Reimplemented Melo

- Variable made into enum of `ValueRef or Melo`
- Melo-ing variable causes dropping of the Rc, decreasing reference count

ablescript/src/interpret.rs

@@ -198,7 +198,9 @@ impl ExecEnv {
 
             // TODO: not too happy with constructing an artificial
             // Ident here.
-            Variable(name) => self.get_var(&Spanned::new(name.to_owned(), expr.span.clone()))?,
+            Variable(name) => {
+                self.get_var_value(&Spanned::new(name.to_owned(), expr.span.clone()))?
+            }
         })
     }
 
@@ -275,7 +277,7 @@ impl ExecEnv {
                 return Ok(HaltStatus::Hopback(stmt.span.clone()));
             }
             Stmt::Melo(ident) => {
-                self.get_var_mut(ident)?.melo = true;
+                *self.get_var_mut(ident)? = Variable::Melo;
             }
             Stmt::Rlyeh => {
                 // Maybe print a creepy error message or something
@@ -305,7 +307,7 @@ impl ExecEnv {
     fn assign(&mut self, dest: &Assignable, value: Value) -> Result<(), Error> {
         match dest.kind {
             AssignableKind::Variable => {
-                self.get_var_mut(&dest.ident)?.value.replace(value);
+                self.get_var_rc(&dest.ident)?.replace(value);
             }
             AssignableKind::Index { ref indices } => {
                 let mut cell = self.get_var_rc(&dest.ident)?;
@@ -514,7 +516,7 @@ impl ExecEnv {
 
     /// Get the value of a variable. Throw an error if the variable is
     /// inaccessible or banned.
-    fn get_var(&self, name: &Spanned<String>) -> Result<Value, Error> {
+    fn get_var_value(&self, name: &Spanned<String>) -> Result<Value, Error> {
         // Search for the name in the stack from top to bottom.
         match self
             .stack
@@ -522,16 +524,11 @@ impl ExecEnv {
             .rev()
             .find_map(|scope| scope.variables.get(&name.item))
         {
-            Some(var) => {
-                if !var.melo {
-                    Ok(var.value.borrow().clone())
-                } else {
-                    Err(Error {
+            Some(Variable::Ref(r)) => Ok(r.borrow().clone()),
+            Some(Variable::Melo) => Err(Error {
                 kind: ErrorKind::MeloVariable(name.item.to_owned()),
                 span: name.span.clone(),
-                    })
-                }
-            }
+            }),
             None => Err(Error {
                 kind: ErrorKind::UnknownVariable(name.item.to_owned()),
                 span: name.span.clone(),
@@ -550,16 +547,7 @@ impl ExecEnv {
             .rev()
             .find_map(|scope| scope.variables.get_mut(&name.item))
         {
-            Some(var) => {
-                if !var.melo {
-                    Ok(var)
-                } else {
-                    Err(Error {
-                        kind: ErrorKind::MeloVariable(name.item.to_owned()),
-                        span: name.span.clone(),
-                    })
-                }
-            }
+            Some(var) => Ok(var),
             None => Err(Error {
                 kind: ErrorKind::UnknownVariable(name.item.to_owned()),
                 span: name.span.clone(),
@@ -570,7 +558,13 @@ impl ExecEnv {
     /// Get an Rc'd pointer to the value of a variable. Throw an error
     /// if the variable is inaccessible or banned.
     fn get_var_rc(&mut self, name: &Spanned<String>) -> Result<ValueRef, Error> {
-        Ok(self.get_var_mut(name)?.value.clone())
+        match self.get_var_mut(name)? {
+            Variable::Ref(r) => Ok(r.clone()),
+            Variable::Melo => Err(Error {
+                kind: ErrorKind::MeloVariable(name.item.to_owned()),
+                span: name.span.clone(),
+            }),
+        }
     }
 
     /// Declare a new variable, with the given initial value.
@@ -585,7 +579,7 @@ impl ExecEnv {
             .last()
             .expect("Declaring variable on empty stack")
             .variables
-            .insert(name.to_owned(), Variable { melo: false, value });
+            .insert(name.to_owned(), Variable::Ref(value));
     }
 }
 
@@ -709,7 +703,7 @@ mod tests {
         // Declaring and reading from a variable.
         eval(&mut env, "dim foo 32; dim bar foo + 1;").unwrap();
         assert_eq!(
-            env.get_var(&Spanned {
+            env.get_var_value(&Spanned {
                 item: "bar".to_owned(),
                 span: 1..1,
             })
@@ -720,7 +714,7 @@ mod tests {
         // Assigning an existing variable.
         eval(&mut env, "/*hi*/ =: foo;").unwrap();
         assert_eq!(
-            env.get_var(&Spanned {
+            env.get_var_value(&Spanned {
                 item: "foo".to_owned(),
                 span: 1..1,
             })
@@ -746,7 +740,7 @@ mod tests {
         .unwrap();
 
         assert_eq!(
-            env.get_var(&Spanned {
+            env.get_var_value(&Spanned {
                 item: "foo".to_owned(),
                 span: 1..1,
             })

ablescript/src/variables.rs

@@ -971,19 +971,13 @@ impl ValueRef {
 }
 
 #[derive(Debug)]
-pub struct Variable {
-    pub melo: bool,
-
-    // Multiple Variables can reference the same underlying Value when
-    // pass-by-reference is used, therefore we use Rc here.
-    pub value: ValueRef,
+pub enum Variable {
+    Ref(ValueRef),
+    Melo,
 }
 
 impl Variable {
     pub fn from_value(value: Value) -> Self {
-        Self {
-            melo: false,
-            value: ValueRef::new(value),
-        }
+        Self::Ref(ValueRef::new(value))
     }
 }