diff --git a/src/lexer/char.rs b/src/lexer/char.rs
index 67534f3..3ef608f 100644
--- a/src/lexer/char.rs
+++ b/src/lexer/char.rs
@@ -9,15 +9,16 @@ pub trait Lexable {
     fn is_right_paren(&self) -> bool;
     fn is_identifier_initial(&self) -> bool;
     fn is_identifier_subsequent(&self) -> bool;
+    fn is_identifier_single(&self) -> bool;
 }
 
 impl Lexable for char {
     fn is_left_paren(&self) -> bool {
-        self == &'('
+        *self == '('
     }
 
     fn is_right_paren(&self) -> bool {
-        self == &')'
+        *self == ')'
     }
 
     fn is_identifier_initial(&self) -> bool {
@@ -27,5 +28,9 @@ impl Lexable for char {
     fn is_identifier_subsequent(&self) -> bool {
         charset::identifier_subsequents().contains(&self)
     }
+
+    fn is_identifier_single(&self) -> bool {
+        charset::identifier_singles().contains(&self)
+    }
 }
 
diff --git a/src/lexer/charset.rs b/src/lexer/charset.rs
index 63aaaaf..eb7e7cb 100644
--- a/src/lexer/charset.rs
+++ b/src/lexer/charset.rs
@@ -41,3 +41,7 @@ pub fn identifier_subsequents() -> CharSet {
     subsequents.extend(extras.iter());
     subsequents
 }
+
+pub fn identifier_singles() -> CharSet {
+    CharSet::from_iter("+-".chars())
+}
diff --git a/src/lexer/mod.rs b/src/lexer/mod.rs
index 5c61537..e64f5fa 100644
--- a/src/lexer/mod.rs
+++ b/src/lexer/mod.rs
@@ -76,6 +76,9 @@ impl Lexer {
         else if c.is_right_paren() {
             *token = Some(Token::new(Kind::RightParen, c.to_string()));
         }
+        else if c.is_identifier_single() {
+            *token = Some(Token::new(Kind::Identifier, c.to_string()));
+        }
         else if c.is_identifier_initial() {
             self.state = State::Identifier;
             self.advance();