If I want to change the return type of the `refactorMe` function from an `Option` to just the value `x`, all calling functions change their type automagically - no need to change every method signature, as in C#. Same for input arguments.

Big time saver.

2/2

Or reference system? But then I would assume rotations would also be a thing.

A feature more from F# 😅

type Fruit = Apple | Banana

let a = Fruit.Apple
let b = Banana

Both are possible.

I'm obviously wrong. Docu:
> If either AsyncResult resolves to an error, then the other is cancelled and only the first error is returned.

I don't know. Probably not.

Use case: make my coworker cry in agony! 😂

And in case you wonder why the whole code is in a method, not a function: The facades to our subsystems are modelled with classes, not modules because they act as a composition root for the subsystem and need to hold state. This makes the design more consistent in our mixed C# and F# codebase.

4/4

return!: call a function that returns Result or is async or both and return the return value directly.
|!>: custom operator for |> Async.map

3/4

parallelAsyncResult: allows handling errors and asynchronous parallelism
let! x: await the call and assign the result to the value x
and! execute in parallel and await and assign
AsyncResult.requireSome: check that we have a value otherwise return an Error, which acts like an early return

2/4

If it makes our builds faster (I couldn't test it yet), then Type subsumption cache.

To be fair, the new stuff in F# would probably not make a good presentation. It's better to read about it in the release notes.
There is also an F# talk on the community day.

A shorter one: leanpub.com/essential-fs...

Or start with the official documentation: learn.microsoft.com/de-de/dotnet...

Great book: www.manning.com/books/get-pr....

Great exercises: exercism.org/tracks/fsharp