Add test; Make garbage collection work

src/abstract_tree/assignment.rs

@@ -63,8 +63,6 @@ impl AbstractTree for Assignment {
             context.set_type(self.identifier.clone(), r#type)?;
         }
 
-        self.identifier.validate(source, context)?;
-
         if let Some(type_specification) = &self.type_specification {
             match self.operator {
                 AssignmentOperator::Equal => {
@@ -135,13 +133,9 @@ impl AbstractTree for Assignment {
 
         let new_value = match self.operator {
             AssignmentOperator::PlusEqual => {
-                if let Some(left) = context.get_value(&self.identifier)? {
-                    left.add(right, self.syntax_position)?
-                } else {
-                    return Err(RuntimeError::ValidationFailure(
-                        ValidationError::VariableIdentifierNotFound(self.identifier.clone()),
-                    ));
-                }
+                let left = self.identifier.run(source, context)?;
+
+                left.add(right, self.syntax_position)?
             }
             AssignmentOperator::MinusEqual => {
                 if let Some(left) = context.get_value(&self.identifier)? {

src/context/mod.rs

@@ -180,6 +180,8 @@ impl Context {
     /// representing whether or not the variable was found.
     pub fn add_allowance(&self, identifier: &Identifier) -> Result<bool, RwLockError> {
         if let Some((_value_data, counter)) = self.inner.read()?.get(identifier) {
+            log::debug!("Adding allowance for {identifier}.");
+
             counter.add_allowance()?;
 
             Ok(true)
@@ -207,7 +209,13 @@ impl Context {
                 return Ok(None);
             };
 
-        if counter.allowances() == counter.runtime_uses() {
+        counter.add_runtime_use()?;
+
+        log::debug!("Adding runtime use for {identifier}.");
+
+        let (allowances, runtime_uses) = counter.get_counts()?;
+
+        if allowances == runtime_uses {
             self.unset(identifier)?;
         }
 
@@ -371,3 +379,26 @@ impl Display for Context {
         writeln!(f, "}}")
     }
 }
+
+#[cfg(test)]
+mod tests {
+    use crate::*;
+
+    #[test]
+    fn drops_variables() {
+        let context = Context::new();
+
+        interpret_with_context(
+            "
+                x = 1
+                y = 2
+
+                z = x + y
+            ",
+            context.clone(),
+        )
+        .unwrap();
+
+        assert_eq!(context.inner.read().unwrap().len(), 1);
+    }
+}

src/context/usage_counter.rs

@@ -16,12 +16,9 @@ impl UsageCounter {
         })))
     }
 
-    pub fn allowances(&self) -> Result<usize, RwLockError> {
-        Ok(self.0.read()?.allowances)
-    }
-
-    pub fn runtime_uses(&self) -> Result<usize, RwLockError> {
-        Ok(self.0.read()?.runtime_uses)
+    pub fn get_counts(&self) -> Result<(usize, usize), RwLockError> {
+        let inner = self.0.read()?;
+        Ok((inner.allowances, inner.runtime_uses))
     }
 
     pub fn add_allowance(&self) -> Result<(), RwLockError> {