On Thu, Jul 30, 2009 at 7:06 PM, Phil
Hi,
I've hit a brick wall trying to work out, what should be (and probably is!) a simple problem.
I have a StateT stack (1 State monad, 2 StateT transformers) which works fine and returns the result of the outer monad. I thought I understood this fine, but perhaps not. My understanding is that the result returned by the inner-most monad is always 'transformed' by the outer monads and thus the result you get is that computed in the outer transformer.
What I would do is not use transformers - I would have computations of type 'State MyState a' where 'MyState' would be something like: data MyState = MyState { component_one :: TypeOne , component_two :: TypeTwo , component_three :: TypeThree } instead of three separate transformers/monads for each data type. I would then have helper functions: getThingOne :: State MyState TypeOne setThingOne :: TypeOne -> State MyState () modifyThingOne :: (TypeOne -> TypeOne) -> State MyState TypeOne etc. You'll want to pick better names for your types and helper functions as suits your program. Antoine