The Value matches existed only to keep conversion inside the frame
where caller_position could prefix the config line; deferring that for
simpler signatures, with mlua bad-argument errors surfacing the call
site in the traceback meanwhile.

Assisted-by: GLM-5.3 via pi

diff --git a/src/parallax.rs b/src/parallax.rs
index b71b355..63c2c52 100644
--- a/src/parallax.rs
+++ b/src/parallax.rs
@@ -29,10 +29,7 @@ struct Registrations {
 }
 
 impl Registrations {
-    fn setup(&mut self, lua: &Lua, table: Value) -> Result<(), mlua::Error> {
-        let Value::Table(table) = table else {
-            return Err(error_at(lua, "setup takes a table"));
-        };
+    fn setup(&mut self, lua: &Lua, table: Table) -> Result<(), mlua::Error> {
         if self.setup.is_some() {
             return Err(error_at(lua, "setup must be called exactly once"));
         }
@@ -46,10 +43,7 @@ impl Registrations {
         Ok(())
     }
 
-    fn server(&mut self, lua: &Lua, call: Value) -> Result<(), mlua::Error> {
-        let Value::Function(call) = call else {
-            return Err(error_at(lua, "server takes a function"));
-        };
+    fn server(&mut self, lua: &Lua, call: Function) -> Result<(), mlua::Error> {
         if self.server.is_some() {
             return Err(error_at(lua, "server must be called exactly once"));
         }
@@ -57,10 +51,7 @@ impl Registrations {
         Ok(())
     }
 
-    fn flow(&mut self, lua: &Lua, call: Value) -> Result<(), mlua::Error> {
-        let Value::Function(call) = call else {
-            return Err(error_at(lua, "flow takes a function"));
-        };
+    fn flow(&mut self, lua: &Lua, call: Function) -> Result<(), mlua::Error> {
         if self.flow.is_some() {
             return Err(error_at(lua, "flow must be called exactly once"));
         }
@@ -165,19 +156,19 @@ fn install_module(lua: &Lua) -> Result<AnyUserData, mlua::Error> {
 
     let setup = {
         let module = module.clone();
-        lua.create_function(move |lua, table: Value| {
+        lua.create_function(move |lua, table: Table| {
             module.borrow_mut::<Registrations>()?.setup(lua, table)
         })?
     };
     let server = {
         let module = module.clone();
-        lua.create_function(move |lua, call: Value| {
+        lua.create_function(move |lua, call: Function| {
             module.borrow_mut::<Registrations>()?.server(lua, call)
         })?
     };
     let flow = {
         let module = module.clone();
-        lua.create_function(move |lua, call: Value| {
+        lua.create_function(move |lua, call: Function| {
             module.borrow_mut::<Registrations>()?.flow(lua, call)
         })?
     };
diff --git a/tests/cli.rs b/tests/cli.rs
index ade03eb..38ab3b9 100644
--- a/tests/cli.rs
+++ b/tests/cli.rs
@@ -181,9 +181,7 @@ fn duplicate_flow_registration_fails() {
         .arg(&path)
         .assert()
         .failure()
-        .stderr(
-            predicate::str::contains("config.fnl:5:").and(predicate::str::contains("exactly")),
-        );
+        .stderr(predicate::str::contains("config.fnl:5:").and(predicate::str::contains("exactly")));
 }
 
 #[test]
@@ -201,7 +199,8 @@ fn malformed_flow_registration_fails() {
         .assert()
         .failure()
         .stderr(
-            predicate::str::contains("config.fnl:4:").and(predicate::str::contains("flow takes")),
+            predicate::str::contains("bad argument #1")
+                .and(predicate::str::contains("config.fnl:4:")),
         );
 }