Function weekday_of_first 

pub fn weekday_of_first(year: i32, month: u32) -> u32

Get the weekday of the first day of a Shahanshahi month. Returns 0=Saturday, 1=Sunday, …, 6=Friday (Iranian week).

Panics

Panics if the computed Gregorian date is invalid, which cannot happen for any valid Shahanshahi (year, month) since the 1st of every month maps to a real calendar date.