diff --git a/examples/clue_solver.ds b/examples/clue_solver.ds
index 256c500..57ed983 100644
--- a/examples/clue_solver.ds
+++ b/examples/clue_solver.ds
@@ -51,4 +51,3 @@ take_turn(cards 'Conservatory' 'Kitchen')
 take_turn(cards 'White' 'Kitchen')
 take_turn(cards 'Green' 'Kitchen')
 take_turn(cards 'Knife' 'Kitchen')
-
diff --git a/examples/fibonacci.ds b/examples/fibonacci.ds
index 7d47b8f..c9aed88 100644
--- a/examples/fibonacci.ds
+++ b/examples/fibonacci.ds
@@ -2,7 +2,7 @@ fib = (i <int>) <int> {
 	if i <= 1 {
 		1
 	} else {
-		fib(i - 1) + fib(i - 2)
+		self(i - 1) + self(i - 2)
 	}
 }
 
diff --git a/src/abstract_tree/function_node.rs b/src/abstract_tree/function_node.rs
index 6beea2b..abf82e7 100644
--- a/src/abstract_tree/function_node.rs
+++ b/src/abstract_tree/function_node.rs
@@ -1,4 +1,7 @@
-use std::fmt::{self, Display, Formatter};
+use std::{
+    fmt::{self, Display, Formatter},
+    sync::Arc,
+};
 
 use serde::{Deserialize, Serialize};
 
@@ -65,7 +68,7 @@ impl FunctionNode {
     pub fn call(&self, arguments: &[Value], source: &str, outer_context: &Map) -> Result<Value> {
         for (key, (value, r#type)) in outer_context.variables()?.iter() {
             if let Value::Function(Function::ContextDefined(function_node)) = value {
-                if self == function_node {
+                if self == function_node.as_ref() {
                     continue;
                 }
             }
@@ -154,7 +157,9 @@ impl AbstractTree for FunctionNode {
     }
 
     fn run(&self, _source: &str, _context: &Map) -> Result<Value> {
-        Ok(Value::Function(Function::ContextDefined(self.clone())))
+        Ok(Value::Function(Function::ContextDefined(Arc::new(
+            self.clone(),
+        ))))
     }
 
     fn expected_type(&self, _context: &Map) -> Result<Type> {
diff --git a/src/abstract_tree/value_node.rs b/src/abstract_tree/value_node.rs
index 59a3550..4b751d3 100644
--- a/src/abstract_tree/value_node.rs
+++ b/src/abstract_tree/value_node.rs
@@ -1,4 +1,4 @@
-use std::collections::BTreeMap;
+use std::{collections::BTreeMap, sync::Arc};
 
 use serde::{Deserialize, Serialize};
 
@@ -34,7 +34,7 @@ impl AbstractTree for ValueNode {
             "function" => {
                 let function_node = FunctionNode::from_syntax(child, source, context)?;
 
-                ValueNode::Function(Function::ContextDefined(function_node))
+                ValueNode::Function(Function::ContextDefined(Arc::new(function_node)))
             }
             "integer" => ValueNode::Integer(source[child.byte_range()].to_string()),
             "string" => {
diff --git a/src/value/function.rs b/src/value/function.rs
index 3ba2209..a2e4706 100644
--- a/src/value/function.rs
+++ b/src/value/function.rs
@@ -1,4 +1,7 @@
-use std::fmt::{self, Display, Formatter};
+use std::{
+    fmt::{self, Display, Formatter},
+    sync::Arc,
+};
 
 use serde::{Deserialize, Serialize};
 
@@ -7,7 +10,7 @@ use crate::{BuiltInFunction, Format, FunctionNode, Map, Result, Type, Value};
 #[derive(Debug, Clone, Serialize, Deserialize, PartialEq, Eq, PartialOrd, Ord)]
 pub enum Function {
     BuiltIn(BuiltInFunction),
-    ContextDefined(FunctionNode),
+    ContextDefined(Arc<FunctionNode>),
 }
 
 impl Function {
@@ -19,12 +22,12 @@ impl Function {
             Function::ContextDefined(function_node) => {
                 function_node.set(
                     "self".to_string(),
-                    Value::Function(Function::ContextDefined(FunctionNode::new(
+                    Value::Function(Function::ContextDefined(Arc::new(FunctionNode::new(
                         function_node.parameters().clone(),
                         function_node.body().clone(),
                         function_node.r#type().clone(),
                         *function_node.syntax_position(),
-                    ))),
+                    )))),
                 )?;
 
                 function_node.call(arguments, source, outer_context)