Re: [Haskell-cafe] type checking that I can't figure out ....

Am Mittwoch 03 Juni 2009 06:12:46 schrieb Michael Snoyman:

I made two changes:

1. You had the arguments to M.lookup backwards. 2. lookup does not return any generalized Monad, just Maybe (I think that should be changed).

Data.Map.lookup used to return a value in any monad you wanted, I believe until 6.8 inclusive. I don't think it's going to change again soon.

I added the simple liftMaybe function to convert the Maybe result into something that will work with your state monad.

Michael