diff --git a/dust-lang/src/built_in_functions.rs b/dust-lang/src/built_in_functions.rs
index 08dbf92..1d227d2 100644
--- a/dust-lang/src/built_in_functions.rs
+++ b/dust-lang/src/built_in_functions.rs
@@ -45,7 +45,7 @@ impl BuiltInFunction {
         }
     }
 
-    pub fn call(&self, arguments: Vec<Value>, context: &Context) -> Result<Action, RuntimeError> {
+    pub fn call(&self, arguments: Vec<Value>, _context: &Context) -> Result<Action, RuntimeError> {
         match self {
             // "INT_RANDOM_RANGE" => {
             //     let range = arguments.get(0).unwrap();
@@ -77,9 +77,6 @@ impl BuiltInFunction {
 
                 Ok(Action::None)
             }
-            _ => {
-                todo!()
-            }
         }
     }
 }
diff --git a/dust-lang/src/context.rs b/dust-lang/src/context.rs
index c23c984..979429b 100644
--- a/dust-lang/src/context.rs
+++ b/dust-lang/src/context.rs
@@ -14,6 +14,9 @@ pub fn std_context() -> Context {
     let mut interpreter = Interpreter::new(context.clone());
 
     interpreter.run(include_str!("../../std/io.ds")).unwrap();
+    interpreter
+        .run(include_str!("../../std/thread.ds"))
+        .unwrap();
 
     context
 }
diff --git a/dust-lang/src/error.rs b/dust-lang/src/error.rs
index d5fafc4..e13e085 100644
--- a/dust-lang/src/error.rs
+++ b/dust-lang/src/error.rs
@@ -1,6 +1,5 @@
-use std::{fmt::Debug, hash::Hash, io, ops::Range, sync::PoisonError};
+use std::{io, sync::PoisonError};
 
-use ariadne::{Color, Fmt, Label, Report, ReportKind};
 use chumsky::{prelude::Rich, span::Span};
 
 use crate::{
diff --git a/dust-shell/src/cli.rs b/dust-shell/src/cli.rs
index dd11449..450c3a0 100644
--- a/dust-shell/src/cli.rs
+++ b/dust-shell/src/cli.rs
@@ -1,10 +1,4 @@
-use std::{
-    borrow::Cow,
-    io::{stderr, Write},
-    path::PathBuf,
-    process::Command,
-    rc::Rc,
-};
+use std::{borrow::Cow, io::stderr, path::PathBuf, process::Command, rc::Rc};
 
 use ariadne::sources;
 use dust_lang::{
@@ -20,7 +14,7 @@ use reedline::{
 
 use crate::error::Error;
 
-pub fn run_shell(context: Context) {
+pub fn run_shell(context: Context) -> Result<(), Error> {
     let mut interpreter = Interpreter::new(context.clone());
     let mut keybindings = default_emacs_keybindings();
 
@@ -92,7 +86,7 @@ pub fn run_shell(context: Context) {
                     Err(errors) => {
                         let source_id = Rc::new("input".to_string());
                         let reports = Error::Dust { errors }
-                            .build_reports(source_id.clone(), &buffer)
+                            .build_reports(source_id.clone())
                             .unwrap();
 
                         for report in reports {
@@ -114,6 +108,8 @@ pub fn run_shell(context: Context) {
             }
         }
     }
+
+    Ok(())
 }
 
 struct StarshipPrompt {
diff --git a/dust-shell/src/error.rs b/dust-shell/src/error.rs
index eb3447b..4d74f17 100644
--- a/dust-shell/src/error.rs
+++ b/dust-shell/src/error.rs
@@ -1,14 +1,12 @@
 use ariadne::{Color, Fmt, Label, Report, ReportKind};
-use clap::error;
 use dust_lang::{
     abstract_tree::Type,
     error::{Error as DustError, RuntimeError, TypeConflict, ValidationError},
 };
 use std::{
-    fmt::{self, Debug, Display, Formatter},
+    fmt::{self, Display, Formatter},
     io,
     ops::Range,
-    path::Path,
     rc::Rc,
 };
 
@@ -20,11 +18,16 @@ pub enum Error {
     Io(io::Error),
 }
 
+impl From<io::Error> for Error {
+    fn from(error: io::Error) -> Self {
+        Error::Io(error)
+    }
+}
+
 impl Error {
     pub fn build_reports<'id>(
         self,
         source_id: Rc<String>,
-        source: &str,
     ) -> Result<Vec<Report<'id, (Rc<String>, Range<usize>)>>, io::Error> {
         if let Error::Dust { errors } = self {
             let mut reports = Vec::new();
@@ -241,3 +244,20 @@ impl Error {
         };
     }
 }
+
+impl Display for Error {
+    fn fmt(&self, f: &mut Formatter) -> fmt::Result {
+        match self {
+            Error::Dust { errors } => {
+                for error in errors {
+                    writeln!(f, "{error:?}")?;
+                }
+
+                Ok(())
+            }
+            Error::Io(io_error) => {
+                write!(f, "{io_error}")
+            }
+        }
+    }
+}
diff --git a/dust-shell/src/main.rs b/dust-shell/src/main.rs
index 4555440..33f7a73 100644
--- a/dust-shell/src/main.rs
+++ b/dust-shell/src/main.rs
@@ -11,7 +11,6 @@ use error::Error;
 use std::{
     fs::read_to_string,
     io::{stderr, Write},
-    path::Path,
     rc::Rc,
 };
 
@@ -47,7 +46,12 @@ fn main() {
     } else if let Some(command) = args.command {
         (command, Rc::new("input".to_string()))
     } else {
-        return run_shell(context);
+        match run_shell(context) {
+            Ok(_) => {}
+            Err(error) => eprintln!("{error}"),
+        }
+
+        return;
     };
 
     let eval_result = interpret(&source);
@@ -60,12 +64,25 @@ fn main() {
         }
         Err(errors) => {
             let reports = Error::Dust { errors }
-                .build_reports(source_id.clone(), &source)
+                .build_reports(source_id.clone())
                 .unwrap();
 
             for report in reports {
                 report
-                    .write_for_stdout(sources([(source_id.clone(), source.clone())]), stderr())
+                    .write_for_stdout(
+                        sources([
+                            (source_id.clone(), source.as_str()),
+                            (
+                                Rc::new("std/io.ds".to_string()),
+                                include_str!("../../std/io.ds"),
+                            ),
+                            (
+                                Rc::new("std/thread.ds".to_string()),
+                                include_str!("../../std/thread.ds"),
+                            ),
+                        ]),
+                        stderr(),
+                    )
                     .unwrap();
             }
         }
diff --git a/std/thread.ds b/std/thread.ds
index 2ef663e..1b1f80a 100644
--- a/std/thread.ds
+++ b/std/thread.ds
@@ -1,5 +1,5 @@
 thread = {
 	sleep = (milliseconds: int) : none {
-		__SLEEP__()
+		__SLEEP__(milliseconds)
 	}
 }