Generate a shared library and bindings for many languages.

C, python, node.js
nimble install genny


Genny - Generate Nim library bindings for many languages

So you made a cool Nim library but you want it to be available to other languages as well. With genny you can generate a dynamically linked library with a simple C API and generated bindings for many languages. In some ways its similar to SWIG project for C or djinni for C++.

Github Actions

API reference:


nimble install genny

Supported features and languages:

Language Method Enums Objects Ref Objects Seqs
Nim {.importc.}
Python ctypes
Node.js ffi-napi

Quest for "nice" language binding.

It would be easy to simply wrap the exported C api and have the user call the ugly C style methods, but that's not us. We try to generate a "nice" language api that feels like it was made custom for that language. This means where possible and target language supports it we:

  • Use naming convention that is normal of the language CamelCase, Snake_Case or Kabob-Case.
  • Make sure regular objects are passed by value and behave simply.
  • Make ref objects behave like OOP objects with members, methods and constructors.
  • Generate helper methods like == or isNull.
  • Export Seq[X] as some thing that feels like a native array.
  • Export Seq[X] on a ref object behaves like what we call a bound-seq.
  • Support the [] syntax.
  • Support the . member syntax.
  • Overload math operators +, -, *, /.
  • Overload procs, where we first unpack them to different C calls with unique prefixes and them repack them back into overloaded methods or functions.
  • Pass optional arguments.
  • Pass enums and constants.
  • Synchronize native GC and Nim's ARC GC.
  • And even copy the comments so that automated tools can use them.

A bindings interface DSL

We provide a DSL that you can use to define how things need to be exported. The DSL is pretty simple to follow:

import genny, pixie




exportObject Matrix3:
    mul(Matrix3, Matrix3)

exportRefObject Mask:
    newMask(int, int)
    writeFile(Mask, string)

# Must have this at the end.
writeFiles("bindings/generated", "pixie")
include generated/internal

See more in the pixie bindings

Genny is experimental and opinionated

Genny generates a dynamic library C API for your Nim library and generates bindings for that dynamic library in many languages. To do this, things like proc overloads, complex types, sequences, and many other Nim features need to be addressed to make them work over a C interface.

To make that C interface, Genny makes assumptions about what your Nim source looks like and how to give overloaded procedures unique names. This may not work out of the box for every Nim library yet!

Example uses

This version of Genny was created to generate bindings for Pixie. You can see how Pixie's dynamic library API is exported and the bindings generated in this file and the results here.

Nim is great, why other languages?

Nim is a niche language, we feel we can broaden Nim's appeal by creating Nim libraries for other more popular language and have Nim slowly work into other companies. Maybe after companies see that they already use Nim, they can start writing their own code in it.

Why add Nim binding support for a Nim library?

"Can't you just import your cool library in Nim?" We though it was important to test the library in a what we call Nim-C-Nim sandwich. It makes sure everyone uses your library API the same way. This also means you could ship huge Nim libraries as DLLs and use them in your Nim programs without recompiling everything every time.