Fix panic when input is empty string

README.md

@@ -91,9 +91,6 @@ It's pretty fast and scales well. In my case, it usually runs in under 0.1ms. Th
 
 To see how fast it is, you can pass the `--debug` flag in CLI, or the `debug` argument to `eval()`.
 
-## Errors
-cpc returns `Result`s with basic strings as errors. Just to be safe, you may want to handle panics (You can do that using `std::panic::catch_unwind`).
-
 ## Dev Instructions
 
 ### Get started

src/lexer.rs

@@ -21,6 +21,10 @@ pub const fn is_alphabetic_extended(input: &char) -> bool {
 /// Lex an input string and return a [`TokenVector`]
 pub fn lex(input: &str, allow_trailing_operators: bool, default_degree: Unit) -> Result<TokenVector, String> {
 
+  if input == "" {
+    return Err(format!("Input was empty"))
+  }
+
   let mut input = input.replace(",", ""); // ignore commas
   input = input.to_lowercase();