This is probably less readable than it has to be due to the lack of whitespace. I don't know the language (Scala?), but I don't think it's too hard to work it out. First, the '[F[_], A, B]' part are type parameters, where I assume the 'F[_]' part is just a bad notation for a type of kind '* -> *' (i.e. a higher-ranked type). The next value parameter has type 'Option[A]', and after that we have 'A => F[B]'. This confirms my suspicion that 'F' is a higher-ranked type - and probably a functor or something. The 'f' parameter is a function for converting a value of type 'A' into a value of type 'F[b]', which looks like it's tranforming a value and putting it into a functor or something. The final '(implicit F: Applicative[F])' hints at deep problems in the language, but I think it basically just says something like 'the higher-rank type F must implement the trait/typeclass/whatever Applicative'.

That's the type. The expression makes little sense to me, but I suspect you removed a bunch of dots and maybe some parens, and it should actually look like this:

          fa.map (a => F.map(f(a))(Some(_): Option[B])).getOrElse(F.point(None))

So this function essentially just operates on an option value inside of some functorial context. This seems like a building block function that you might use often, but probably not write very frequently.

(If you didn't remove anything, then I suppose this language has infix 'map' and 'getOrElse' operators. I think that's bad, but it's not related to the type system.)

scala has infix everything ‘operators’. f(x) can be written as f x and f.g(x) can be written as f g x if the parser manages to figure out what it means (I’m sure they phrase that differently)

Idea, I think, is to make the repl look more like a CLI, but it also may be a fight against punctuation.

Its only hard to read because you don't know the language, otherwise, its fairly straightforward. Although the Applicative type would require some research. I would much rather use a language like this, that can create enough abstraction to enforce consistency throughout the codebase, rather than relying on boilerplate conventions. Just had a bug this week in Go where a previously defined "err" variable was re-used instead of creating yet another "err" variable, which caused the actual error never to get checked.

This function is certainly hairy, but its use in the codebase might very well be intuitive and simplify code that would otherwise be way less expressive. I personally think it can be worth it.

Transform fa using f, collecting the results as an option