diff --git a/src/interpreter/callable.rs b/src/interpreter/callable.rs
index 26a8390..695f300 100644
--- a/src/interpreter/callable.rs
+++ b/src/interpreter/callable.rs
@@ -1,4 +1,4 @@
-use std::fmt::Debug;
+use std::{cell::RefCell, fmt::Debug, rc::Rc};
 
 use crate::errors::InterpreterError;
 
@@ -17,3 +17,6 @@ pub trait Callable: Debug + ToString {
         arguments: Vec<Value>,
     ) -> Result<Value, InterpreterError>;
 }
+
+/// A reference to a callable.
+pub type CallableRef = Rc<RefCell<dyn Callable>>;
diff --git a/src/interpreter/mod.rs b/src/interpreter/mod.rs
index 4041801..d6ed7a1 100644
--- a/src/interpreter/mod.rs
+++ b/src/interpreter/mod.rs
@@ -4,7 +4,7 @@ mod interpretable;
 mod native_fn;
 mod value;
 
-pub use callable::Callable;
+pub use callable::{Callable, CallableRef};
 pub use environment::*;
 pub use interpretable::*;
 pub use value::*;