- -> let (_, _, correctWD) = toWeekDate gregDay
- in
- if correctWD == givenWD then
- return () -- Correct day in the week.
- else
- let (year, month, day) = toGregorian gregDay
- in
- fail $ concat [ "Gregorian day "
- , show year
- , "-"
- , show month
- , "-"
- , show day
- , " is "
- , longWeekDayName correctWD
- , ", not "
- , longWeekDayName givenWD
- ]