diff --git a/RELEASES.md b/RELEASES.md
index 3dcca24e..e0dc9f06 100644
--- a/RELEASES.md
+++ b/RELEASES.md
@@ -22,7 +22,7 @@ Breaking changes
 ----------------
 
 * `Module::set_fn`, `Module::set_raw_fn` and `Module::set_fn_XXX_mut` all take an additional parameter of `FnNamespace`.
-* `Module::set_fn` takes a further parameter with a list of parameter names and types, if any.
+* `Module::set_fn` takes a further parameter with a list of parameter names/types plus the function return type, if any.
 * `Module::get_sub_module_mut` is removed.
 * `begin`, `end`, `unless` are now reserved keywords.
 * `EvalPackage` is removed in favor of `Engine::disable_symbol`.
@@ -37,7 +37,7 @@ New features
 * New `set_exported_global_fn!` macro to register a plugin function and expose it to the global namespace.
 * `Module::set_fn_XXX_mut` can expose a module function to the global namespace. This is convenient when registering an API for a custom type.
 * `Module::set_getter_fn`, `Module::set_setter_fn`, `Module::set_indexer_get_fn`, `Module::set_indexer_set_fn` all expose the function to the global namespace by default. This is convenient when registering an API for a custom type.
-* New `Module::update_fn_param_names` to update a module function's parameter names and types.
+* New `Module::update_fn_metadata` to update a module function's parameter names and types.
 * New `#[rhai_fn(global)]` and `#[rhai_fn(internal)]` attributes to determine whether a function defined in a plugin module should be exposed to the global namespace. This is convenient when defining an API for a custom type.
 
 Enhancements
diff --git a/codegen/src/function.rs b/codegen/src/function.rs
index 5f976fd9..e84232c3 100644
--- a/codegen/src/function.rs
+++ b/codegen/src/function.rs
@@ -84,7 +84,15 @@ pub(crate) fn flatten_type_groups(ty: &syn::Type) -> &syn::Type {
 }
 
 pub(crate) fn print_type(ty: &syn::Type) -> String {
-    ty.to_token_stream().to_string().replace("& ", "&")
+    ty.to_token_stream()
+        .to_string()
+        .replace(" , ", ", ")
+        .replace("& ", "&")
+        .replace(" :: ", "::")
+        .replace(" ( ", "(")
+        .replace(" ) ", ")")
+        .replace(" < ", "<")
+        .replace(" > ", ">")
 }
 
 #[derive(Debug, Default)]
@@ -582,6 +590,7 @@ impl ExportedFn {
         let callable_block = self.generate_callable("Token");
         let input_names_block = self.generate_input_names("Token");
         let input_types_block = self.generate_input_types("Token");
+        let return_type_block = self.generate_return_type("Token");
         let dyn_result_fn_block = self.generate_dynamic_fn();
         quote! {
             #[allow(unused)]
@@ -592,6 +601,7 @@ impl ExportedFn {
                 #callable_block
                 #input_names_block
                 #input_types_block
+                #return_type_block
                 #dyn_result_fn_block
             }
         }
@@ -687,6 +697,19 @@ impl ExportedFn {
         }
     }
 
+    pub fn generate_return_type(&self, on_type_name: &str) -> proc_macro2::TokenStream {
+        let token_name: syn::Ident = syn::Ident::new(on_type_name, self.name().span());
+        let return_type_fn_name: syn::Ident = syn::Ident::new(
+            format!("{}_return_type", on_type_name.to_lowercase()).as_str(),
+            self.name().span(),
+        );
+        quote! {
+            pub fn #return_type_fn_name() -> &'static str {
+                #token_name().return_type()
+            }
+        }
+    }
+
     pub fn generate_impl(&self, on_type_name: &str) -> proc_macro2::TokenStream {
         let sig_name = self.name().clone();
         let name = self.params.name.as_ref().map_or_else(
@@ -701,6 +724,12 @@ impl ExportedFn {
         let mut unpack_exprs: Vec<syn::Expr> = Vec::new();
         let mut input_type_names: Vec<String> = Vec::new();
         let mut input_type_exprs: Vec<syn::Expr> = Vec::new();
+
+        let return_type = self
+            .return_type()
+            .map(print_type)
+            .unwrap_or_else(|| "()".to_string());
+
         let skip_first_arg;
 
         if self.pass_context {
@@ -867,6 +896,9 @@ impl ExportedFn {
                 fn input_types(&self) -> Box<[TypeId]> {
                     new_vec![#(#input_type_exprs),*].into_boxed_slice()
                 }
+                fn return_type(&self) -> &'static str {
+                    #return_type
+                }
             }
         }
     }
diff --git a/codegen/src/rhai_module.rs b/codegen/src/rhai_module.rs
index 129089b0..caef2ba2 100644
--- a/codegen/src/rhai_module.rs
+++ b/codegen/src/rhai_module.rs
@@ -136,6 +136,11 @@ pub(crate) fn generate_body(
             })
             .collect();
 
