On Fri, 2013-08-23 at 08:06 +0000, oleg@okmij.org wrote:
It will arbitrarily pick the first match in the former and fail to compile in the latter case. Of course we can have duplicate layers. In that case, the dynamically closest handler wins -- which sounds about right (think of reset in delimited control).
Did anyone ever consider using type-level literals (strings) to 'name' effects (or transformer layers when using monad stacks)? A stupid example (OTOH) could be updateStats :: (Member (State "min" Int) r, Member (State "max" Int) r) => Int -> Eff r () updateStats i = do min <- askMin max <- askMax when (i < min) $ putMin i when (i > max) $ putMax i where askMin :: Member (State "min" Int) r => Eff r Int askMin = ask putMax :: Member (State "max" Int) r => Int -> Eff r () putMax = put -- askMax, putMin accordingly Using constraint synonyms/ConstraintKinds (e.g. type StateMax r = Member (State "max" Int) r) might reduce some notation overhead. Just a thought. Nicolas