Dear Haskell users, I am working on a command-driven tool (::IO ()). If the system invokes itself again, and the system's returned data type would be 'IO a', say (IO Exp) (Expression). tool:: a -> IO() The nested tool invocation returns (IO Exp) to the previous tool. I am using dynamic error exception handling like (throwDyn exp). If I use 'forkIO', then it works for this situation (e.g. IO Exp) but it is not working for 'quit' command (quit the tool:: thread blocked indefinitely) - quit the subtool and return to the previous tool. Any suggestion would be helpful? tool = {tool1, tool2, tool3, ...} tool1:: (IO ()) invoked tool2:: (IO a) may invoked tool3:: (IO a) tool2 is working basically on IO() and if I got the Exp (proved), then return it to the previous tool (say tool1). Thanks in advance, min