Macro checked_arithmetic

macro_rules! checked_arithmetic {
    ($x:ident $op:ident $y:ident $op_name:expr) => { ... };
    ($x:ident + $y:ident) => { ... };
    ($x:ident - $y:ident) => { ... };
    ($x:ident * $y:ident) => { ... };
    ($x:ident / $y:ident) => { ... };
}