+        let return_type = function
+            .return_type()
+            .map(print_type)
+            .unwrap_or_else(|| "()".to_string());
+
         if let Some(ns) = function.params().namespace {
             namespace = ns;
         }
@@ -151,7 +156,7 @@ pub(crate) fn generate_body(
             set_fn_stmts.push(
                 syn::parse2::<syn::Stmt>(quote! {
                     m.set_fn(#fn_literal, FnNamespace::#ns_str, FnAccess::Public,
-                                Some(&[#(#fn_input_names),*]), &[#(#fn_input_types),*],
+                                Some(&[#(#fn_input_names,)* #return_type]), &[#(#fn_input_types),*],
                                 #fn_token_name().into());
                 })
                 .unwrap(),
@@ -166,6 +171,7 @@ pub(crate) fn generate_body(
         gen_fn_tokens.push(function.generate_callable(&fn_token_name.to_string()));
         gen_fn_tokens.push(function.generate_input_names(&fn_token_name.to_string()));
         gen_fn_tokens.push(function.generate_input_types(&fn_token_name.to_string()));
+        gen_fn_tokens.push(function.generate_return_type(&fn_token_name.to_string()));
     }
 
     let mut generate_fncall = syn::parse2::<syn::ItemMod>(quote! {
diff --git a/codegen/src/test/function.rs b/codegen/src/test/function.rs
index c0e74229..7a750123 100644
--- a/codegen/src/test/function.rs
+++ b/codegen/src/test/function.rs
@@ -292,6 +292,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn token_callable() -> CallableFunction {
                     Token().into()
@@ -302,6 +305,9 @@ mod generate_tests {
                 pub fn token_input_types() -> Box<[TypeId]> {
                     Token().input_types()
                 }
+                pub fn token_return_type() -> &'static str {
+                    Token().return_type()
+                }
                 pub fn dynamic_result_fn() -> Result<Dynamic, Box<EvalAltResult> > {
                     Ok(Dynamic::from(do_nothing()))
                 }
@@ -340,6 +346,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<usize>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn token_callable() -> CallableFunction {
                     Token().into()
@@ -350,6 +359,9 @@ mod generate_tests {
                 pub fn token_input_types() -> Box<[TypeId]> {
                     Token().input_types()
                 }
+                pub fn token_return_type() -> &'static str {
+                    Token().return_type()
+                }
                 pub fn dynamic_result_fn(x: usize) -> Result<Dynamic, Box<EvalAltResult> > {
                     Ok(Dynamic::from(do_something(x)))
                 }
@@ -388,6 +400,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<usize>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn token_callable() -> CallableFunction {
                     Token().into()
@@ -398,6 +413,9 @@ mod generate_tests {
                 pub fn token_input_types() -> Box<[TypeId]> {
                     Token().input_types()
                 }
+                pub fn token_return_type() -> &'static str {
+                    Token().return_type()
+                }
                 pub fn dynamic_result_fn(context: NativeCallContext, x: usize) -> Result<Dynamic, Box<EvalAltResult> > {
                     Ok(Dynamic::from(do_something(context, x)))
                 }
@@ -438,6 +456,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "rhai::Dynamic"
+                    }
                 }
                 pub fn token_callable() -> CallableFunction {
                     Token().into()
@@ -448,6 +469,9 @@ mod generate_tests {
                 pub fn token_input_types() -> Box<[TypeId]> {
                     Token().input_types()
                 }
+                pub fn token_return_type() -> &'static str {
+                    Token().return_type()
+                }
                 pub fn dynamic_result_fn() -> Result<Dynamic, Box<EvalAltResult> > {
                     Ok(return_dynamic())
                 }
@@ -482,7 +506,10 @@ mod generate_tests {
                 fn input_types(&self) -> Box<[TypeId]> {
                     new_vec![TypeId::of::<usize>()].into_boxed_slice()
                 }
-            }
+                fn return_type(&self) -> &'static str {
+                    "()"
+                }
+        }
         };
 
         let item_fn = syn::parse2::<ExportedFn>(input_tokens).unwrap();
@@ -519,6 +546,9 @@ mod generate_tests {
                         new_vec![TypeId::of::<usize>(),
                              TypeId::of::<usize>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "usize"
+                    }
                 }
                 pub fn token_callable() -> CallableFunction {
                     Token().into()
@@ -529,6 +559,9 @@ mod generate_tests {
                 pub fn token_input_types() -> Box<[TypeId]> {
                     Token().input_types()
                 }
+                pub fn token_return_type() -> &'static str {
+                    Token().return_type()
+                }
                 pub fn dynamic_result_fn(x: usize, y: usize) -> Result<Dynamic, Box<EvalAltResult> > {
                     Ok(Dynamic::from(add_together(x, y)))
                 }
@@ -569,6 +602,9 @@ mod generate_tests {
                         new_vec![TypeId::of::<usize>(),
                              TypeId::of::<usize>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn token_callable() -> CallableFunction {
                     Token().into()
@@ -579,6 +615,9 @@ mod generate_tests {
                 pub fn token_input_types() -> Box<[TypeId]> {
                     Token().input_types()
                 }
+                pub fn token_return_type() -> &'static str {
+                    Token().return_type()
+                }
                 pub fn dynamic_result_fn(x: &mut usize, y: usize) -> Result<Dynamic, Box<EvalAltResult> > {
                     Ok(Dynamic::from(increment(x, y)))
                 }
@@ -618,6 +657,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<ImmutableString>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn token_callable() -> CallableFunction {
                     Token().into()
@@ -628,6 +670,9 @@ mod generate_tests {
                 pub fn token_input_types() -> Box<[TypeId]> {
                     Token().input_types()
                 }
+                pub fn token_return_type() -> &'static str {
+                    Token().return_type()
+                }
                 pub fn dynamic_result_fn(message: &str) -> Result<Dynamic, Box<EvalAltResult> > {
                     Ok(Dynamic::from(special_print(message)))
                 }
diff --git a/codegen/src/test/module.rs b/codegen/src/test/module.rs
index 8afdf134..8c6bdd50 100644
--- a/codegen/src/test/module.rs
+++ b/codegen/src/test/module.rs
@@ -297,7 +297,7 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("get_mystic_number", FnNamespace::Internal, FnAccess::Public, Some(&[]), &[],
+                    m.set_fn("get_mystic_number", FnNamespace::Internal, FnAccess::Public, Some(&["INT"]), &[],
                              get_mystic_number_token().into());
                     if flatten {} else {}
                 }
@@ -321,6 +321,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "INT"
+                    }
                 }
                 pub fn get_mystic_number_token_callable() -> CallableFunction {
                     get_mystic_number_token().into()
@@ -331,6 +334,9 @@ mod generate_tests {
                 pub fn get_mystic_number_token_input_types() -> Box<[TypeId]> {
                     get_mystic_number_token().input_types()
                 }
+                pub fn get_mystic_number_token_return_type() -> &'static str {
+                    get_mystic_number_token().return_type()
+                }
             }
         };
 
