Re: Unsafe hGetContents
Excerpts from Simon Marlow's message of Tue Oct 06 14:59:06 +0200 2009: On 03/10/2009 19:59, Florian Weimer wrote: * Nicolas Pouillard: Excerpts from Florian Weimer's message of Wed Sep 16 22:17:08 +0200 2009: Are there any plans to get rid of hGetContents and the semi-closed handle state for Haskell Prime? (I call hGetContents unsafe because it adds side effects to pattern matching, stricly speaking invalidating most of the transformations which are expected to be valid in a pure language.) Would you consider something like [1] as an acceptable replacement? [1]: http://hackage.haskell.org/package/safe-lazy-io It only addresses two known issues with lazy I/O, doesn't it? It still injects input operations into pure code not in the IO monad. While what you say is true, and I've complained about the same thing myself in the past, it turns out to be quite difficult to demonstrate the unsafety. Try it! Here's the rules. - write a program that gives different results when compiled with different optimisation flags only. (one exception: you're not allowed to take advantage of -fno-state-hack). - Using exceptions is not allowed (they're non-determinstic). - A difference caused by resources (e.g. stack overflow) doesn't count. - The only unsafe operation you're allowed to use is hGetContents. - You're allowed to use any other I/O operations, including from libraries, as long as they're not unsafe, and as long as the I/O itself is deterministic. The reason it's hard is that to demonstrate a difference you have to get the lazy I/O to commute with some other I/O, and GHC will never do that. If you find a way to do it, then we'll probably consider it a bug in GHC. You can get lazy I/O to commute with other lazy I/O, and perhaps with some cunning arrangement of pipes (or something) that might be a way to solve the puzzle. Good luck! Oleg's example is quite close, don't you think? URL: http://www.haskell.org/pipermail/haskell/2009-March/021064.html Cheers, -- Nicolas Pouillard http://nicolaspouillard.fr ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Unsafe hGetContents
Excerpts from Simon Marlow's message of Mon Sep 21 11:41:38 +0200 2009: On 16/09/2009 21:17, Florian Weimer wrote: Are there any plans to get rid of hGetContents and the semi-closed handle state for Haskell Prime? (I call hGetContents unsafe because it adds side effects to pattern matching, stricly speaking invalidating most of the transformations which are expected to be valid in a pure language.) There is no current proposal for this, no. Feel free to start one; information about the process for Haskell Prime proposals is here http://hackage.haskell.org/trac/haskell-prime/wiki/Process An alternate proposition (instead of removing it) would to to move it to System.IO.Unsafe. -- Nicolas Pouillard http://nicolaspouillard.fr ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Unsafe hGetContents
Excerpts from Simon Marlow's message of Mon Sep 21 11:52:41 +0200 2009: On 17/09/2009 13:58, Nicolas Pouillard wrote: Excerpts from Florian Weimer's message of Wed Sep 16 22:17:08 +0200 2009: Are there any plans to get rid of hGetContents and the semi-closed handle state for Haskell Prime? (I call hGetContents unsafe because it adds side effects to pattern matching, stricly speaking invalidating most of the transformations which are expected to be valid in a pure language.) Would you consider something like [1] as an acceptable replacement? [1]: http://hackage.haskell.org/package/safe-lazy-io I rater like this as a workaround for the most common practical problems with lazy I/O, those of resource control. It doesn't address the deeper concern that lazy I/O requires a particular evaluation order and is therefore a bit warty as a language feature When using safe-lazy-io we no longer rely (or a lot less) on the evaluation order (assuming you mean the order of side-effects). Since the way of combining the different inputs is statically chosen by user. - implementing lazy I/O properly in GHC's parallel mutator was somewhat tricky. I'm not of the opinion that we should throw out lazy I/O, but it's still a problematic area in Haskell. Maybe the 'unsafeGetContents' feature required by a safe-lazy-io would be less problematic, in particular it does not have to ignore exceptions. Best regards, -- Nicolas Pouillard http://nicolaspouillard.fr ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
Re: Unsafe hGetContents
Excerpts from Florian Weimer's message of Wed Sep 16 22:17:08 +0200 2009: Are there any plans to get rid of hGetContents and the semi-closed handle state for Haskell Prime? (I call hGetContents unsafe because it adds side effects to pattern matching, stricly speaking invalidating most of the transformations which are expected to be valid in a pure language.) Would you consider something like [1] as an acceptable replacement? [1]: http://hackage.haskell.org/package/safe-lazy-io -- Nicolas Pouillard http://nicolaspouillard.fr ___ Haskell-prime mailing list Haskell-prime@haskell.org http://www.haskell.org/mailman/listinfo/haskell-prime
