diff --git a/rust/src/compiler.rs b/rust/src/compiler.rs
index f5a4130..8f81807 100644
--- a/rust/src/compiler.rs
+++ b/rust/src/compiler.rs
@@ -1,4 +1,4 @@
-use crate::scanner::{Scanner, TokenKind};
+use crate::scanner::Scanner;
 use color_eyre::eyre::Result;
 
 pub fn compile(source: &str) -> Result<()> {
diff --git a/rust/src/scanner.rs b/rust/src/scanner.rs
index f0fdc18..abfe0d3 100644
--- a/rust/src/scanner.rs
+++ b/rust/src/scanner.rs
@@ -4,6 +4,10 @@ pub struct Scanner<'a> {
     line: usize,
 }
 
+fn is_alpha(c: char) -> bool {
+    c.is_ascii_alphabetic() || c == '_'
+}
+
 impl<'a> Scanner<'a> {
     pub fn new(source: &'a str) -> Self {
         Self {
@@ -13,22 +17,6 @@ impl<'a> Scanner<'a> {
         }
     }
 
-    fn make_token(&self, kind: TokenKind) -> Token<'a> {
-        Token {
-            kind,
-            value: std::str::from_utf8(&self.source[..self.current]).unwrap(),
-            line: self.line,
-        }
-    }
-
-    fn error_token(&self, message: &'static str) -> Token<'a> {
-        Token {
-            kind: TokenKind::Error,
-            value: message,
-            line: self.line,
-        }
-    }
-
     fn advance(&mut self) -> char {
         self.current += 1;
         self.source[self.current - 1] as char
@@ -75,7 +63,7 @@ impl<'a> Scanner<'a> {
         self.source.get(self.current).map(|&x| x as char)
     }
 
-    fn peek_next(&mut self) -> Option<char> {
+    fn peek_next(&self) -> Option<char> {
         self.source.get(self.current + 1).map(|&x| x as char)
     }
 
@@ -89,11 +77,11 @@ impl<'a> Scanner<'a> {
 
         if self.peek().is_none() {
             // Maybe this should return an Err?
-            return self.error_token("Unterminated string.");
+            return Token::error(&self, "Unterminated string.");
         }
 
         self.advance();
-        self.make_token(TokenKind::String)
+        Token::new(self, TokenKind::String)
     }
 
     fn number(&mut self) -> Token<'a> {
@@ -109,7 +97,7 @@ impl<'a> Scanner<'a> {
             }
         }
 
-        self.make_token(TokenKind::Number)
+        Token::new(self, TokenKind::Number)
     }
 
     fn identifier(&mut self) -> Token<'a> {
@@ -117,7 +105,7 @@ impl<'a> Scanner<'a> {
             self.advance();
         }
 
-        self.make_token(self.identifier_type())
+        Token::new(self, self.identifier_type())
     }
 
     fn identifier_type(&self) -> TokenKind {
@@ -154,66 +142,83 @@ impl<'a> Iterator for Scanner<'a> {
 
     fn next(&mut self) -> Option<Self::Item> {
         self.skip_whitespace();
-        self.peek()?;
+
+        if self.peek().is_none() {
+            return Some(Token::new(self, TokenKind::Eof));
+        }
 