@@ -365,7 +371,7 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add_one_to", FnNamespace::Global, FnAccess::Public, Some(&["x: INT"]), &[core::any::TypeId::of::<INT>()],
+                    m.set_fn("add_one_to", FnNamespace::Global, FnAccess::Public, Some(&["x: INT", "INT"]), &[core::any::TypeId::of::<INT>()],
                              add_one_to_token().into());
                     if flatten {} else {}
                 }
@@ -390,6 +396,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<INT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "INT"
+                    }
                 }
                 pub fn add_one_to_token_callable() -> CallableFunction {
                     add_one_to_token().into()
@@ -400,6 +409,9 @@ mod generate_tests {
                 pub fn add_one_to_token_input_types() -> Box<[TypeId]> {
                     add_one_to_token().input_types()
                 }
+                pub fn add_one_to_token_return_type() -> &'static str {
+                    add_one_to_token().return_type()
+                }
             }
         };
 
@@ -433,7 +445,7 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add_one_to", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT"]), &[core::any::TypeId::of::<INT>()],
+                    m.set_fn("add_one_to", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "INT"]), &[core::any::TypeId::of::<INT>()],
                              add_one_to_token().into());
                     if flatten {} else {}
                 }
@@ -458,6 +470,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<INT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "INT"
+                    }
                 }
                 pub fn add_one_to_token_callable() -> CallableFunction {
                     add_one_to_token().into()
@@ -468,6 +483,9 @@ mod generate_tests {
                 pub fn add_one_to_token_input_types() -> Box<[TypeId]> {
                     add_one_to_token().input_types()
                 }
+                pub fn add_one_to_token_return_type() -> &'static str {
+                    add_one_to_token().return_type()
+                }
             }
         };
 
@@ -512,9 +530,9 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add_n", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT"]), &[core::any::TypeId::of::<INT>()],
+                    m.set_fn("add_n", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "INT"]), &[core::any::TypeId::of::<INT>()],
                              add_one_to_token().into());
-                    m.set_fn("add_n", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT"]),
+                    m.set_fn("add_n", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT", "INT"]),
                              &[core::any::TypeId::of::<INT>(), core::any::TypeId::of::<INT>()],
                              add_n_to_token().into());
                     if flatten {} else {}
@@ -540,6 +558,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<INT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "INT"
+                    }
                 }
                 pub fn add_one_to_token_callable() -> CallableFunction {
                     add_one_to_token().into()
@@ -550,6 +571,9 @@ mod generate_tests {
                 pub fn add_one_to_token_input_types() -> Box<[TypeId]> {
                     add_one_to_token().input_types()
                 }
+                pub fn add_one_to_token_return_type() -> &'static str {
+                    add_one_to_token().return_type()
+                }
 
                 #[allow(non_camel_case_types)]
                 struct add_n_to_token();
@@ -574,6 +598,9 @@ mod generate_tests {
                         new_vec![TypeId::of::<INT>(),
                                  TypeId::of::<INT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "INT"
+                    }
                 }
                 pub fn add_n_to_token_callable() -> CallableFunction {
                     add_n_to_token().into()
@@ -584,6 +611,9 @@ mod generate_tests {
                 pub fn add_n_to_token_input_types() -> Box<[TypeId]> {
                     add_n_to_token().input_types()
                 }
+                pub fn add_n_to_token_return_type() -> &'static str {
+                    add_n_to_token().return_type()
+                }
             }
         };
 
@@ -617,7 +647,7 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add_together", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT"]),
+                    m.set_fn("add_together", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT", "INT"]),
                              &[core::any::TypeId::of::<INT>(), core::any::TypeId::of::<INT>()],
                              add_together_token().into());
                     if flatten {} else {}
@@ -645,6 +675,9 @@ mod generate_tests {
                         new_vec![TypeId::of::<INT>(),
                              TypeId::of::<INT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "INT"
+                    }
                 }
                 pub fn add_together_token_callable() -> CallableFunction {
                     add_together_token().into()
@@ -655,6 +688,9 @@ mod generate_tests {
                 pub fn add_together_token_input_types() -> Box<[TypeId]> {
                     add_together_token().input_types()
                 }
+                pub fn add_together_token_return_type() -> &'static str {
+                    add_together_token().return_type()
+                }
             }
         };
 
