diff --git a/dust-lang/src/abstract_tree/assignment.rs b/dust-lang/src/abstract_tree/assignment.rs
index 423f4b1..d0da851 100644
--- a/dust-lang/src/abstract_tree/assignment.rs
+++ b/dust-lang/src/abstract_tree/assignment.rs
@@ -39,11 +39,11 @@ impl Assignment {
 }
 
 impl AbstractNode for Assignment {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
 
-    fn validate(&self, context: &Context, manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, context: &mut Context, manage_memory: bool) -> Result<(), ValidationError> {
         let statement_type = self.statement.expected_type(context)?;
 
         if let Some(WithPosition {
diff --git a/dust-lang/src/abstract_tree/async_block.rs b/dust-lang/src/abstract_tree/async_block.rs
index cc92d80..fdc0b32 100644
--- a/dust-lang/src/abstract_tree/async_block.rs
+++ b/dust-lang/src/abstract_tree/async_block.rs
@@ -21,11 +21,11 @@ impl AsyncBlock {
 }
 
 impl AbstractNode for AsyncBlock {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         self.statements.last().unwrap().expected_type(_context)
     }
 
-    fn validate(&self, _context: &Context, manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, _context: &mut Context, manage_memory: bool) -> Result<(), ValidationError> {
         for statement in &self.statements {
             statement.validate(_context, manage_memory)?;
         }
@@ -33,7 +33,7 @@ impl AbstractNode for AsyncBlock {
         Ok(())
     }
 
-    fn run(self, _context: &mut Context, manage_memory: bool) -> Result<Action, RuntimeError> {
+    fn run(self, _context: &mut Context, _manage_memory: bool) -> Result<Action, RuntimeError> {
         let statement_count = self.statements.len();
         let final_result = RwLock::new(Ok(Action::None));
 
@@ -41,7 +41,7 @@ impl AbstractNode for AsyncBlock {
             .into_par_iter()
             .enumerate()
             .find_map_first(|(index, statement)| {
-                let result = statement.run(&mut _context.clone(), manage_memory);
+                let result = statement.run(&mut _context.clone(), false);
 
                 if index == statement_count - 1 {
                     let get_write_lock = final_result.write();
diff --git a/dust-lang/src/abstract_tree/block.rs b/dust-lang/src/abstract_tree/block.rs
index e43b560..5597a7c 100644
--- a/dust-lang/src/abstract_tree/block.rs
+++ b/dust-lang/src/abstract_tree/block.rs
@@ -21,7 +21,7 @@ impl Block {
 }
 
 impl AbstractNode for Block {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         if let Some(statement) = self.statements.last() {
             statement.expected_type(_context)
         } else {
@@ -29,7 +29,11 @@ impl AbstractNode for Block {
         }
     }
 
-    fn validate(&self, _context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(
+        &self,
+        _context: &mut Context,
+        _manage_memory: bool,
+    ) -> Result<(), ValidationError> {
         for statement in &self.statements {
             statement.validate(_context, _manage_memory)?;
         }
@@ -88,6 +92,6 @@ mod tests {
             )),
         ]);
 
-        assert_eq!(block.expected_type(&Context::new()), Ok(Type::Integer))
+        assert_eq!(block.expected_type(&mut Context::new()), Ok(Type::Integer))
     }
 }
diff --git a/dust-lang/src/abstract_tree/built_in_function_call.rs b/dust-lang/src/abstract_tree/built_in_function_call.rs
index 8190580..e710d52 100644
--- a/dust-lang/src/abstract_tree/built_in_function_call.rs
+++ b/dust-lang/src/abstract_tree/built_in_function_call.rs
@@ -18,7 +18,7 @@ pub enum BuiltInFunctionCall {
 }
 
 impl AbstractNode for BuiltInFunctionCall {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         match self {
             BuiltInFunctionCall::ReadLine => Ok(Type::String),
             BuiltInFunctionCall::Sleep(_) => Ok(Type::None),
@@ -26,7 +26,11 @@ impl AbstractNode for BuiltInFunctionCall {
         }
     }
 
-    fn validate(&self, _context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(
+        &self,
+        _context: &mut Context,
+        _manage_memory: bool,
+    ) -> Result<(), ValidationError> {
         match self {
             BuiltInFunctionCall::ReadLine => Ok(()),
             BuiltInFunctionCall::Sleep(expression) => expression.validate(_context, _manage_memory),
diff --git a/dust-lang/src/abstract_tree/expression.rs b/dust-lang/src/abstract_tree/expression.rs
index 40933e1..9b58498 100644
--- a/dust-lang/src/abstract_tree/expression.rs
+++ b/dust-lang/src/abstract_tree/expression.rs
@@ -37,7 +37,7 @@ impl Expression {
 }
 
 impl AbstractNode for Expression {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         match self {
             Expression::FunctionCall(function_call) => function_call.item.expected_type(_context),
             Expression::Identifier(identifier) => {
@@ -61,7 +61,7 @@ impl AbstractNode for Expression {
         }
     }
 
