Funcoes de data

function firstday returns date ( input dt as date ):
return ( if dt = ? then ? else date(month(dt),01,year(dt)) ).
end function.

function lastday returns date ( input dt as date ):
if dt = ? then return ( ? ).
else do:
dt = date(month(dt),28,year(dt)).
return ( dt + 4 - day(dt + 4) ).
end.
end function.