@@ -689,13 +725,13 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("add", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT"]),
+                    m.set_fn("add", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT", "INT"]),
                              &[core::any::TypeId::of::<INT>(), core::any::TypeId::of::<INT>()],
                              add_together_token().into());
-                    m.set_fn("+", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT"]),
+                    m.set_fn("+", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT", "INT"]),
                              &[core::any::TypeId::of::<INT>(), core::any::TypeId::of::<INT>()],
                              add_together_token().into());
-                    m.set_fn("add_together", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT"]),
+                    m.set_fn("add_together", FnNamespace::Internal, FnAccess::Public, Some(&["x: INT", "y: INT", "INT"]),
                              &[core::any::TypeId::of::<INT>(), core::any::TypeId::of::<INT>()],
                              add_together_token().into());
                     if flatten {} else {}
@@ -723,6 +759,9 @@ mod generate_tests {
                         new_vec![TypeId::of::<INT>(),
                              TypeId::of::<INT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "INT"
+                    }
                 }
                 pub fn add_together_token_callable() -> CallableFunction {
                     add_together_token().into()
@@ -733,6 +772,9 @@ mod generate_tests {
                 pub fn add_together_token_input_types() -> Box<[TypeId]> {
                     add_together_token().input_types()
                 }
+                pub fn add_together_token_return_type() -> &'static str {
+                    add_together_token().return_type()
+                }
             }
         };
 
@@ -948,7 +990,7 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("get_mystic_number", FnNamespace::Internal, FnAccess::Public, Some(&[]), &[],
+                    m.set_fn("get_mystic_number", FnNamespace::Internal, FnAccess::Public, Some(&["INT"]), &[],
                              get_mystic_number_token().into());
                     if flatten {} else {}
                 }
@@ -972,6 +1014,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "INT"
+                    }
                 }
                 pub fn get_mystic_number_token_callable() -> CallableFunction {
                     get_mystic_number_token().into()
@@ -982,6 +1027,9 @@ mod generate_tests {
                 pub fn get_mystic_number_token_input_types() -> Box<[TypeId]> {
                     get_mystic_number_token().input_types()
                 }
+                pub fn get_mystic_number_token_return_type() -> &'static str {
+                    get_mystic_number_token().return_type()
+                }
             }
         };
 
@@ -1047,7 +1095,7 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                     m.set_fn("print_out_to", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: &str"]), &[core::any::TypeId::of::<ImmutableString>()],
+                             Some(&["x: &str", "()"]), &[core::any::TypeId::of::<ImmutableString>()],
                              print_out_to_token().into());
                     if flatten {} else {}
                 }
@@ -1072,6 +1120,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<ImmutableString>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn print_out_to_token_callable() -> CallableFunction {
                     print_out_to_token().into()
@@ -1082,6 +1133,9 @@ mod generate_tests {
                 pub fn print_out_to_token_input_types() -> Box<[TypeId]> {
                     print_out_to_token().input_types()
                 }
+                pub fn print_out_to_token_return_type() -> &'static str {
+                    print_out_to_token().return_type()
+                }
             }
         };
 
@@ -1116,7 +1170,7 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                     m.set_fn("print_out_to", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: String"]), &[core::any::TypeId::of::<ImmutableString>()],
+                             Some(&["x: String", "()"]), &[core::any::TypeId::of::<ImmutableString>()],
                              print_out_to_token().into());
                     if flatten {} else {}
                 }
@@ -1141,6 +1195,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<ImmutableString>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn print_out_to_token_callable() -> CallableFunction {
                     print_out_to_token().into()
@@ -1151,6 +1208,9 @@ mod generate_tests {
                 pub fn print_out_to_token_input_types() -> Box<[TypeId]> {
                     print_out_to_token().input_types()
                 }
+                pub fn print_out_to_token_return_type() -> &'static str {
+                    print_out_to_token().return_type()
+                }
             }
         };
 
@@ -1185,7 +1245,7 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                     m.set_fn("increment", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: &mut FLOAT"]), &[core::any::TypeId::of::<FLOAT>()],
+                             Some(&["x: &mut FLOAT", "()"]), &[core::any::TypeId::of::<FLOAT>()],
                              increment_token().into());
                     if flatten {} else {}
                 }
@@ -1210,6 +1270,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<FLOAT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn increment_token_callable() -> CallableFunction {
                     increment_token().into()
@@ -1220,6 +1283,9 @@ mod generate_tests {
                 pub fn increment_token_input_types() -> Box<[TypeId]> {
                     increment_token().input_types()
                 }
+                pub fn increment_token_return_type() -> &'static str {
+                    increment_token().return_type()
+                }
             }
         };
 
