all_match(is_alpha, "") ==> true.
all_match(is_alpha, "abc") ==> true.
all_match(is_alpha, "abc123") ==> false.
all_match(is_chess_piece, "♜♞♝♛♚♝♞♜") ==> true.
all_match(is_chess_piece, "♜♞♝♛K♝♞♜") ==> false.
all_match(is_alpha, "abc?def") ==> false.