On Tue, Feb 27, 2018 at 12:02:49PM +0100, Jeroen Bransen wrote:
In my concrete case I think a profunctor is indeed the thing I was looking for If you're willing to share your datatype I may be able to help determine exactly what sort of thing it is. I have extensively explored the place of profunctors :) http://hackage.haskell.org/package/progress-reporting-1.1.0/docs/Control-Mon...
It's a class of functions (that may run in some monadic context) for which we can report progress. I can lift certain types of functions to this space (those that construct items of a list, or those that report their own progress in some way), and then these compose in several ways. Obviously having the first and second combinators from arrows comes in handy.
The type in question is WithProgress data WithProgress m a b where Id :: WithProgress m a a WithProgressM :: ((Double -> m ()) -> a -> m b) -> WithProgress m a b Combine :: WithProgress m b c -> WithProgress m a b -> WithProgress m a c SetWeight :: Double -> WithProgress m a b -> WithProgress m a b Is this definition of arr somehow unsatisfactory? arr :: Applicative m => (a -> b) -> WithProgress m a b arr f = WithProgressM (\_ a -> pure (f a)) NB that if you implement Category and Profunctor then you automatically get arr (\f -> lmap f id). Tom