I used to love F# before .NET Core, but then it was broken for two years for any sane design time experience on Core. I even wrote some rant about it with speci

I used to love F# before .NET Core, but then it was broken for two years for any sane design time experience on Core. I even wrote some rant about it with specific concerns I had (http://hotforknowledge.com/2016/10/19/4-functional-for-thought-imperative-for-hacking/ http://hotforknowledge.com/2016/10/19/4-functional-for-thoug...). Two years later.. and very recently the .NET Core story started to work well, tooling improved to quite workable state, and in combination with C# it's very strong mix of practicality/performance + complex flexible abstractions and correctness. Over that time F# has added quite a lot of low-level performance features (on par with C# - Span/Memory<T>, ref structs, struct tuples/unions, voidPtr, etc) and they just work. Build time is probably the main concern now, I have to disable building F# projects when they are in a solution but not touched because even on i7-8700/16GB it's very noticeable. Two weeks ago I needed text parser and picked familiar FParsec. It's one of the fastest one in .NET (including C# ones) and is a mix of C# for low-level stuff and F# for powerful abstractions. I refactored it quite substantially and tooling was finally nice. But my attempts to micro-optimize it yielded only in substantially reduced GC due to the support of value structs and Span<T>, throughput was already quite optimal from .NET perspective (only c.<5% gain probably due to GC), so if used with care F# could be as fast as C# (which BTW is native-like fast when also used with care). I believe such mix is the winning combination: C# is best for low-level high performance stuff, F# is best for complex things such as recursive data structures, analytics and so one. My big concern is that F# community is great but often F#-only focused, e.g. reinventing existing C# libraries just because it's not F#. This isolationism from .NET as a uniform platform led for example to things such as F#'s `async` is better than Task Parallel Library (C#'s async/await machinery) in theory/design, but TPL is so much superior is usability, performance and deep platform integration but F# cannot use it directly. Without native TPL `task{}` F# is not a fully-featured .NET Core citizen but a niche language for specific tasks where it shines, e.g. to write a AST parser for a new query language. Sad that MSFT invests so little in F#, but the language is definitely is alive, is improving and is worth using.