Convert some packages into plugins.

tests/plugins.rs

@@ -12,20 +12,42 @@ mod special_array_package {
     }
 }
 
-#[export_fn]
-fn make_greeting(n: INT) -> String {
-    format!("{} {}", n, if n > 1 { "kitties" } else { "kitty" }).into()
+macro_rules! gen_unary_functions {
+    ($op_name:ident = $op_fn:ident ( $($arg_type:ident),+ ) -> $return_type:ident) => {
+        mod $op_name { $(
+            pub mod $arg_type {
+                use super::super::*;
+
+                #[export_fn]
+                pub fn single(x: $arg_type) -> $return_type {
+                    super::super::$op_fn(x)
+                }
+            }
+        )* }
+    }
 }
 
+macro_rules! reg_functions {
+    ($mod_name:ident += $op_name:ident :: $func:ident ( $($arg_type:ident),+ )) => {
+        $(register_exported_fn!($mod_name, stringify!($op_name), $op_name::$arg_type::$func);)*
+    }
+}
+
+fn make_greeting<T: std::fmt::Display>(n: T) -> String {
+    format!("{} kitties", n)
+}
+
+gen_unary_functions!(greet = make_greeting(INT, bool, char) -> String);
+
 #[test]
 fn test_plugins_package() -> Result<(), Box<EvalAltResult>> {
     let mut engine = Engine::new();
 
-    let mut m = exported_module!(special_array_package);
-    set_exported_fn!(m, "greet", make_greeting);
-
+    let m = exported_module!(special_array_package);
     engine.load_package(m);
 
+    reg_functions!(engine += greet::single(INT, bool, char));
+
     assert_eq!(engine.eval::<INT>("let a = [1, 2, 3]; len(a, 2)")?, 6);
     assert_eq!(
         engine.eval::<String>("let a = [1, 2, 3]; greet(len(a, 2))")?,