Zipper-based File/Operating system with threading and exceptions all realized via delimited continuations. There are no unsafe operations, no GHC (let alone) Unix threads, no concurrency problems. Our threads can't even do IO and can't mutate any global state - and the type system sees to it.
git clone https://github.com/jkarni/ZipperFS
cd ZipperFS
cabal install
$ ghci
GHCi, version 8.0.2: http://www.haskell.org/ghc/ :? for help
Prelude> :load src/ZFS.hs src/ZipperM.hs
[1 of 2] Compiling ZipperM ( src/ZipperM.hs, interpreted )
[2 of 2] Compiling ZFS ( src/ZFS.hs, interpreted )
...
*ZFS> main' fs1
Entering the osloop<socket: 11>
then, in another terminal
telnet localhost 1503
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
/> help
Commands: quit, cd, ls, cat, next, mkdir, touch, echo, rm, mv, cp, help, commit, refresh
This code is in the public domain.