Improve error handling for Eat optional parameter

renrs/src/lib.rs

@@ -140,6 +140,11 @@ fn parse_file(file_path: PathBuf) -> Vec<Command> {
     let token_lines = tokenize_file(file_path);
     let mut commands = Vec::new();
     for line in token_lines {
+        macro_rules! unknown {
+            () => {
+                panic!("Unknown command {}", describe_line(&line))
+            };
+        }
         commands.push(match line.as_slice() {
             [Str(text)] => Say {
                 name: None,
@@ -153,10 +158,10 @@ fn parse_file(file_path: PathBuf) -> Vec<Command> {
                 food: food.to_owned(),
                 politely: match tail {
                     [Boolean(politely)] => *politely,
-                    _ => false,
+                    _ => unknown!(),
                 },
             },
-            _ => panic!("Unknown command {}", describe_line(&line)),
+            _ => unknown!(),
         });
     }
     commands