0_Guile_Rust.md

How this stuff works

This is a Guile Scheme extension written in Rust instead of C. The longer-term goal is a Rust implementation of the Rete algorithm callable from Guile.

cargo build --release
sudo mkdir -p /usr/share/guile/site/3.0/
sudo rm -rf /usr/share/guile/site/3.0/rust*
sudo cp rust-example.scm /usr/share/guile/site/3.0
sudo cp target/release/deps/libguile_rust_example.so /usr/share/guile/site

Next, type guile tryit.scm to test it out.

Cargo.toml

[package]
name = "guile-rust-example"
version = "0.1.0"
edition = "2021"

[lib]
crate-type = ["cdylib"]

[dependencies]
libc = "0.2"

lib.rs

// Put this file in a "src" subdirectory. Alas, github gists don't allow slashes in filenames, or directories.

use libc::c_char;
use std::ffi::CString;

#[no_mangle]
pub extern "C" fn rust_hello() -> *mut c_char {
    let message = "Hello from Rust!";
    let c_str = CString::new(message).unwrap();
    c_str.into_raw()
}

#[no_mangle]
pub extern "C" fn rust_add(x: i32, y: i32) -> i32 {
    x + y
}

// Free memory allocated by Rust
#[no_mangle]
pub extern "C" fn rust_free_string(ptr: *mut c_char) {
    unsafe {
        if !ptr.is_null() {
            let _ = CString::from_raw(ptr);
        }
    }
}

rust-example.scm

(define-module (rust-example)
  #:use-module (system foreign)
  #:use-module (rnrs bytevectors)
  #:export (rust-hello rust-add rust-free-string rust-string->scheme-string))

(define librust (dynamic-link "libguile_rust_example"))

(define rust-hello
  (pointer->procedure '*
                     (dynamic-func "rust_hello" librust)
                     '()))

(define rust-add
  (pointer->procedure int
                     (dynamic-func "rust_add" librust)
                     (list int int)))

(define rust-free-string
  (pointer->procedure void
                     (dynamic-func "rust_free_string" librust)
                     '(*)))

(define (rust-string->scheme-string ptr)
  (let ((str (pointer->string ptr)))
    (rust-free-string ptr)
    str))

tryit.scm

(use-modules (rust-example))
(define msg (rust-hello))
(display (rust-string->scheme-string msg))
(newline)
(display (rust-add 5 3))
(newline)