gs0510 / ocaml-interop

OCaml<->Rust FFI with an emphasis on safety.

ocaml-interop

Zinc-iron alloy coating is used in parts that need very good corrosion protection.

API IS CONSIDERED UNSTABLE AT THE MOMENT AND IS LIKELY TO CHANGE IN THE FUTURE

ocaml-interop is an OCaml<->Rust FFI with an emphasis on safety inspired by caml-oxide and ocaml-rs.

Read the full documentation here.

Report issues on Github.

Table of Contents

• How does it work
• A quick taste
• References and links

How does it work

ocaml-interop, just like caml-oxide, encodes the invariants of OCaml's garbage collector into the rules of Rust's borrow checker. Any violation of these invariants results in a compilation error produced by Rust's borrow checker.

A quick taste

Convert between plain OCaml and Rust values

let rust_string = ocaml_string.to_rust();
// `cr` = OCaml runtime handle
let new_ocaml_string = to_ocaml!(cr, rust_string);

Convert between Rust and OCaml structs/records

(* OCaml *)
type my_record = {
  string_field: string;
  tuple_field: (string * int);
}

// Rust
struct MyStruct {
    string_field: String,
    tuple_field: (String, i64),
}

impl_conv_ocaml_record! {
    MyStruct {
        string_field: String,
        tuple_field: (String, i64),
    }
}

// ...

let rust_struct = ocaml_record.to_rust();
let new_ocaml_record = to_ocaml!(cr, rust_struct);

Convert between OCaml and Rust variants/enums

(* OCaml *)
type my_variant =
  | EmptyTag
  | TagWithInt of int

// Rust
enum MyEnum {
    EmptyTag,
    TagWithInt(i64),
}

impl_conv_ocaml_variant! {
    MyEnum {
        EmptyTag,
        TagWithInt(OCamlInt),
    }
}

// ...

let rust_enum = ocaml_variant.to_rust();
let new_ocaml_variant = to_ocaml!(cr, rust_enum);

Call OCaml functions from Rust

(* OCaml *)
Callback.register "ocaml_print_endline" print_endline

ocaml! {
    fn ocaml_print_endline(s: String);
}

// ...

let ocaml_string = to_ocaml!(cr, "hello OCaml!", root_var);
ocaml_print_endline(cr, ocaml_string);

Call Rust functions from OCaml

// Rust
ocaml_export! {
    pub fn twice_boxed_int(cr, num: OCaml<OCamlInt64>) -> OCaml<OCamlInt64> {
        let num = num.to_rust();
        let result = num * 2;
        to_ocaml!(cf, result)
    }
}

(* OCaml *)
external rust_twice_boxed_int: int64 -> int64 = "twice_boxed_int"

(* ... *)

let result = rust_twice_boxed_int 123L in
(* ... *)

References and links

• OCaml Manual: Chapter 20 Interfacing C with OCaml.
• Safely Mixing OCaml and Rust paper by Stephen Dolan.
• Safely Mixing OCaml and Rust talk by Stephen Dolan.
• CAMLroot: revisiting the OCaml FFI.
• caml-oxide, the code from that paper.
• ocaml-rs, another OCaml<->Rust FFI library.