syntax_data: {"ast_node_type":"variable","tokens":[{"end":76,"kind":"keyword","start":0,"text":"let"}]}
source_snippet:         let mut transitions: Map<State, Transitions<R, T>> = Map::default();
context_before:         let start = mapped((Some(a.start), Some(b.start)));
context_after:         let empty_transitions = Transitions::default();