@@ -1257,7 +1323,7 @@ mod generate_tests {
                     #[allow(unused_mut)]
                     pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                         m.set_fn("increment", FnNamespace::Internal, FnAccess::Public,
-                                 Some(&["x: &mut FLOAT"]), &[core::any::TypeId::of::<FLOAT>()],
+                                 Some(&["x: &mut FLOAT", "()"]), &[core::any::TypeId::of::<FLOAT>()],
                                  increment_token().into());
                         if flatten {} else {}
                     }
@@ -1282,6 +1348,9 @@ mod generate_tests {
                         fn input_types(&self) -> Box<[TypeId]> {
                             new_vec![TypeId::of::<FLOAT>()].into_boxed_slice()
                         }
+                        fn return_type(&self) -> &'static str {
+                            "()"
+                        }
                     }
                     pub fn increment_token_callable() -> CallableFunction {
                         increment_token().into()
@@ -1292,6 +1361,9 @@ mod generate_tests {
                     pub fn increment_token_input_types() -> Box<[TypeId]> {
                         increment_token().input_types()
                     }
+                    pub fn increment_token_return_type() -> &'static str {
+                        increment_token().return_type()
+                    }
                 }
                 #[allow(unused_imports)]
                 use super::*;
@@ -1350,7 +1422,7 @@ mod generate_tests {
                     #[allow(unused_mut)]
                     pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                         m.set_fn("increment", FnNamespace::Internal, FnAccess::Public,
-                                 Some(&["x: &mut FLOAT"]), &[core::any::TypeId::of::<FLOAT>()],
+                                 Some(&["x: &mut FLOAT", "()"]), &[core::any::TypeId::of::<FLOAT>()],
                                  increment_token().into());
                         if flatten {} else {}
                     }
@@ -1375,6 +1447,9 @@ mod generate_tests {
                         fn input_types(&self) -> Box<[TypeId]> {
                             new_vec![TypeId::of::<FLOAT>()].into_boxed_slice()
                         }
+                        fn return_type(&self) -> &'static str {
+                            "()"
+                        }
                     }
                     pub fn increment_token_callable() -> CallableFunction {
                         increment_token().into()
@@ -1385,6 +1460,9 @@ mod generate_tests {
                     pub fn increment_token_input_types() -> Box<[TypeId]> {
                         increment_token().input_types()
                     }
+                    pub fn increment_token_return_type() -> &'static str {
+                        increment_token().return_type()
+                    }
                 }
                 #[allow(unused_imports)]
                 use super::*;
@@ -1441,7 +1519,8 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("get$square", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64"]), &[core::any::TypeId::of::<u64>()],
+                    m.set_fn("get$square", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "u64"]),
+                             &[core::any::TypeId::of::<u64>()],
                              int_foo_token().into());
                     if flatten {} else {}
                 }
@@ -1466,6 +1545,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<u64>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "u64"
+                    }
                 }
                 pub fn int_foo_token_callable() -> CallableFunction {
                     int_foo_token().into()
@@ -1476,6 +1558,9 @@ mod generate_tests {
                 pub fn int_foo_token_input_types() -> Box<[TypeId]> {
                     int_foo_token().input_types()
                 }
+                pub fn int_foo_token_return_type() -> &'static str {
+                    int_foo_token().return_type()
+                }
             }
         };
 
@@ -1510,9 +1595,9 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("square", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64"]), &[core::any::TypeId::of::<u64>()],
+                    m.set_fn("square", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "u64"]), &[core::any::TypeId::of::<u64>()],
                              int_foo_token().into());
-                    m.set_fn("get$square", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64"]), &[core::any::TypeId::of::<u64>()],
+                    m.set_fn("get$square", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "u64"]), &[core::any::TypeId::of::<u64>()],
                              int_foo_token().into());
                     if flatten {} else {}
                 }
@@ -1537,6 +1622,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<u64>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "u64"
+                    }
                 }
                 pub fn int_foo_token_callable() -> CallableFunction {
                     int_foo_token().into()
@@ -1547,6 +1635,9 @@ mod generate_tests {
                 pub fn int_foo_token_input_types() -> Box<[TypeId]> {
                     int_foo_token().input_types()
                 }
+                pub fn int_foo_token_return_type() -> &'static str {
+                    int_foo_token().return_type()
+                }
             }
         };
 
@@ -1581,7 +1672,7 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("set$squared", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "y: u64"]),
+                    m.set_fn("set$squared", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "y: u64", "()"]),
                              &[core::any::TypeId::of::<u64>(), core::any::TypeId::of::<u64>()],
                              int_foo_token().into());
                     if flatten {} else {}
@@ -1608,6 +1699,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<u64>(), TypeId::of::<u64>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn int_foo_token_callable() -> CallableFunction {
                     int_foo_token().into()
@@ -1618,6 +1712,9 @@ mod generate_tests {
                 pub fn int_foo_token_input_types() -> Box<[TypeId]> {
                     int_foo_token().input_types()
                 }
+                pub fn int_foo_token_return_type() -> &'static str {
+                    int_foo_token().return_type()
+                }
             }
         };
 
@@ -1652,10 +1749,10 @@ mod generate_tests {
                 }
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
-                    m.set_fn("set_sq", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "y: u64"]),
+                    m.set_fn("set_sq", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "y: u64", "()"]),
                              &[core::any::TypeId::of::<u64>(), core::any::TypeId::of::<u64>()],
                              int_foo_token().into());
-                    m.set_fn("set$squared", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "y: u64"]),
+                    m.set_fn("set$squared", FnNamespace::Internal, FnAccess::Public, Some(&["x: &mut u64", "y: u64", "()"]),
                              &[core::any::TypeId::of::<u64>(), core::any::TypeId::of::<u64>()],
                              int_foo_token().into());
                     if flatten {} else {}
@@ -1682,6 +1779,9 @@ mod generate_tests {
                     fn input_types(&self) -> Box<[TypeId]> {
                         new_vec![TypeId::of::<u64>(), TypeId::of::<u64>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn int_foo_token_callable() -> CallableFunction {
                     int_foo_token().into()
@@ -1692,6 +1792,9 @@ mod generate_tests {
                 pub fn int_foo_token_input_types() -> Box<[TypeId]> {
                     int_foo_token().input_types()
                 }
+                pub fn int_foo_token_return_type() -> &'static str {
+                    int_foo_token().return_type()
+                }
             }
         };
 
