Re: [Haskell-cafe] questions on lazy pattern, StateT monad

Am Donnerstag, 24. November 2005 21:52 schrieb Fan Wu:

...

They cannot belong to the same monad. If s is the state type and m1' and m2' belong to the monad m then m1 and m2 belong to the monad StateT s m.

I know it looks insane, I'm just trying to make a recursive case of it: technically it's still possible to have a StateT monad as the m in "StateT s m" right?

Yes, but this StateT type application cannot be equal to the outer StateT type application because this would result in an infinite type which Haskell doesn't support. Example: StateT Int (StateT Int (StateT Int ...))

Thanks, Fan

Best wishes, Wolfgang