Function sexp_err_to_match_arg_err 

fn sexp_err_to_match_arg_err(e: SexpError) -> MatchArgError

Map a SexpError from a string TryFromSexp conversion into a MatchArgError.

Only Type and Length are produced by the &str/Option<&str>/ Vec<Option<&str>> conversions we delegate to — other variants are unreachable in this context.