On 10 June 2011 06:43, Richard O'Keefe <o...@cs.otago.ac.nz> wrote: > > On 10/06/2011, at 1:11 AM, Erik Hesselink wrote: > > > On Thu, Jun 9, 2011 at 13:40, Neil Davies <semanticphilosop...@gmail.com> > wrote: > >> Anyone out there got an elegant solution to being able to fork a haskell > thread and replace its 'stdin' ? > > > > If you don't mind being tied to GHC you can use hDuplicateTo from > > GHC.IO.Handle [1]. You can also use dupTo from the unix package [2], > > but that ties you to unix-like platforms instead. > > > > Erik > > > > [1] > http://hackage.haskell.org/packages/archive/base/latest/doc/html/GHC-IO-Handle.html#v:hDuplicateTo > > That replaces stdin for *every* Haskell thread. > > > [2] > http://hackage.haskell.org/packages/archive/unix/latest/doc/html/System-Posix-IO.html#v:dupTo > > That alters file descriptor 0 for *every* Haskell thread. > > As I understand the original poster's question, it would be > paraphrased as "can the association between the default input stream > used by getChar and the rest be changed for ONE thread in a Haskell > program by some method that does NOT have any effect on any other > thread in the same OS process". Or to put it another way, "do I > really have to pass a handle around to all these functions in my > thread?" > > And the answer would seem to be "there is no reason in principle > why this *couldn't* be supported, but it *isn't*; there are no > C-style thread-local global variables. Yes, you do have to pass > that handle around more than you would like to." > > Could implicit parameters be used for this purpose?
http://www.haskell.org/ghc/docs/7.0.3/html/users_guide/other-type-extensions.html Alexander
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