error[E0596]: cannot borrow immutable field `self.feeds` as mutable
   --> src/world.rs:110:46
    |
81  |     pub fn replay(self, filenames: Vec<&str>) -> Result<(), String> {
    |                   ---- consider changing this to `mut self`
...
110 |                     let book_handler = &mut (self.feeds[filehead.book_index].0);
    |                                              ^^^^^^^^^^ cannot mutably borrow immutable field

error: aborting due to previous error

error: Could not compile `numisma`.