-    fn validate(&self, context: &Context, manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, context: &mut Context, manage_memory: bool) -> Result<(), ValidationError> {
         match self {
             Expression::FunctionCall(function_call) => {
                 function_call.item.validate(context, manage_memory)
diff --git a/dust-lang/src/abstract_tree/function_call.rs b/dust-lang/src/abstract_tree/function_call.rs
index dac1e8f..5562e9c 100644
--- a/dust-lang/src/abstract_tree/function_call.rs
+++ b/dust-lang/src/abstract_tree/function_call.rs
@@ -28,7 +28,7 @@ impl FunctionCall {
 }
 
 impl AbstractNode for FunctionCall {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         let function_node_type = self.function.expected_type(_context)?;
 
         if let Type::Function { return_type, .. } = function_node_type {
@@ -41,7 +41,7 @@ impl AbstractNode for FunctionCall {
         }
     }
 
-    fn validate(&self, context: &Context, manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, context: &mut Context, manage_memory: bool) -> Result<(), ValidationError> {
         self.function.validate(context, manage_memory)?;
 
         for expression in &self.arguments {
diff --git a/dust-lang/src/abstract_tree/if_else.rs b/dust-lang/src/abstract_tree/if_else.rs
index 3ae0e7c..bae77b2 100644
--- a/dust-lang/src/abstract_tree/if_else.rs
+++ b/dust-lang/src/abstract_tree/if_else.rs
@@ -31,11 +31,11 @@ impl IfElse {
 }
 
 impl AbstractNode for IfElse {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         self.if_block.item.expected_type(_context)
     }
 
-    fn validate(&self, context: &Context, manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, context: &mut Context, manage_memory: bool) -> Result<(), ValidationError> {
         self.if_expression.validate(context, manage_memory)?;
         self.if_block.item.validate(context, manage_memory)?;
 
diff --git a/dust-lang/src/abstract_tree/list_index.rs b/dust-lang/src/abstract_tree/list_index.rs
index ec27318..e104299 100644
--- a/dust-lang/src/abstract_tree/list_index.rs
+++ b/dust-lang/src/abstract_tree/list_index.rs
@@ -18,7 +18,7 @@ impl ListIndex {
 }
 
 impl AbstractNode for ListIndex {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         let left_type = self.left.expected_type(_context)?;
 
         if let (
@@ -47,7 +47,7 @@ impl AbstractNode for ListIndex {
         }
     }
 
-    fn validate(&self, context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, context: &mut Context, _manage_memory: bool) -> Result<(), ValidationError> {
         self.left.validate(context, _manage_memory)?;
         self.right.validate(context, _manage_memory)?;
 
diff --git a/dust-lang/src/abstract_tree/logic.rs b/dust-lang/src/abstract_tree/logic.rs
index e2aa975..502ec96 100644
--- a/dust-lang/src/abstract_tree/logic.rs
+++ b/dust-lang/src/abstract_tree/logic.rs
@@ -21,11 +21,11 @@ pub enum Logic {
 }
 
 impl AbstractNode for Logic {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         Ok(Type::Boolean)
     }
 
-    fn validate(&self, context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, context: &mut Context, _manage_memory: bool) -> Result<(), ValidationError> {
         match self {
             Logic::Equal(left, right)
             | Logic::NotEqual(left, right)
diff --git a/dust-lang/src/abstract_tree/loop.rs b/dust-lang/src/abstract_tree/loop.rs
index a2cdd78..506fa44 100644
--- a/dust-lang/src/abstract_tree/loop.rs
+++ b/dust-lang/src/abstract_tree/loop.rs
@@ -17,11 +17,15 @@ impl Loop {
 }
 
 impl AbstractNode for Loop {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
 
-    fn validate(&self, _context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(
+        &self,
+        _context: &mut Context,
+        _manage_memory: bool,
+    ) -> Result<(), ValidationError> {
         for statement in &self.statements {
             statement.validate(_context, false)?;
         }
diff --git a/dust-lang/src/abstract_tree/map_index.rs b/dust-lang/src/abstract_tree/map_index.rs
index 9452d78..79c7dfe 100644
--- a/dust-lang/src/abstract_tree/map_index.rs
+++ b/dust-lang/src/abstract_tree/map_index.rs
@@ -23,7 +23,7 @@ impl MapIndex {
 }
 
 impl AbstractNode for MapIndex {
-    fn expected_type(&self, context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, context: &mut Context) -> Result<Type, ValidationError> {
         if let (Expression::Identifier(collection_identifier), index) =
             (&self.collection, &self.index)
         {
@@ -105,7 +105,11 @@ impl AbstractNode for MapIndex {
         })
     }
 
