Nim and Haxe share many things. To your list I would add:
- a powerful macro system
where they differ is :
- Nim generic is template based, which gives you more power
- Nim has no real working OOP yet, but you can create OOP easily with the macro system
- Nim generics support static[T] which is nice
- Nim has build in yield in the iterator
- Haxe is much mature and reaches version 4. Nim is struggling to reach version 1
- Haxe has pattern matching build in. Nim does this with macro and libraries
- Haxe has Enum as ADT, Nim has object variants. I like Haxe approach much more.
- Nim allows more low-level programming. you can switch off GC, have manual memory management and have different GCs available (ref counted, mark and sweep, boehm, real time).
- Haxe has a static analyzer and very good inliner. Nim relies on the backend compiler to do the job until now. When targeting C or C++ Nim code is in general a bit faster than Haxe (less overhead, better memory handling, no Dynamic). On JS I would claim that Haxe is better
- Haxe has a much more options for the backend
So its a matter what you are doing. For system level programming I would choose Nim. For UI, client side, cross platform or games I would choose Haxe. Both are nice and I use both.