C# developer (as using it & get paid) here!
Putting back the language porter (noob & failed to port shame) robe: It takes too much work to get a basic bootstrapped mono to keep compiling the new versions which require a working mono on your Haiku, and doesnt work 100%.
Also, since version 5.0 (IIRC), they began to use Roslyn C# compiler, which code doesnt want to work nicely with previous compiler (MCS). So you get a pre 5.0 version than cannot go forward in versions (yay!).
Btw mono sources were huge in quantity and took too long to decompress, compile and delete once you are done with them (probably because i had them in a query enabled partition).
However, mono can be ditched in favor of trying to port .Net Core code, which could be a new source of having C# code on Haiku. But that’s only for code that has been written in either .Net Core or .Net Standard and not previous code (like .Net Framework 3.x or 4.x). Also has no gui, no support of traditional ASP.NET websites, nor… well you get the idea. It still rocks for developing new apps / mvc sites for Linux tho.
That’s what happened.
Real Haiku mono porter Calvin thread: Porting Mono
Amazing blog post of what you can do in Mono previous to 5.0 by calvin: http://minisoc.xyz/HaikuMono/
I doublechecked that on my sources, had some fun, moved to other langs (nodeJS)