error[E0495]: cannot infer an appropriate lifetime for autoref due to conflicting requirements
  --> src/lexer.rs:81:18
   |
81 |         let ret = self.peek();
   |                        ^^^^
   |
note: first, the lifetime cannot outlive the anonymous lifetime #1 defined on the method body at 74:2...
  --> src/lexer.rs:74:2
   |
74 |       pub fn next(&mut self) -> &Token {
   |  _____^
75 | |         /*if self.index >= self.tokens.len() {
76 | |             return &Token::EOF;
77 | |         }
...  |
83 | |         return ret;
84 | |     }
   | |_____^
note: ...so that reference does not outlive borrowed content
  --> src/lexer.rs:81:13
   |
81 |         let ret = self.peek();
   |                   ^^^^
note: but, the lifetime must be valid for the lifetime 'a as defined on the impl at 66:6...
  --> src/lexer.rs:66:6
   |
66 | impl<'a> Lexer<'a> {
   |      ^^
   = note: ...so that the types are compatible:
           expected &mut lexer::Lexer<'_>
              found &mut lexer::Lexer<'a>