Ctypes is a library for binding to C libraries using pure OCaml. The
primary aim is to make writing C extensions as straightforward as
possible.

The core of ctypes is a set of combinators for describing the structure
of C types -- numeric types, arrays, pointers, structs, unions and
functions. You can use these combinators to describe the types of the
functions that you want to call, then bind directly to those functions --
all without writing or generating any C!