+-- FIXME: doc
+data RFC1123
+
+instance ConvertSuccess ZonedTime (Tagged RFC1123 Ascii) where
+ {-# INLINE convertSuccess #-}
+ convertSuccess = (A.fromAsciiBuilder <$>) ∘ cs
+
+instance ConvertSuccess ZonedTime (Tagged RFC1123 AsciiBuilder) where
+ {-# INLINE convertSuccess #-}
+ convertSuccess = Tagged ∘ toAsciiBuilder
+
+instance ConvertAttempt (Tagged RFC1123 Ascii) ZonedTime where
+ {-# INLINE convertAttempt #-}
+ convertAttempt = parseAttempt' rfc1123DateAndTime ∘ untag
+
+-- |Parse an RFC 1123 date and time string.
+rfc1123DateAndTime ∷ Parser ZonedTime
+rfc1123DateAndTime = dateTime
+
+dateTime ∷ Parser ZonedTime
+dateTime = do weekDay ← optionMaybe $
+ do w ← shortWeekDayNameP
+ _ ← string ", "
+ return w
+ gregDay ← date
+ case weekDay of
+ Nothing
+ → return ()
+ Just givenWD
+ → assertWeekDayIsGood givenWD gregDay
+ (tod, timeZone) ← rfc822Time
+ let lt = LocalTime gregDay tod
+ zt = ZonedTime lt timeZone
+ return zt
+
+date ∷ Parser Day
+date = do day ← read2
+ _ ← char ' '
+ month ← shortMonthNameP
+ _ ← char ' '
+ year ← read4
+ _ ← char ' '
+ assertGregorianDateIsGood year month day
+
+toAsciiBuilder ∷ ZonedTime → AsciiBuilder
+toAsciiBuilder zonedTime