Hi Artur (and everybody who's interested), I'm trying to leverage your calendar-related package and have some questions, especially about the function date_to_iso8601. First of all, it would be useful if the doc explained a little bit more what's actually supported. Internally the function uses the built-in strptime and so on, so maybe it would be enough to refer to gretl's function reference for that. Then, I'm observing that the result for date_to_iso8601("1984", "%Y") is: 19831231. Is this a bug? I would have expected 19840101. Next, my feature request would be to support other date specifications used by gretl as well, such as for quarterly data things like "1974:3". (It does work with such monthly specifications, apart from an apparent bug similar to the one above.)  I'm aware that quarterly data isn't covered by ISO8601. At the end of this message is a code proposal on how to deal with such quarterly labels. Your date_to_iso8601 function could perhaps allow a "Q" code in the date_format argument and do something like this: if instring(toupper(date_format), "Q")     scalar iso8601 = gretlquarter_to_iso8601(date) else ... < existing part of your function> endif What do you think? thanks sven ------ <hansl> function scalar gretlquarter_to_iso8601(string date)     # This function only supports quarterly date strings     # as used and accepted by gretl itself;     # basically only patterns like "1999:3" or "1999.3".     errorif(!instring(date, ":") && !instring(date, "."), \       "not a recognized quarterly date string")     # harmonize and check     date = strstrip(strsub(date, ".", ":"))     strings parts = strsplit(date, ":")     errorif(nelem(parts) != 2, "invalid date string input")     # convert (and check)     year    = atof(parts[1])     quarter = atof(parts[2])     errorif(year < 1000 || year > 9999, "year out of range")     errorif(quarter < 1 || quarter > 4, "quarter out of range")     # construct the ISO output     out  = year * 10000                    # year     out += ((quarter-1) * 3 + 1) * 100    # first month in quarter     out += 1                            # first day in month     return out end function # some tests eval gretlquarter_to_iso8601("2004:4") eval gretlquarter_to_iso8601("20000:1")    # wrong eval gretlquarter_to_iso8601("2000-3")    # also wrong eval gretlquarter_to_iso8601("1901:12")    # wrong eval gretlquarter_to_iso8601("1900:3") </hansl>