@@ -1727,7 +1830,7 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                     m.set_fn("index$get$", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: &mut MyCollection", "i: u64"]),
+                             Some(&["x: &mut MyCollection", "i: u64", "FLOAT"]),
                              &[core::any::TypeId::of::<MyCollection>(),
                                core::any::TypeId::of::<u64>()],
                              get_by_index_token().into());
@@ -1756,6 +1859,9 @@ mod generate_tests {
                         new_vec![TypeId::of::<MyCollection>(),
                                  TypeId::of::<u64>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "FLOAT"
+                    }
                 }
                 pub fn get_by_index_token_callable() -> CallableFunction {
                     get_by_index_token().into()
@@ -1766,6 +1872,9 @@ mod generate_tests {
                 pub fn get_by_index_token_input_types() -> Box<[TypeId]> {
                     get_by_index_token().input_types()
                 }
+                pub fn get_by_index_token_return_type() -> &'static str {
+                    get_by_index_token().return_type()
+                }
             }
         };
 
@@ -1801,12 +1910,12 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                     m.set_fn("get", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: &mut MyCollection", "i: u64"]),
+                             Some(&["x: &mut MyCollection", "i: u64", "FLOAT"]),
                              &[core::any::TypeId::of::<MyCollection>(),
                                core::any::TypeId::of::<u64>()],
                              get_by_index_token().into());
                     m.set_fn("index$get$", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: &mut MyCollection", "i: u64"]),
+                             Some(&["x: &mut MyCollection", "i: u64", "FLOAT"]),
                              &[core::any::TypeId::of::<MyCollection>(),
                                core::any::TypeId::of::<u64>()],
                              get_by_index_token().into());
@@ -1835,6 +1944,9 @@ mod generate_tests {
                         new_vec![TypeId::of::<MyCollection>(),
                                  TypeId::of::<u64>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "FLOAT"
+                    }
                 }
                 pub fn get_by_index_token_callable() -> CallableFunction {
                     get_by_index_token().into()
@@ -1845,6 +1957,9 @@ mod generate_tests {
                 pub fn get_by_index_token_input_types() -> Box<[TypeId]> {
                     get_by_index_token().input_types()
                 }
+                pub fn get_by_index_token_return_type() -> &'static str {
+                    get_by_index_token().return_type()
+                }
             }
         };
 
@@ -1880,7 +1995,7 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                     m.set_fn("index$set$", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: &mut MyCollection", "i: u64", "item: FLOAT"]),
+                             Some(&["x: &mut MyCollection", "i: u64", "item: FLOAT", "()"]),
                              &[core::any::TypeId::of::<MyCollection>(),
                                core::any::TypeId::of::<u64>(),
                                core::any::TypeId::of::<FLOAT>()],
@@ -1912,6 +2027,9 @@ mod generate_tests {
                                  TypeId::of::<u64>(),
                                  TypeId::of::<FLOAT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn set_by_index_token_callable() -> CallableFunction {
                     set_by_index_token().into()
@@ -1922,6 +2040,9 @@ mod generate_tests {
                 pub fn set_by_index_token_input_types() -> Box<[TypeId]> {
                     set_by_index_token().input_types()
                 }
+                pub fn set_by_index_token_return_type() -> &'static str {
+                    set_by_index_token().return_type()
+                }
             }
         };
 
@@ -1957,13 +2078,13 @@ mod generate_tests {
                 #[allow(unused_mut)]
                 pub fn rhai_generate_into_module(m: &mut Module, flatten: bool) {
                     m.set_fn("set", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: &mut MyCollection", "i: u64", "item: FLOAT"]),
+                             Some(&["x: &mut MyCollection", "i: u64", "item: FLOAT", "()"]),
                              &[core::any::TypeId::of::<MyCollection>(),
                                core::any::TypeId::of::<u64>(),
                                core::any::TypeId::of::<FLOAT>()],
                              set_by_index_token().into());
                     m.set_fn("index$set$", FnNamespace::Internal, FnAccess::Public,
-                             Some(&["x: &mut MyCollection", "i: u64", "item: FLOAT"]),
+                             Some(&["x: &mut MyCollection", "i: u64", "item: FLOAT", "()"]),
                              &[core::any::TypeId::of::<MyCollection>(),
                                core::any::TypeId::of::<u64>(),
                                core::any::TypeId::of::<FLOAT>()],
@@ -1995,6 +2116,9 @@ mod generate_tests {
                                  TypeId::of::<u64>(),
                                  TypeId::of::<FLOAT>()].into_boxed_slice()
                     }
+                    fn return_type(&self) -> &'static str {
+                        "()"
+                    }
                 }
                 pub fn set_by_index_token_callable() -> CallableFunction {
                     set_by_index_token().into()
@@ -2005,6 +2129,9 @@ mod generate_tests {
                 pub fn set_by_index_token_input_types() -> Box<[TypeId]> {
                     set_by_index_token().input_types()
                 }
+                pub fn set_by_index_token_return_type() -> &'static str {
+                    set_by_index_token().return_type()
+                }
             }
         };
 
diff --git a/doc/src/rust/modules/create.md b/doc/src/rust/modules/create.md
index 937f85e9..6e1a1479 100644
--- a/doc/src/rust/modules/create.md
+++ b/doc/src/rust/modules/create.md
@@ -32,7 +32,13 @@ a module's functionalities to Rhai.
 use rhai::{Engine, Module};
 
 let mut module = Module::new();             // new module
-module.set_fn_1("inc", |x: i64| Ok(x+1));   // use the 'set_fn_XXX' API to add functions
+
+// Use the 'set_fn_XXX' API to add functions.
+let hash = module.set_fn_1("inc", |x: i64| Ok(x+1));
+
+// Remember to update the parameter names/types and return type metadata.
+// 'set_fn_XXX' by default does not set function metadata.
+module.update_fn_metadata(hash, ["x: i64", "i64"]);
 
