Function match_arg_vec_into_sexp 

pub fn match_arg_vec_into_sexp<T: MatchArg>(values: Vec<T>) -> SEXP

Convert a Vec<T: MatchArg> to an R character vector (STRSXP).

Each element is written as its canonical choice string via MatchArg::to_choice. Empty choice strings are stored as R_BlankString (parity with choices_sexp).

Called by the impl IntoR for Vec<T> block emitted by #[derive(MatchArg)].