wrote a macro to automate function registration for no-param functions

src/main.rs

@@ -16,36 +16,51 @@ extern "C" fn register_functions(_data: *mut c_void) -> *mut c_void {
     ret
 }
 
-unsafe extern "C" fn init_scm() {
+unsafe fn init_scm() {
     // this function launches the scheme process and starts bootstrapping the runtime
     // any code executed after this function but before `scm_shell()' can talk to the scheme runtime
     scm_with_guile(Some(register_functions), std::ptr::null_mut());
 }
 
-unsafe extern "C" fn run_scm(argc: c_int, argv: *mut *mut c_char) {
+unsafe fn run_scm(argc: c_int, argv: *mut *mut c_char) {
     // spawn the scheme shell, shifting execution from Rust mode to Guile mode
     scm_shell(argc, argv);
 }
 
-unsafe extern "C" fn hello_from_rust() -> SCM {
+extern "C" fn hello_from_rust() -> SCM {
     // an example function demonstrating that Rust functions work in Scheme
     println!("Hello from Rust!");
-    scm_from_int8(0)
+    unsafe {
+	scm_from_int8(0)
+    }
 }
 
+//fn register_void_function(fn_name: &[u8], f: fn() -> SCM)  {
+macro_rules! register_void_function {
+    ($x:expr, $y:expr) => {
+	// first convert the function name to a (const char *) so Guile can read it
+	let fn_name: *const c_char = CStr::from_bytes_with_nul($x).unwrap().as_ptr();
+	// convert the function into a (void *) to match with Guile's execution expectations
+	let function: *mut c_void = $y as *mut c_void;
+	// register the function as a subroutine in Guile
+	scm_c_define_gsubr(fn_name, 0, 0, 0, function);
+    }
+}
+
+
 fn main() {
     let mut ___args = std::env::args().map(|mut arg| arg.as_mut_ptr() as *mut c_char).collect::<Vec<*mut c_char>>();
     let argc = ___args.len() as c_int;
     let argv: *mut *mut c_char = ___args.as_mut_ptr();
 	    
     unsafe {
-	scm_gc_disable();
-	let hello: *mut c_void = hello_from_rust as *mut c_void;
+	// let hello: *mut c_void = hello_from_rust as *mut c_void;
 	
-	let fn_name: *const c_char = CStr::from_bytes_with_nul(b"hello-from-rust\0").unwrap().as_ptr();
+	// let fn_name: *const c_char = CStr::from_bytes_with_nul(b"hello-from-rust\0").unwrap().as_ptr();
 
 	init_scm();
-	scm_c_define_gsubr(fn_name, 0 as c_int, 0 as c_int, 0 as c_int, hello);
+	// scm_c_define_gsubr(fn_name, 0 as c_int, 0 as c_int, 0 as c_int, hello);
+	register_void_function!(b"hello-from-rust\0", hello_from_rust);
 	run_scm(argc, argv)
     };
 }