpure stuff” should be necessary. I think I’ll put my ideas to code soon and post it here. Greetings, Joachim -- Joachim Breitner e-Mail: mail@joachim-breitner.de Homepage: http://www.joachim-breitner.de ICQ#: 74513189 Jabber-ID: nomeata@joachim-breitner.de