Add calling metamethods

src/vm/mod.rs

@@ -182,6 +182,14 @@ impl Debug for Instruction {
 pub enum RuntimeError {
     #[error("Unable to perform {0:?} operator between {1:?} and {2:?}")]
     InvalidOperands(BinaryOperator, Value, Value),
+    #[error("Unable to call metamethod {0} for values {1:?} and {2:?}")]
+    InvalidOperation(String, Value, Value),
+    #[error("Metatable is not a table: {0:?}")]
+    MetatableNotTable(Value),
+    #[error("Metafunction not found: {0}")]
+    MetafunctionNotFound(String),
+    #[error("Metafunction is not callable: {0:?}")]
+    MetafunctionNotCallable(Value),
     #[error("Unable to perform {0:?} operator to {1:?}")]
     InvalidOperand(UnaryOperator, Value),
     #[error("Tried calling a non-function: {0:?}")]
@@ -751,7 +759,15 @@ impl ClosureRunner {
 
                 Instruction::Add(res, lhs, rhs) => {
                     let (lhs, rhs) = self.lhs_and_rhs(lhs, rhs);
-                    self.set_stack(*res, StackValue::Value(lhs.add(&rhs)?));
+                    self.set_stack(
+                        *res,
+                        StackValue::Value(self.result_or_metamethod(
+                            lhs.add(&rhs),
+                            "__add",
+                            lhs,
+                            rhs,
+                        )?),
+                    );
                 }
                 Instruction::Mult(res, lhs, rhs) => {
                     let (lhs, rhs) = self.lhs_and_rhs(lhs, rhs);
@@ -909,6 +925,68 @@ impl ClosureRunner {
         }
     }
 
+    fn result_or_metamethod(
+        &self,
+        value: Result<Value, RuntimeError>,
+        metamethod: &str,
+        lhs: Value,
+        rhs: Value,
+    ) -> Result<Value, RuntimeError> {
+        match value {
+            Ok(value) => Ok(value),
+            Err(_) => match (&lhs, &rhs) {
+                (Value::Table { metatable, .. }, _) => {
+                    self.call_metamethod(*metatable.clone(), metamethod, vec![lhs, rhs])
+                }
+                (_, Value::Table { metatable, .. }) => {
+                    self.call_metamethod(*metatable.clone(), metamethod, vec![rhs, lhs])
+                }
+                _ => Err(RuntimeError::InvalidOperation(
+                    metamethod.to_owned(),
+                    lhs,
+                    rhs,
+                )),
+            },
+        }
+    }
+
+    fn call_metamethod(
+        &self,
+        metatable: Value,
+        metamethod: &str,
+        params: Vec<Value>,
+    ) -> Result<Value, RuntimeError> {
+        match metatable {
+            Value::Table { contents, .. } => {
+                if let Some(value) = contents
+                    .borrow()
+                    .get(&IndexableValue::String(metamethod.to_owned()))
+                {
+                    match value {
+                        Value::RustFunction(function) => {
+                            let result = function.borrow_mut().execute(params)?;
+                            Ok(result.into_iter().next().unwrap())
+                        }
+                        Value::Function(closure) => {
+                            let mut runnable = closure.run(params);
+                            #[allow(unused_assignments)]
+                            let mut return_value = None;
+                            while {
+                                return_value = runnable.next()?;
+                                return_value.is_none()
+                            } {}
+                            Ok(return_value.unwrap().into_iter().next().unwrap())
+                        }
+                        _ => Err(RuntimeError::MetafunctionNotCallable(value.clone())),
+                    }
+                } else {
+                    Err(RuntimeError::MetafunctionNotFound(metamethod.to_owned()))
+                }
+            }
+            _ => Err(RuntimeError::MetatableNotTable(metatable)),
+        }
+    }
+
     fn lhs_and_rhs(&self, lhs: &u16, rhs: &u16) -> (Value, Value) {
         (
             self.stack