If I run the following program, it never prints "done". If I uncomment the commented line, it does. import Prelude hiding (catch) import Control.Exception import System.Process import System.IO demo = do putStrLn "starting" (inp,out,err,pid) <- runInteractiveCommand "nonesuchcommand" putStrLn "writing to in on bad command" hPutStr inp "whatever" -- putStr "flushing" hFlush inp `catch` \e -> do print e; return () putStrLn "done" main = demo `catch` \e -> do print e; return () On my machine the output is: $ runhaskell test.hs starting writing to in on bad command $ It appears to exit at the hFlush call. (hClose has the same behavior.) I find this surprising -- I'd expect, even if I'm using an API incorrectly, to get an exception.