[Haskell-cafe] Re: Handles with their IOMode in their type
Brandon S. Allbery KF8NH
allbery at ece.cmu.edu
Wed Dec 9 21:00:00 EST 2009
On Dec 9, 2009, at 16:51 , Bas van Dijk wrote:
> I will change the types to:
> stdin :: Handle ReadMode
> stdout :: Handle WriteMode
> stderr :: Handle WriteMode
> Or are there scenarios where people want to write to stdin or read
> from stdout or stderr?
These situations *do* come up; the controlling terminal for a program
is open read/write on all 3 file descriptors initially, ands programs
like more/less/pg rely on this and do their I/O on stdout.
Additionally, on *BSD pipes are actually socketpairs and therefore
bidirectional, and a small number of programs rely on this.
But I would not do that by default, just expose a way for programs to
make it so if they wish.
(Hm, just discovered that the System.Posix.IO wrapper for fcntl() does
*not* expose the part of the result of F_GETFL that reports the open
mode. Boo hiss.)
brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery at kf8nh.com
system administrator [openafs,heimdal,too many hats] allbery at ece.cmu.edu
electrical and computer engineering, carnegie mellon university KF8NH
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