 // Load the module into the Engine as a new package.
 let mut engine = Engine::new();
@@ -51,7 +57,13 @@ Make the `Module` a Global Module
 use rhai::{Engine, Module};
 
 let mut module = Module::new();             // new module
-module.set_fn_1("inc", |x: i64| Ok(x+1));   // use the 'set_fn_XXX' API to add functions
+
+// Use the 'set_fn_XXX' API to add functions.
+let hash = module.set_fn_1("inc", |x: i64| Ok(x+1));
+
+// Remember to update the parameter names/types and return type metadata.
+// 'set_fn_XXX' by default does not set function metadata.
+module.update_fn_metadata(hash, ["x: i64", "i64"]);
 
 // Load the module into the Engine as a sub-module named 'calc'
 let mut engine = Engine::new();
@@ -71,9 +83,11 @@ use rhai::{Engine, Module, FnNamespace};
 let mut module = Module::new();             // new module
 
 // Expose method 'inc' to the global namespace (default is 'Internal')
-module.set_fn_1_mut("inc", FnNamespace::Global,
-    |x: &mut i64| Ok(x+1)
-);
+let hash = module.set_fn_1_mut("inc", FnNamespace::Global, |x: &mut i64| Ok(x+1));
+
+// Remember to update the parameter names/types and return type metadata.
+// 'set_fn_XXX' by default does not set function metadata.
+module.update_fn_metadata(hash, ["x: &mut i64", "i64"]);
 
 // Load the module into the Engine as a sub-module named 'calc'
 let mut engine = Engine::new();
diff --git a/doc/src/rust/packages/create.md b/doc/src/rust/packages/create.md
index 04911dd4..ec573804 100644
--- a/doc/src/rust/packages/create.md
+++ b/doc/src/rust/packages/create.md
@@ -50,9 +50,13 @@ def_package!(rhai:MyPackage:"My own personal super package", module, {
     BasicMapPackage::init(module);
 
