[Haskell-cafe] Parsing LocalTime from Unix seconds
Alexander V Vershilov
alexander.vershilov at gmail.com
Fri Sep 14 08:27:16 UTC 2018
The best way of answering such questions is to check the source code.
a nice way of doing that - click on 'Source' near the instance that
you are interested in:
And you'll see the implementation
instance ParseTime LocalTime where
buildTime l xs = LocalTime <$> (buildTime l xs) <*> (buildTime l xs)
That builds time from `Day` and `TimeOfDay` passing your parse string
to each of those.
Then you can check ParseTime instance of Day:
I'm not providing it here, as it's quite big, but the main point is
that `s` is ignored so in that case
Day appear to be:
rest (YearMonth m:_) = let
d = safeLast 1 [x | MonthDay x <- cs]
in fromGregorianValid y m d
if you continue the process for TimeOfDay you'll find that `s` is
ignored there as well, and
`midnight = TimeOfDay 0 0 0` is returned in that case.
So it appeared that LocalTime consists of the components that ignore
your parse string and return
default value instead.
I don't know if that is intended behaviour or not, but for me it makes
more sense to parse to UTCTime/POSIXTime
and then convert into LocalTime, in case if you get seconds as input.
Hope that helps.
On Thu, 6 Sep 2018 at 13:42, Marc Busqué <marc at lamarciana.com> wrote:
> In GHCi
> :m +Data.Time
> parseTimeM True defaultTimeLocale "%s" "1535684406" :: Maybe UTCTime
> -- => Just 2018-08-31 03:00:06 UTC
> parseTimeM True defaultTimeLocale "%s" "1535684406" :: Maybe LocalTime
> -- => Just 1970-01-01 00:00:00
> Why? ¯\(°_o)/¯
> Marc Busqué
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