Hello Peter,
This is a classic problem with the normal monad type class. You can
achieve this with "restricted monads", but there is a bit of tomfoolery
you have to do to get do-notation support for them.
Here is some relevant reading:
- http://okmij.org/ftp/Haskell/types.html#restricted-datatypes
- http://hackage.haskell.org/package/rmonad-0.4.1
Cheers,
Edward
_______________________________________________
Haskell-Cafe mailing list
Haskell-Cafe@haskell.org
http://www.haskell.org/mailman/listinfo/haskell-cafe
