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