-    fn validate(&self, _context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(
+        &self,
+        _context: &mut Context,
+        _manage_memory: bool,
+    ) -> Result<(), ValidationError> {
         self.collection.validate(_context, _manage_memory)
     }
 
diff --git a/dust-lang/src/abstract_tree/math.rs b/dust-lang/src/abstract_tree/math.rs
index 293bf13..dde5079 100644
--- a/dust-lang/src/abstract_tree/math.rs
+++ b/dust-lang/src/abstract_tree/math.rs
@@ -17,7 +17,7 @@ pub enum Math {
 }
 
 impl AbstractNode for Math {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         match self {
             Math::Add(left, right)
             | Math::Subtract(left, right)
@@ -40,7 +40,7 @@ impl AbstractNode for Math {
         }
     }
 
-    fn validate(&self, context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, context: &mut Context, _manage_memory: bool) -> Result<(), ValidationError> {
         match self {
             Math::Add(left, right) => {
                 let left_position = left.position();
diff --git a/dust-lang/src/abstract_tree/mod.rs b/dust-lang/src/abstract_tree/mod.rs
index a1191e7..12c7102 100644
--- a/dust-lang/src/abstract_tree/mod.rs
+++ b/dust-lang/src/abstract_tree/mod.rs
@@ -182,7 +182,7 @@ impl Index<usize> for AbstractTree {
 }
 
 pub trait AbstractNode: Sized {
-    fn expected_type(&self, context: &Context) -> Result<Type, ValidationError>;
-    fn validate(&self, context: &Context, manage_memory: bool) -> Result<(), ValidationError>;
+    fn expected_type(&self, context: &mut Context) -> Result<Type, ValidationError>;
+    fn validate(&self, context: &mut Context, manage_memory: bool) -> Result<(), ValidationError>;
     fn run(self, context: &mut Context, manage_memory: bool) -> Result<Action, RuntimeError>;
 }
diff --git a/dust-lang/src/abstract_tree/statement.rs b/dust-lang/src/abstract_tree/statement.rs
index bed7991..cd23513 100644
--- a/dust-lang/src/abstract_tree/statement.rs
+++ b/dust-lang/src/abstract_tree/statement.rs
@@ -38,7 +38,7 @@ impl Statement {
 }
 
 impl AbstractNode for Statement {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         match self {
             Statement::Assignment(assignment) => assignment.item.expected_type(_context),
             Statement::AsyncBlock(async_block) => async_block.item.expected_type(_context),
@@ -54,7 +54,11 @@ impl AbstractNode for Statement {
         }
     }
 
-    fn validate(&self, _context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(
+        &self,
+        _context: &mut Context,
+        _manage_memory: bool,
+    ) -> Result<(), ValidationError> {
         match self {
             Statement::Assignment(assignment) => assignment.item.validate(_context, _manage_memory),
             Statement::AsyncBlock(async_block) => {
diff --git a/dust-lang/src/abstract_tree/structure_definition.rs b/dust-lang/src/abstract_tree/structure_definition.rs
index abee81f..366a454 100644
--- a/dust-lang/src/abstract_tree/structure_definition.rs
+++ b/dust-lang/src/abstract_tree/structure_definition.rs
@@ -19,11 +19,15 @@ impl StructureDefinition {
 }
 
 impl AbstractNode for StructureDefinition {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
 
-    fn validate(&self, _context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(
+        &self,
+        _context: &mut Context,
+        _manage_memory: bool,
+    ) -> Result<(), ValidationError> {
         Ok(())
     }
 
diff --git a/dust-lang/src/abstract_tree/type.rs b/dust-lang/src/abstract_tree/type.rs
index fdec583..a13c342 100644
--- a/dust-lang/src/abstract_tree/type.rs
+++ b/dust-lang/src/abstract_tree/type.rs
@@ -144,11 +144,15 @@ impl Type {
 }
 
 impl AbstractNode for Type {
-    fn expected_type(&self, _: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _: &mut Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
 
