OCamlverse

Documenting everything about OCaml

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Interop with C/C++ is the most natural option for OCaml, since the runtime is partially written in C.

optint: OCaml’s built-in int is 63-bits on 64-bit platforms and 31-bits on 32-bit platforms. optint allows 64-bit platforms to use the native int type for 32-bit values, while boxing on those platforms that need it (32-bit). This is extremely useful for high-performance interop with other languages, network protocols etc.

ctypes: Modern library for binding to C libraries using pure OCaml. You should always try to bind to C code using ctypes before trying the older method.
ppx_cstubs: Possibly the easiest solution for FFI with C, allowing you to place C code in your OCaml files. Everything else is taken care of for you.
cstruct: Library to access C-style structures from OCaml. It comes with a ppx preprocessor and variants for lwt and async.
The older way of binding to C code is to create stubs in C which call functions in the OCaml runtime. This method is error prone, and you’re advised to stay away from it unless it’s absolutely necessary.
ocaml-main-program-in-c – Example build system for making mixed C/Ocaml binaries where the main program is in C.

pyml: Library for interacting with python. Uses C stubs.
pyml_bindgen: Automatically create bindings to python libraries with minimal boilerplate utilizing pyml.
OCaml-in-Python: Easily call OCaml code from Python.
Py: Library for interacting with Python 3.5 using Ctypes.
lymp: Another library for interacting with Python, this one using a Python process.

rust-ocaml-derive: provides an FFI with Rust. Works on both the OCaml-to-Rust and Rust-to-OCaml directions.
- ICFP Presentation: Safely mixing OCaml and Rust

OCaml-lua: Bindings to lua 5.1. Lua is a very efficient and light dynamic language that’s often embedded in performant applications.
OCaml-R: FFI to the R statistical language. Docs.