Blocking IO & FIFOs

Hi all,

I am developing a coroutine-like interface to Bash.

  http://hpaste.org/76523

The idea is that one can send multiple "queries" to an
interpreter and then collect the results of each query. How do
we know when Bash is done with each query? Waiting for "no more
output" seems ambiguous; so the way CoBash works is:

  * Each query gets a tmp dir with two named pipes in it.
  * The query is wrapped in redirections to the pipes.
  * The pipes are removed when the query completes.

This does work, sort of:

  +Prelude> :load CoBash.hs
  [1 of 1] Compiling CoBash           ( CoBash.hs, interpreted )
  Ok, modules loaded: CoBash.
  *CoBash> tuple <at> (i,o,e,p) <- start
  e :: Handle
  i :: Handle
  o :: Handle
  p :: ProcessHandle
  tuple :: (Handle, Handle, Handle, ProcessHandle)
  *CoBash> query tuple "for n in {1..4}; do sleep 1; echo $n; done"
  ("1\n2\n3\n4\n","")
  it :: (ByteString, ByteString)