     // Register additional Rust functions using the standard 'set_fn_XXX' module API.
-    module.set_fn_1("foo", |s: ImmutableString| {
+    let hash = module.set_fn_1("foo", |s: ImmutableString| {
         Ok(foo(s.into_owned()))
     });
+
+    // Remember to update the parameter names/types and return type metadata.
+    // 'set_fn_XXX' by default does not set function metadata.
+    module.update_fn_metadata(hash, ["s: ImmutableString", "i64"]);
 });
 ```
 
diff --git a/src/ast.rs b/src/ast.rs
index e89fa446..cc5a79be 100644
--- a/src/ast.rs
+++ b/src/ast.rs
@@ -89,7 +89,7 @@ impl fmt::Display for ScriptFnDef {
     fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
         write!(
             f,
-            "{}{}({})",
+            "{}{}({}) -> Dynamic",
             if self.access.is_private() {
                 "private "
             } else {
@@ -151,6 +151,7 @@ impl AST {
         &mut self.0
     }
     /// Get the internal shared [`Module`] containing all script-defined functions.
+    #[cfg(not(feature = "no_function"))]
     #[inline(always)]
     pub(crate) fn shared_lib(&self) -> Shared<Module> {
         self.1.clone()
diff --git a/src/module/mod.rs b/src/module/mod.rs
index c4d5147b..4ad40090 100644
--- a/src/module/mod.rs
+++ b/src/module/mod.rs
@@ -9,7 +9,7 @@ use crate::stdlib::{
     boxed::Box,
     collections::HashMap,
     fmt, format,
-    iter::empty,
+    iter::{empty, once},
     num::NonZeroUsize,
     ops::{Add, AddAssign, Deref, DerefMut},
     string::{String, ToString},
@@ -90,8 +90,15 @@ impl FuncInfo {
         let mut sig = format!("{}(", self.name);
 
         if let Some(ref names) = self.param_names {
-            let params: Vec<_> = names.iter().map(ImmutableString::to_string).collect();
+            let mut params: Vec<_> = names.iter().map(ImmutableString::to_string).collect();
+            let return_type = params.pop().unwrap_or_else(|| "()".to_string());
             sig.push_str(&params.join(", "));
+            if return_type != "()" {
+                sig.push_str(") -> ");
+                sig.push_str(&return_type);
+            } else {
+                sig.push_str(")");
+            }
         } else {
             for x in 0..self.params {
                 sig.push_str("_");
@@ -99,9 +106,9 @@ impl FuncInfo {
                     sig.push_str(", ");
                 }
             }
+            sig.push_str(") -> Dynamic");
         }
 
-        sig.push_str(")");
         sig
     }
 }
@@ -362,7 +369,14 @@ impl Module {
                 access: fn_def.access,
                 params: num_params,
                 param_types: None,
-                param_names: Some(fn_def.params.clone()),
+                param_names: Some(
+                    fn_def
+                        .params
+                        .iter()
+                        .cloned()
+                        .chain(once("Dynamic".into()))
+                        .collect(),
+                ),
                 func: fn_def.into(),
             },
         );
@@ -483,13 +497,22 @@ impl Module {
         }
     }
 
-    /// Update the parameter names and types in a registered function.
+    /// Update the metadata (parameter names/types and return type) of a registered function.
     ///
     /// The [`u64`] hash is calculated either by the function [`crate::calc_native_fn_hash`] or
     /// the function [`crate::calc_script_fn_hash`].
-    pub fn update_fn_param_names(&mut self, hash_fn: u64, arg_names: &[&str]) -> &mut Self {
+    ///
+    /// Each parameter name/type pair should be a single string of the format: `var_name: type`.
+    ///
+    /// The last entry in the list should be the return type of the function.
+    /// In other words, the number of entries should be one larger than the number of parameters.
+    pub fn update_fn_metadata<'a>(
+        &mut self,
+        hash_fn: u64,
+        arg_names: impl AsRef<[&'a str]>,
+    ) -> &mut Self {
         if let Some(f) = self.functions.get_mut(&hash_fn) {
-            f.param_names = Some(arg_names.iter().map(|&n| n.into()).collect());
+            f.param_names = Some(arg_names.as_ref().iter().map(|&n| n.into()).collect());
         }
         self
     }
@@ -573,6 +596,10 @@ impl Module {
     ///
     /// To access the first mutable parameter, use `args.get_mut(0).unwrap()`
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -632,6 +659,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -663,6 +694,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -696,6 +731,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -733,6 +772,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust getter function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -760,6 +803,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -799,6 +846,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -843,6 +894,10 @@ impl Module {
     ///
     /// If there is a similar existing setter Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -880,6 +935,10 @@ impl Module {
     /// Panics if the type is [`Array`] or [`Map`].
     /// Indexers for arrays, object maps and strings cannot be registered.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -918,6 +977,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -963,6 +1026,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -1018,6 +1085,10 @@ impl Module {
     /// Panics if the type is [`Array`] or [`Map`].
     /// Indexers for arrays, object maps and strings cannot be registered.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -1079,6 +1150,10 @@ impl Module {
     /// Panics if the type is [`Array`] or [`Map`].
     /// Indexers for arrays, object maps and strings cannot be registered.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -1114,6 +1189,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
@@ -1166,6 +1245,10 @@ impl Module {
     ///
     /// If there is a similar existing Rust function, it is replaced.
     ///
+    /// # Function Metadata
+    ///
+    /// No metadata for the function is registered. Use `update_fn_metadata` to add metadata.
+    ///
     /// # Example
     ///
     /// ```
diff --git a/src/packages/iter_basic.rs b/src/packages/iter_basic.rs
index 97ff0f59..4ae548e2 100644
--- a/src/packages/iter_basic.rs
+++ b/src/packages/iter_basic.rs
@@ -49,7 +49,11 @@ macro_rules! reg_range {
         $(
             $lib.set_iterator::<Range<$y>>();
             let hash = $lib.set_fn_2($x, get_range::<$y>);
-            $lib.update_fn_param_names(hash, &[concat!("from: ", stringify!($y)), concat!("to: ", stringify!($y))]);
+            $lib.update_fn_metadata(hash, [
+                    concat!("from: ", stringify!($y)),
+                    concat!("to: ", stringify!($y)),
+                    concat!("Iterator<Item=", stringify!($y), ">")
+            ]);
         )*
     )
 }
@@ -61,7 +65,11 @@ macro_rules! reg_step {
         $(
             $lib.set_iterator::<StepRange<$y>>();
             let hash = $lib.set_fn_3($x, get_step_range::<$y>);
-            $lib.update_fn_param_names(hash, &[concat!("from: ", stringify!($y)), concat!("to: ", stringify!($y)), concat!("step: ", stringify!($y))]);
+            $lib.update_fn_metadata(hash, [
+                    concat!("from: ", stringify!($y)),
+                    concat!("to: ", stringify!($y)),
+                    concat!("step: ", stringify!($y)), concat!("Iterator<Item=", stringify!($y), ">")
+            ]);
         )*
     )
 }
@@ -69,7 +77,7 @@ macro_rules! reg_step {
 def_package!(crate:BasicIteratorPackage:"Basic range iterators.", lib, {
     lib.set_iterator::<Range<INT>>();
     let hash = lib.set_fn_2("range", get_range::<INT>);
-    lib.update_fn_param_names(hash, &["from: INT", "to: INT"]);
+    lib.update_fn_metadata(hash, ["from: INT", "to: INT", "Iterator<Item=INT>"]);
 
     #[cfg(not(feature = "only_i32"))]
     #[cfg(not(feature = "only_i64"))]
@@ -83,7 +91,7 @@ def_package!(crate:BasicIteratorPackage:"Basic range iterators.", lib, {
 
     lib.set_iterator::<StepRange<INT>>();
     let hash = lib.set_fn_3("range", get_step_range::<INT>);
-    lib.update_fn_param_names(hash, &["from: INT", "to: INT", "step: INT"]);
+    lib.update_fn_metadata(hash, ["from: INT", "to: INT", "step: INT", "Iterator<Item=INT>"]);
 
     #[cfg(not(feature = "only_i32"))]
     #[cfg(not(feature = "only_i64"))]
diff --git a/src/plugin.rs b/src/plugin.rs
index 91385628..d07cc188 100644
--- a/src/plugin.rs
+++ b/src/plugin.rs
@@ -38,4 +38,7 @@ pub trait PluginFunction {
 
     /// Return a boxed slice of type ID's of the function's parameters.
     fn input_types(&self) -> Box<[TypeId]>;
+
+    /// Return a string slice of the function's return type.
+    fn return_type(&self) -> &'static str;
 }