Jinwoo Lee wrote:
Hi,
Recently I wrote a code that uses readline library (System.Console.Readline). I had to maintain a state (file path) and do IO throughout the code, so I decided to use StateT monad.
The problem was that in order to retrieve the current state (file path) inside the handler that had been registered by using bindKey function of readline, I had to resort back to using IORef rather than using the state stored in the StateT monad. It's because the handler for bindKey should have the type of Int -> Char -> IO Int.
[snip]
Is there any way in which I can do without IORef in tabHandler and commandLoop (written in red and bold, if you can see)?
Probably not, but this is worth a read if you want to hide the plumbing behind the scenes a bit: "Monadic tunnelling: the art of threading one monad through another" http://www.haskell.org/pipermail/haskell-cafe/2007-July/028501.html Claude -- http://claudiusmaximus.goto10.org