syntax_data: {"ast_node_type":"impl","tokens":[{"end":78,"kind":"keyword","start":0,"text":"op:"}]}
source_snippet:         op: impl FnOnce(&mut Self) -> Result<EvaluationResult, OverflowError>,
context_before:         &mut self,
context_after:     ) -> Result<EvaluationResult, OverflowError> {