Adds support for exponential notation

src/lex.rs

@@ -263,10 +263,27 @@ pub(crate) fn lexer(input: &str, prev_ans: Option<f64>) -> Result<Vec<Token>, Ca
             }
             'a'..='z' | 'A'..='Z' => {
                 let parse_num = num_vec.parse::<f64>().ok();
+
                 if let Some(x) = parse_num {
+                    num_vec.clear();
+
+                    // Check for exponential notation
+                    if letter == 'e' {
+                        while let Some(next) = chars.next_if(|&x| matches!(x, '0'..='9')) {
+                            num_vec.push(next);
+                        }
+
+                        if !num_vec.is_empty() {
+                            if let Some(exp) = num_vec.parse::<usize>().ok() {
+                                result.push(Token::Num(x * num::pow(10 as f64, exp) as f64));
+                                num_vec.clear();
+                                continue;
+                            }
+                        }
+                    }
+
                     result.push(Token::Num(x));
                     result.push(OPERATORS.get(&'*').unwrap().clone());
-                    num_vec.clear();
                 }
                 char_vec.push(letter);
                 last_char_is_op = false;

src/lib.rs

@@ -145,6 +145,17 @@ mod tests {
         let evaled = eval("exp(3)", None);
         assert_eq!(evaled, Ok(20.0855369232));
     }
+    #[test]
+    fn eval_exponential_notation() {
+        let evaled = eval("1e11", None);
+        assert_eq!(evaled, Ok(100000000000.0));
+    }
+    #[test]
+    fn eval_exponential_notation_decimal() {
+        let evaled = eval("2.5e5", None);
+        assert_eq!(evaled, Ok(250000.0));
+    }
+
     #[test]
     fn eval_e_times_n() {
         let evaled = eval("e0", None);