Add ^ to all matchers and avoid infinite loop if there's no match

src/lexer.rs

 lazy_static! {
     static ref WHITESPACE_REGEX: Regex = Regex::new(r"\s").unwrap();
     static ref MATCHERS: Vec<Matcher> = vec![
-        Matcher::new(r#""(.*)""#, TokenType::String),
-        Matcher::new(r#"SELECT"#, TokenType::Select),
-        Matcher::new(r#"FROM"#, TokenType::From),
-        Matcher::new(r#"[a-z][a-zA-Z_\-]*"#, TokenType::Identfiier),
-        Matcher::new(r#"[0-9]+"#, TokenType::Number),
-        Matcher::new(r#"\*"#, TokenType::Star),
+        Matcher::new(r#"^"(.*)""#, TokenType::String),
+        Matcher::new(r#"^SELECT"#, TokenType::Select),
+        Matcher::new(r#"^FROM"#, TokenType::From),
+        Matcher::new(r#"^[a-z][a-zA-Z_\-]*"#, TokenType::Identfiier),
+        Matcher::new(r#"^[0-9]+"#, TokenType::Number),
+        Matcher::new(r#"^\*"#, TokenType::Star),
     ];
 }
 
             position += 1;
         }
 
+        let mut matched = false;
+
         for matcher in MATCHERS.iter() {
             if matcher.regex.is_match(&input[position..]) {
                 if let Some(m) = matcher.regex.captures_iter(&input[position..]).next() {
                     let value = if m.len() > 1 { &m[1] } else { &m[0] };
                     position += value.len();
+
                     if matcher.token_type == TokenType::String {
                         position += 2
                     };
+
                     tokens.push(Token::new(matcher.token_type, value));
                 }
 
+                matched = true;
                 break;
             }
         }
+
+        if !matched {
+            return Err(LexerError::new("Unrecognized sequence"));
+        }
     }
 
     Ok(tokens)
     fn it_scans_a_star() {
         assert_eq!(scan("*").unwrap(), vec![Token::new(TokenType::Star, "*")])
     }
+
+    #[test]
+    fn it_scans_a_whole_expression() {
+        assert_eq!(
+            scan("SELECT * FROM index").unwrap(),
+            vec![
+                Token::new(TokenType::Select, "SELECT"),
+                Token::new(TokenType::Star, "*"),
+                Token::new(TokenType::From, "FROM"),
+                Token::new(TokenType::Identfiier, "index"),
+            ]
+        )
+    }
 }