diff --git a/src/interpreter/callable.rs b/src/interpreter/callable.rs
index c82922d..ab55270 100644
--- a/src/interpreter/callable.rs
+++ b/src/interpreter/callable.rs
@@ -1,5 +1,11 @@
+use std::fmt::Debug;
+
+use crate::errors::InterpreterError;
+
+use super::{Environment, Value};
+
 /// A callable is some object that supports being called.
-pub trait Callable {
+pub trait Callable: Debug + ToString {
     /// Return the amount of arguments supported by the callable.
     fn arity(&self) -> usize;