diff --git a/src/abstract_tree/function_call.rs b/src/abstract_tree/function_call.rs
index 202d816..e3316dd 100644
--- a/src/abstract_tree/function_call.rs
+++ b/src/abstract_tree/function_call.rs
@@ -120,14 +120,7 @@ impl AbstractTree for FunctionCall {
             context.set(name.to_string(), value.clone(), None)?;
         }
 
-        value
-            .as_function()
-            .map_err(|error| {
-                println!("{name:?}");
-
-                error
-            })?
-            .call(name, &arguments, source, context)
+        value.as_function()?.call(name, &arguments, source, context)
     }
 
     fn expected_type(&self, context: &Map) -> Result<Type> {
diff --git a/src/abstract_tree/function_node.rs b/src/abstract_tree/function_node.rs
index 57bb654..ef1e58f 100644
--- a/src/abstract_tree/function_node.rs
+++ b/src/abstract_tree/function_node.rs
@@ -14,6 +14,7 @@ pub struct FunctionNode {
     body: Block,
     r#type: Type,
     syntax_position: SyntaxPosition,
+    context: Map,
 }
 
 impl FunctionNode {
@@ -22,12 +23,14 @@ impl FunctionNode {
         body: Block,
         r#type: Type,
         syntax_position: SyntaxPosition,
+        context: Map,
     ) -> Self {
         Self {
             parameters,
             body,
             r#type,
             syntax_position,
+            context,
         }
     }
 
@@ -61,23 +64,24 @@ impl FunctionNode {
         outer_context: &Map,
     ) -> Result<Value> {
         let parameter_argument_pairs = self.parameters.iter().zip(arguments.iter());
-        let function_context = Map::clone_from(outer_context)?;
+
+        self.context.clone_complex_values_from(outer_context)?;
 
         for (identifier, value) in parameter_argument_pairs {
             let key = identifier.inner().clone();
 
-            function_context.set(key, value.clone(), None)?;
+            self.context.set(key, value.clone(), None)?;
         }
 
         if let Some(name) = name {
-            function_context.set(
+            self.context.set(
                 name,
                 Value::Function(Function::ContextDefined(self.clone())),
                 None,
             )?;
         }
 
-        let return_value = self.body.run(source, &function_context)?;
+        let return_value = self.body.run(source, &self.context)?;
 
         Ok(return_value)
     }
@@ -107,7 +111,9 @@ impl AbstractTree for FunctionNode {
             }
         }
 
-        let function_context = Map::clone_from(context)?;
+        let function_context = Map::new();
+
+        function_context.clone_complex_values_from(context)?;
 
         for (parameter_name, parameter_type) in parameters.iter().zip(parameter_types.iter()) {
             function_context.set(
@@ -126,14 +132,22 @@ impl AbstractTree for FunctionNode {
         let r#type = Type::function(parameter_types, return_type.take_inner());
         let syntax_position = node.range().into();
 
-        Ok(FunctionNode::new(parameters, body, r#type, syntax_position))
+        Ok(FunctionNode::new(
+            parameters,
+            body,
+            r#type,
+            syntax_position,
+            function_context,
+        ))
     }
 
-    fn check_type(&self, source: &str, context: &Map) -> Result<()> {
+    fn check_type(&self, source: &str, _context: &Map) -> Result<()> {
         self.return_type()
-            .check(&self.body.expected_type(context)?)
+            .check(&self.body.expected_type(&self.context)?)
             .map_err(|error| error.at_source_position(source, self.syntax_position))?;
 
+        self.body.check_type(source, &self.context)?;
+
         Ok(())
     }
 
diff --git a/src/abstract_tree/identifier.rs b/src/abstract_tree/identifier.rs
index eec38f5..00194fc 100644
--- a/src/abstract_tree/identifier.rs
+++ b/src/abstract_tree/identifier.rs
@@ -39,19 +39,25 @@ impl AbstractTree for Identifier {
 
     fn run(&self, _source: &str, context: &Map) -> Result<Value> {
         if let Some((value, _)) = context.variables()?.get(&self.0) {
-            if !value.is_none() {
-                return Ok(value.clone());
-            }
+            Ok(value.clone())
+        } else {
+            Err(Error::VariableIdentifierNotFound(self.0.clone()))
         }
+    }
 
-        Err(Error::VariableIdentifierNotFound(self.0.clone()))
+    fn check_type(&self, _source: &str, context: &Map) -> Result<()> {
+        if let Some(_) = context.variables()?.get(&self.0) {
+            Ok(())
+        } else {
+            Err(Error::VariableIdentifierNotFound(self.0.clone()))
+        }
     }
 
     fn expected_type(&self, context: &Map) -> Result<Type> {
         if let Some((_value, r#type)) = context.variables()?.get(&self.0) {
             Ok(r#type.clone())
         } else {
-            Ok(Type::None)
+            Err(Error::VariableIdentifierNotFound(self.0.clone()))
         }
     }
 }
diff --git a/src/abstract_tree/value_node.rs b/src/abstract_tree/value_node.rs
index 0c742ff..e474a99 100644
--- a/src/abstract_tree/value_node.rs
+++ b/src/abstract_tree/value_node.rs
@@ -188,6 +188,27 @@ impl AbstractTree for ValueNode {
         Ok(value_node)
     }
 
+    fn check_type(&self, _source: &str, _context: &Map) -> Result<()> {
+        match self {
+            ValueNode::Boolean(_) => todo!(),
+            ValueNode::Float(_) => todo!(),
+            ValueNode::Function(function) => {
+                if let Function::ContextDefined(function_node) = function {
+                    function_node.check_type(_source, _context)?;
+                }
+            }
+            ValueNode::Integer(_) => todo!(),
+            ValueNode::String(_) => todo!(),
+            ValueNode::List(_) => todo!(),
+            ValueNode::Option(_) => todo!(),
+            ValueNode::Map(_) => todo!(),
+            ValueNode::BuiltInValue(_) => todo!(),
+            ValueNode::Structure(_) => todo!(),
+        }
+
+        Ok(())
+    }
+
     fn run(&self, source: &str, context: &Map) -> Result<Value> {
         let value = match self {
             ValueNode::Boolean(value_source) => Value::Boolean(value_source.parse().unwrap()),
diff --git a/src/value/map.rs b/src/value/map.rs
index 0102fc4..d0577ff 100644
--- a/src/value/map.rs
+++ b/src/value/map.rs
@@ -45,6 +45,17 @@ impl Map {
         })
     }
 
+    pub fn clone_complex_values_from(&self, other: &Self) -> Result<()> {
+        for (key, (value, r#type)) in other.variables()?.iter() {
+            if value.is_function() {
+                self.variables_mut()?
+                    .insert(key.clone(), (value.clone(), r#type.clone()));
+            }
+        }
+
+        Ok(())
+    }
+
     pub fn variables(&self) -> Result<RwLockReadGuard<BTreeMap<String, (Value, Type)>>> {
         Ok(self.variables.read()?)
     }