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Use a more stack efficient version of mapM #6

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12 changes: 11 additions & 1 deletion Data/Time/LocalTime/TimeZone/Olson/Parse.hs
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Original file line number Diff line number Diff line change
Expand Up @@ -60,7 +60,7 @@ instance Exception OlsonError
-- | Convert parsed Olson timezone data into a @TimeZoneSeries@.
olsonToTimeZoneSeries :: OlsonData -> Maybe TimeZoneSeries
olsonToTimeZoneSeries (OlsonData ttimes ttinfos@(dflt0:_) _ _) =
fmap (TimeZoneSeries $ mkTZ dflt) . mapM (lookupTZ ttinfos) .
fmap (TimeZoneSeries $ mkTZ dflt) . mapMMaybe (lookupTZ ttinfos) .
uniqTimes . sortBy futureToPast $ ttimes
where
dflt = fromMaybe dflt0 . listToMaybe $ filter isStd ttinfos
Expand All @@ -74,6 +74,16 @@ olsonToTimeZoneSeries (OlsonData ttimes ttinfos@(dflt0:_) _ _) =
futureToPast = comparing $ negate . transTime
olsonToTimeZoneSeries _ = Nothing

mapMMaybe :: (a -> Maybe b) -> [a] -> Maybe [b]
mapMMaybe f ls = mapMCont f ls []

mapMCont :: (a -> Maybe b) -> [a] -> [b] -> Maybe [b]
mapMCont f [] acc = Just (reverse acc)
mapMCont f (x:xs) acc =
case f x of
Nothing -> Nothing
Just x -> mapMCont f xs (x:acc)

-- | Read timezone data from a binary Olson timezone file and convert
-- it into a @TimeZoneSeries@ for use together with the types and
-- fucntions of "Data.Time". This is the function from this module
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