LOlouthy·Jan 5, 2026
Aww, thanks Mike! And thank you for the contributions and suggestions too :)
> At this point basically everyone has been exposed to the concept of `Option/Result/Either/etc. and discussions typically end up revolving around the aesthetics of exception throwing vs. method chaining vs. if statements etc. without any concept of the bigger picture.
I think this is a really important point. 12 years ago I created a project called 'csharp-monad' [1], it was the forerunner to language-ext [2], which I still keep on github for posterity. It has the following monadic types:
Either<L, R>
IO<T>
Option<T>
Parser<T>
Reader<E,T>
RWS<R,W,S,T>
State<S,T>
Try<T>
Writer<W,T>
One thing I realised after developing these monadic types was that they're not much use on their own. If your List<T> type's Find method doesn't
Read the rest
return Option<T>, then you haven't gained anything.
I see others on here are taking a similar journey to the one I took over a decade ago. There's an obsession over creating Result types (Either<L, R> and Fin<A> in language-ext, btw) and the other basic monads, but there's no thought as to what comes next. Everyone of them will realise that their result-type is useless if nothing returns it.
If you're serious about creating declarative code, then you need an ecosystem that is declarative. And that's why I decided that a project called "csharp-monad" was too limiting, so I started again (language-ext) and I started writing immutable collections, concurrency primitives, parsers, and effect systems (amongst others). Where everything works with everything else. A fully integrated functional ecosytem.
The idea is to make something that initially augments the BCL and then replaces/wraps it out of existence. I want to build a complete C# functional framework ecosystem (which admittedly is quite an undertaking for one person).
I'm sometimes a little wary about going all in on the evangelism here. C# devs in general tend to 'stick to what they know' and don't always like the new, especially when it's not idiomatic - you can see it in a number of the sub-threads here. But I made a decision early on to fuck the norms and focus on making something good on its own terms.
And for those that wonder "Why C#?" or "Why not F#?", well C# has one of the best compilers and tooling ecosystems out there, it's got an amazing set of functional language features, it will have ADTs in the next version, and it has a strong library ecosystem. It also has the same kind of borrow checker low level capability as Rust [3]. So as an all-rounder language it's quite hard to beat: from 'to the metal bit-wrangling', right the way up to monad comprehensions. It should be taken more seriously as a functional language, but just generally as a language that can survive the turmoil of a long-lived project (where mostly you want easy to maintain code for the long-term, but occasionally you might need to go in and optimise the hell out of something).
My approach will piss some people off, but my aim is for it to be like the Cats or Scalaz community within the larger Scala community.
It's certainly a labour of love right now. But, over a decade later I'm still enjoying it, so it can't be all bad.
(PS Mike, I have new highly optimised Foldable functionality coming that is faster than a regular C# for-loop over an array. Watch this space!)
[1] https://github.com/louthy/csharp-monad
[2] https://github.com/louthy/language-ext
[3] https://em-tg.github.io/csborrow/