For the past months I have spent most of my time on .NET using C# but I also would have liked to use Common Lisp on it. I do not know of a CL implementation for .NET and I read some time ago that probably doing one is not that easy, as this answer in Stack Overflow states. I wonder if it is related to floating-point exceptions (if someone knowledgeable in this area would like to comment, I thank you in advance!).

Anyway, I decided to look more carefully to see if I could find something and discovered four projects. Initially I was a bit excited that probably there is something after all. But after a more careful observation, they are far from what you would expect or want. For future reference:

The first project, ClearLisp, looked promising but it’s not even CL. Looking at the documentation you realize some differences between it and CL. Also, the project shows no sign of life since 2008 and after playing with it a little bit, it’s far from a modern CL implementation. The second one is not a proper implementation since it’s using ABCL and IKVM. The third one seems to be a way to connect ECL to .NET and uses it as a scripting language. The fourth one also looks more like an attempt than a real implementation (I didn’t explore it).

In the end, there is really no CL implementation for .NET or even one that compiles to bytecode. There is RDNZL which lets you call .NET libraries from a Common Lisp application. However, it’s not the same as having a real implementation.

Furthermore, the state of Lisp-languages on .NET is not much better since you can find lots of half-baked, abandoned languages/implementations or just without real followers (for example, L#, Yarr, dotlisp, Common Larceny, ayaka and others). The major exceptions are probably IronScheme and Clojure. And even the CLR Clojure implementation is just playing catch-up with the Java one.

The set of programmers interested in CL (or even just Lisp) and .NET is probably extremely small and thus, the current state of affairs. However, I feel that this can still be a good area of opportunity if done right.

Edit 1: zvrba on reddit explains the floats issue, which I put here:

The problem with CLR floating-point is that the virtual machine supports only one floating-point type, double (64-bit). (32-bit) float is a storage format only, so in some cases double rounding occurs, leading to results that differ from “proper” float calculations by 1 ulp.

Edit 2: clausb also on reddit pointed out to a list of Lisp projects on .NET he compiled before.

Disclaimer: the views and opinions expressed on this blog are my own and not those of my employer.