Re: [Haskell-cafe] Re: Using the ContT monads for early exits of IO ?

On Thu, Jun 10, 2010 at 8:57 PM, Maciej Piechotka wrote:

Error monad seems not to be a semantic solution as we exit on success not failure.

Which is really why the Either monad should not necessarily have Error associations :) If you forget about the fail method, the Monad (Either e) instance doesn't need the e to be an error type. Alternatively, if even Error is more information than you need, you could use MaybeT: http://hackage.haskell.org/package/MaybeT which allows you to just stop. Given you're using it with IO it'd be easy to write a result to an IORef before terminating the computation, so it's of equivalent power, if slightly less convenient.