nom_combinators.rs

named!(single_token<&[u8], Token>,
    alt!(
        left_paren |
        right_paren |
        addition_sign |
        subtraction_sign |
        multiplication_sign |
        division_sign |
        operand
    )
);

named!(tokens<&[u8], Vec<Token>>,
    ws!(many0!(single_token))
);