How does F#'s async really work?

Question

I am trying to learn how async and let! work in F#. All the docs i\'ve read seem confusing. What\'s the point of running an async block with Async

Answer 1

Lots of great detail in the other answers, but as I beginner I got tripped up by the differences between C# and F#.

F# async blocks are a recipe for how the code should run, not actually an instruction to run it yet.

You build up your recipe, maybe combining with other recipes (e.g. Async.Parallel). Only then do you ask the system to run it, and you can do that on the current thread (e.g. Async.StartImmediate) or on a new task, or various other ways.

So it's a decoupling of what you want to do from who should do it.

The C# model is often called 'Hot Tasks' because the tasks are started for you as part of their definition, vs. the F# 'Cold Task' models.