Deep map?

I often write several levels of map: map (map (...

Is it possible to implement a generic “deepMap” that maps the innermost or arbitrarily nested functors?

Possible inspiration: http://okmij.org/ftp/Haskell/typecast.html#deepest-functor

[adz]

You are dealing with two monads - async and result… So monad transformers are just a type to help combine them.

I have ResultT<Async<Result<_>>> because I am combining with Async. It seems a bit backwards as the Result is inner. The ResultT can combine with any other monad.

I wrote notes as I started to feel comfortable with them, because I also struggled to comprehend them for a long time… See here http://adzdavies.blogspot.com/2019/12/monadtransformers-lets-look-at-resultt.html

[gusty]

There is Compose which allows you to compose arbitrary functors

https://github.com/fsprojects/FSharpPlus/blob/33fa3411cb080fc70d8b4ad4f71e16d63bc82128/src/FSharpPlus/Monoids.fs#L93-L114

But what you want is to avoid wrapping / unwrapping.

We could add a set of map2 mapN functions, additionally/alternatively we could add some funny versions of applicative operators like <!!> and <**>.

Definitely it’s something to consider.

A full generic deepmap over an arbitrary number of functors is quite complex to encode, it might be possible I have to give it a try.

Then if it works we have to see how is type inference, my feeling is that with the current state of the F# compiler it won’t be amazing.