-    fn validate(&self, _context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(
+        &self,
+        _context: &mut Context,
+        _manage_memory: bool,
+    ) -> Result<(), ValidationError> {
         Ok(())
     }
 
diff --git a/dust-lang/src/abstract_tree/value_node.rs b/dust-lang/src/abstract_tree/value_node.rs
index 27280c9..2202434 100644
--- a/dust-lang/src/abstract_tree/value_node.rs
+++ b/dust-lang/src/abstract_tree/value_node.rs
@@ -31,7 +31,7 @@ pub enum ValueNode {
 }
 
 impl AbstractNode for ValueNode {
-    fn expected_type(&self, context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, context: &mut Context) -> Result<Type, ValidationError> {
         let r#type = match self {
             ValueNode::Boolean(_) => Type::Boolean,
             ValueNode::Float(_) => Type::Float,
@@ -91,7 +91,7 @@ impl AbstractNode for ValueNode {
         Ok(r#type)
     }
 
-    fn validate(&self, context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(&self, context: &mut Context, _manage_memory: bool) -> Result<(), ValidationError> {
         if let ValueNode::Map(map_assignments) = self {
             for (_identifier, r#type, expression) in map_assignments {
                 if let Some(expected_type) = r#type {
@@ -117,7 +117,7 @@ impl AbstractNode for ValueNode {
             body,
         } = self
         {
-            let function_context = Context::new();
+            let mut function_context = Context::new();
 
             function_context.inherit_types_from(context)?;
 
@@ -131,9 +131,9 @@ impl AbstractNode for ValueNode {
                 function_context.set_type(identifier.clone(), r#type.item.clone())?;
             }
 
-            body.item.validate(&function_context, _manage_memory)?;
+            body.item.validate(&mut function_context, _manage_memory)?;
 
-            let actual_return_type = body.item.expected_type(&function_context)?;
+            let actual_return_type = body.item.expected_type(&mut function_context)?;
 
             return_type
                 .item
diff --git a/dust-lang/src/abstract_tree/while.rs b/dust-lang/src/abstract_tree/while.rs
index ddc92fa..7a42c31 100644
--- a/dust-lang/src/abstract_tree/while.rs
+++ b/dust-lang/src/abstract_tree/while.rs
@@ -23,11 +23,15 @@ impl While {
 }
 
 impl AbstractNode for While {
-    fn expected_type(&self, _context: &Context) -> Result<Type, ValidationError> {
+    fn expected_type(&self, _context: &mut Context) -> Result<Type, ValidationError> {
         Ok(Type::None)
     }
 
-    fn validate(&self, _context: &Context, _manage_memory: bool) -> Result<(), ValidationError> {
+    fn validate(
+        &self,
+        _context: &mut Context,
+        _manage_memory: bool,
+    ) -> Result<(), ValidationError> {
         self.expression.validate(_context, _manage_memory)?;
 
         for statement in &self.statements {
diff --git a/dust-lang/src/context.rs b/dust-lang/src/context.rs
index 6d1aef2..256d070 100644
--- a/dust-lang/src/context.rs
+++ b/dust-lang/src/context.rs
@@ -78,12 +78,16 @@ impl Context {
         }
     }
 
-    pub fn use_value(&self, identifier: &Identifier) -> Result<Option<Value>, RwLockPoisonError> {
+    pub fn use_value(
+        &mut self,
+        identifier: &Identifier,
+    ) -> Result<Option<Value>, RwLockPoisonError> {
         if let Some((ValueData::Value(value), usage_data)) = self.variables.read()?.get(identifier)
         {
             log::trace!("Using {identifier}'s value.");
 
             usage_data.inner().write()?.actual += 1;
+            self.is_clean = false;
 
             Ok(Some(value.clone()))
         } else {
@@ -111,7 +115,11 @@ impl Context {
         Ok(())
     }
 
-    pub fn set_value(&self, identifier: Identifier, value: Value) -> Result<(), RwLockPoisonError> {
+    pub fn set_value(
+        &mut self,
+        identifier: Identifier,
+        value: Value,
+    ) -> Result<(), RwLockPoisonError> {
         log::debug!("Setting {identifier} to value {value}.");
 
         let mut variables = self.variables.write()?;
@@ -156,6 +164,22 @@ impl Context {
         Ok(())
     }
 
+    pub fn is_clean(&mut self) -> Result<bool, RwLockPoisonError> {
+        if self.is_clean {
+            Ok(true)
+        } else {
+            for (_, (_, usage_data)) in self.variables.read()?.iter() {
+                let usage_data = usage_data.inner().read().unwrap();
+
+                if usage_data.actual > usage_data.expected {
+                    return Ok(false);
+                }
+            }
+
+            Ok(true)
+        }
+    }
+
     pub fn add_expected_use(&self, identifier: &Identifier) -> Result<bool, RwLockPoisonError> {
         if let Some((_, usage_data)) = self.variables.read()?.get(identifier) {
             log::trace!("Adding expected use for variable {identifier}.");