Hi Oleg
This approach has the same flaw as your "Simple IO Regions" code. The
typing prevents you from constructing actions involving a handle outside
the region of the handle, but not from constructing actions in the
region and using them outside. Without the rank-2 types we can use
runIOM, and should to take advantage of the Typeable1 IO instance.
--saving this message as IORegionsTest98Fail.lhs
>module IORegions98TestFail where
>import IORegions98
>import Monad
>testMinus1 = join $ runIOM $ withFile "/etc/motd" $
> return . runIOM . qGetChar
Which fails like this:
___ ___ _
/ _ \ /\ /\/ __(_)
/ /_\// /_/ / / | | GHC Interactive, version 6.4, for Haskell 98.
/ /_\\/ __ / /___| | http://www.haskell.org/ghc/
\____/\/ /_/\____/|_| Type :? for help.
Loading package base-1.0 ... linking ... done.
Compiling IORegions98 ( ./IORegions98.hs, interpreted )
Compiling IORegions98TestFail ( IORegions98TestFail.lhs, interpreted )
Ok, modules loaded: IORegions98TestFail, IORegions98.
*IORegions98TestFail> testMinus1
Loading package haskell98-1.0 ... linking ... done.
*** Exception: /etc/motd: hGetChar: illegal operation (handle is closed)
I think something like the Simple IO Regions code can be made to work
with a more complicated representation of the marks set. I'll see if I
can post a system of my own in a few days, rather than just test cases
for yours.
Brandon
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