Macro tt_is_comma 

macro_rules! tt_is_comma {
    {
        $caller:tt
        input = [{ , }]
    } => { ... };
    {
        $caller:tt
        input = [{ $other:tt }]
    } => { ... };
}

Predicate that accepts a single token and determines whether it is a comma. ^[tt-call]

Input

• input = [{ a single token tree }]

Output

• is_comma = [{ either true or false }]