warning: unused `std::result::Result` that must be used
   --> mfm_machine/src/state_machine/mod.rs:136:9
    |
136 | /         self.tracker.as_mut().track(
137 | |             Index::new(next_state_index, state.label(), state.tags()),
138 | |             context.clone(),
139 | |         );
    | |_________^
    |
    = note: this `Result` may be an `Err` variant, which should be handled
    = note: `#[warn(unused_must_use)]` on by default
help: use `let _ = ...` to ignore the resulting value
    |
136 |         let _ = self.tracker.as_mut().track(
    |         +++++++

warning: struct `TrackerHistory` has a public `len` method, but no `is_empty` method
  --> mfm_machine/src/state_machine/tracker.rs:36:5
   |
36 |     pub fn len(&self) -> usize {
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#len_without_is_empty
   = note: `#[warn(clippy::len_without_is_empty)]` on by default

warning: you should consider adding a `Default` implementation for `TrackerHistory`
  --> mfm_machine/src/state_machine/tracker.rs:32:5
   |
32 | /     pub fn new() -> Self {
33 | |         TrackerHistory(Vec::new())
34 | |     }
   | |_____^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#new_without_default
   = note: `#[warn(clippy::new_without_default)]` on by default
help: try adding this
   |
31 + impl Default for TrackerHistory {
32 +     fn default() -> Self {
33 +         Self::new()
34 +     }
35 + }
   |

warning: `.map().collect()` can be replaced with `.try_for_each()`
  --> mfm_machine/src/state_machine/tracker.rs:18:9
   |
18 | /         self.0
19 | |             .iter()
20 | |             .map(|(history_id, index, _)| {
21 | |                 writeln!(
...  |
26 | |             })
27 | |             .collect()
   | |______________________^
   |
   = help: for further information visit https://rust-lang.github.io/rust-clippy/master/index.html#map_collect_result_unit
   = note: `#[warn(clippy::map_collect_result_unit)]` on by default
help: try
   |
18 ~         self.0
19 +             .iter().try_for_each(|(history_id, index, _)| {
20 +                 writeln!(
21 +                     f,
22 +                     "history_id ({}); index ({:?}); context (ptr)",
23 +                     history_id, index
24 +                 )
25 +             })
   |