OCaml vs Nim

Functional programming is based on the lambda calculus. OCaml is in its functional parts almost pure lambda calculus, in a very practical manner: useful for many daily programming tasks. The acitve development makes improvements to the type system like generalized algebraic data types (GADT) or polymorphic variants, so when learning this language you get at once a down to earth usable compiler and advanced abstraction features.

It steers you towards a functional style, but doesn't bother you with purity and "monads everywhere" like other languages, such as Haskell.

Strong focus on *nix systems, lacking native support for MS Windows
Lacks native support for Windows systems.

OPAM is a package manager for OCaml, which is really easy to use, just like npm. It creates a .opam folder in home directory.

The documentation is great as well, and you can switch between multiple versions of OCaml for each project. You can also package your project and publish it on OPAM repositories, even if the dependencies do not exists on OPAM.

OCaml is compiled to native binary, so it's amazingly fast. Being a member of ML-family languages, it has expressive syntax for trees, and has great LLVM support.

The syntax is consistent, some syntaxic sugar but at a reasonable level, so reading code of others isn't too much confusing.

The merlin editor tool provides all you need to develop OCaml in your favourite editor.

Nim gains portability and optimization because it compiles to C, which offers a lot of choices from modern C compilers.

Readable, clean and familiar to Python developers.

Works on Windows, macOS, and Linux.