         Some(match self.advance() {
             c if is_alpha(c) => self.identifier(),
             c if c.is_ascii_digit() => self.number(),
-            '(' => self.make_token(TokenKind::LeftParen),
-            ')' => self.make_token(TokenKind::RightParen),
-            '{' => self.make_token(TokenKind::LeftBrace),
-            '}' => self.make_token(TokenKind::RightBrace),
-            ';' => self.make_token(TokenKind::Semicolon),
-            ',' => self.make_token(TokenKind::Comma),
-            '.' => self.make_token(TokenKind::Dot),
-            '-' => self.make_token(TokenKind::Minus),
-            '+' => self.make_token(TokenKind::Plus),
-            '/' => self.make_token(TokenKind::Slash),
-            '*' => self.make_token(TokenKind::Star),
+            '(' => Token::new(self, TokenKind::LeftParen),
+            ')' => Token::new(self, TokenKind::RightParen),
+            '{' => Token::new(self, TokenKind::LeftBrace),
+            '}' => Token::new(self, TokenKind::RightBrace),
+            ';' => Token::new(self, TokenKind::Semicolon),
+            ',' => Token::new(self, TokenKind::Comma),
+            '.' => Token::new(self, TokenKind::Dot),
+            '-' => Token::new(self, TokenKind::Minus),
+            '+' => Token::new(self, TokenKind::Plus),
+            '/' => Token::new(self, TokenKind::Slash),
+            '*' => Token::new(self, TokenKind::Star),
             '!' => {
                 if self.is_match('=') {
-                    self.make_token(TokenKind::BangEqual)
+                    Token::new(self, TokenKind::BangEqual)
                 } else {
-                    self.make_token(TokenKind::Bang)
+                    Token::new(self, TokenKind::Bang)
                 }
             }
             '=' => {
                 if self.is_match('=') {
-                    self.make_token(TokenKind::EqualEqual)
+                    Token::new(self, TokenKind::EqualEqual)
                 } else {
-                    self.make_token(TokenKind::Equal)
+                    Token::new(self, TokenKind::Equal)
                 }
             }
             '<' => {
                 if self.is_match('=') {
-                    self.make_token(TokenKind::LessEqual)
+                    Token::new(self, TokenKind::LessEqual)
                 } else {
-                    self.make_token(TokenKind::Less)
+                    Token::new(self, TokenKind::Less)
                 }
             }
             '>' => {
                 if self.is_match('=') {
-                    self.make_token(TokenKind::GreaterEqual)
+                    Token::new(self, TokenKind::GreaterEqual)
                 } else {
-                    self.make_token(TokenKind::Greater)
+                    Token::new(self, TokenKind::Greater)
                 }
             }
             '"' => self.string(),
-            _ => self.error_token("Unexpected character."),
+            _ => Token::error(self, "Unexpected character."),
         })
     }
 }
 
-fn is_alpha(c: char) -> bool {
-    c.is_ascii_alphabetic() || c == '_'
-}
-
 pub struct Token<'a> {
     pub kind: TokenKind,
     pub value: &'a str,
     pub line: usize,
 }
 
+impl<'a> Token<'a> {
+    fn new(scanner: &Scanner<'a>, kind: TokenKind) -> Self {
+        Token {
+            kind,
+            value: std::str::from_utf8(&scanner.source[..scanner.current]).unwrap(),
+            line: scanner.line,
+        }
+    }
+
+    fn error(scanner: &Scanner, message: &'static str) -> Self {
+        Token {
+            kind: TokenKind::Error,
+            value: message,
+            line: scanner.line,
+        }
+    }
+}
+
 #[derive(Debug, PartialEq)]
 pub enum TokenKind {
     // Single-character tokens.
@@ -293,7 +298,7 @@ mod tests {
         assert_source_scan("fa", Some(TokenKind::Identifier));
 
         assert_source_scan("@", Some(TokenKind::Error));
-        assert_source_scan("", None);
+        assert_source_scan("", Some(TokenKind::Eof));
     }
 
     #[test]
@@ -301,14 +306,14 @@ mod tests {
         let mut scanner = Scanner::new("()");
         assert_scan(&mut scanner, Some(TokenKind::LeftParen));
         assert_scan(&mut scanner, Some(TokenKind::RightParen));
-        assert_scan(&mut scanner, None);
+        assert_scan(&mut scanner, Some(TokenKind::Eof));
     }
 
     #[test]
     fn test_whitespace() {
         assert_source_scan(" foo", Some(TokenKind::Identifier));
         assert_source_scan("\tfoo", Some(TokenKind::Identifier));
-        assert_source_scan("//   \n", None);
+        assert_source_scan("//   \n", Some(TokenKind::Eof));
     }
 
     fn assert_source_scan(source: &str, kind: Option<TokenKind>) {