Number separator _

src/lexer.rs

@@ -40,10 +40,20 @@ impl<'a> Lexer<'a> {
                     let mut sval = String::from(ch);
 
                     // Do as long as a next char exists and it is a numeric char
-                    while let Some('0'..='9') = self.peek() {
+                    while let Some(ch) = self.peek() {
                         // The next char is verified to be Some, so unwrap is safe
+                        match ch {
+                            // Underscore is a separator, so remove it but don't add to number
+                            '_' => {
+                                self.next().unwrap();
+                            }
+                            '0'..='9' => {
                                 sval.push(self.next().unwrap());
                             }
+                            // Next char is not a number, so stop and finish the number token
+                            _ => break
+                        }
+                    }
 
                     // TODO: We only added numeric chars to the string, but the conversion could still fail
                     tokens.push(Token::I64(sval.parse().unwrap()));