diff --git a/dust-lang/src/lib.rs b/dust-lang/src/lib.rs
index 19f7a43..37d1e3d 100644
--- a/dust-lang/src/lib.rs
+++ b/dust-lang/src/lib.rs
@@ -47,29 +47,34 @@ impl Interpreter {
     }
 
     /// Lexes the source code and returns a list of tokens.
-    pub fn lex<'src>(
+    pub fn lex<'id>(
         &self,
         source_id: Arc<str>,
-        source: &'src str,
-    ) -> Result<Vec<Token<'src>>, InterpreterError> {
-        let mut sources = self.sources.write().unwrap();
+        source: &'id Arc<str>,
+    ) -> Result<Vec<Token<'id>>, InterpreterError> {
+        self.sources
+            .write()
+            .unwrap()
+            .insert(source_id.clone(), source.clone());
 
-        sources.insert(source_id.clone(), Arc::from(source));
-
-        lex(source)
+        lex(source.as_ref())
             .map(|tokens| tokens.into_iter().map(|(token, _)| token).collect())
-            .map_err(|errors| InterpreterError { source_id, errors })
+            .map_err(|errors| InterpreterError {
+                source_id: source_id.clone(),
+                errors,
+            })
     }
 
     /// Parses the source code and returns an abstract syntax tree.
-    pub fn parse(
+    pub fn parse<'id>(
         &self,
         source_id: Arc<str>,
-        source: &str,
+        source: &'id Arc<str>,
     ) -> Result<AbstractTree, InterpreterError> {
-        let mut sources = self.sources.write().unwrap();
-
-        sources.insert(source_id.clone(), Arc::from(source));
+        self.sources
+            .write()
+            .unwrap()
+            .insert(source_id.clone(), source.clone());
 
         parse(&lex(source).map_err(|errors| InterpreterError {
             source_id: source_id.clone(),
diff --git a/dust-shell/src/main.rs b/dust-shell/src/main.rs
index 2e1a174..63f793e 100644
--- a/dust-shell/src/main.rs
+++ b/dust-shell/src/main.rs
@@ -75,7 +75,7 @@ fn main() {
     };
 
     if args.lex {
-        match interpreter.lex(source_id, source.as_ref()) {
+        match interpreter.lex(source_id, &source) {
             Ok(tokens) => println!("{tokens:?}"),
             Err(error) => {
                 for report in error.build_reports() {
@@ -95,7 +95,7 @@ fn main() {
     }
 
     if args.parse {
-        match interpreter.parse(source_id, source.as_ref()) {
+        match interpreter.parse(source_id, &source) {
             Ok(abstract_tree) => println!("{abstract_tree:?}"),
             Err(error) => {
                 for report in error.build_reports() {
@@ -110,7 +110,7 @@ fn main() {
     }
 
     if args.compile {
-        match interpreter.parse(source_id, source.as_ref()) {
+        match interpreter.parse(source_id, &source) {
             Ok(abstract_tree) => {
                 let ron = ron::to_string(&abstract_tree).unwrap();