snip.hs

getUpdatedUTC :: MonadMetadata m => TimeLocale -> Identifier -> m Clock.UTCTime
 getUpdatedUTC locale id' = do
     metadata <- getMetadata id'
     let tryField k fmt = lookupString k metadata >>= parseTime' fmt
     maybe empty' pure $ msum [tryField "updated" fmt | fmt <- formats]
   where
     empty' = fail $ "Hakyll.Web.Template.Context.getUpdatedUTC: " <> "could not parse time for " <> show id'
     parseTime' = parseTimeM True locale
     formats =
         [ "%a, %d %b %Y %H:%M:%S %Z"
         , "%Y-%m-%dT%H:%M:%S%Z"
         , "%Y-%m-%d %H:%M:%S%Z"
         , "%Y-%m-%d"
         , "%B %e, %Y %l:%M %p"
         , "%B %e, %Y"
         , "%b %d, %Y"
         ]

    • Could not deduce (MonadFail m) arising from a use of ‘fail’
      from the context: MonadMetadata m
        bound by the type signature for:
                   getUpdatedUTC :: forall (m :: * -> *).
                                    MonadMetadata m =>
                                    TimeLocale -> Identifier -> m UTCTime
        at src/site.hs:534:1-79
      Possible fix:
        add (MonadFail m) to the context of
          the inferred type of empty' :: m a
          or the type signature for:
               getUpdatedUTC :: forall (m :: * -> *).
                                MonadMetadata m =>
                                TimeLocale -> Identifier -> m UTCTime
    • In the expression:
        fail
          $ "Hakyll.Web.Template.Context.getUpdatedUTC: "
              ++ "could not parse time for " ++ show id'
      In an equation for ‘empty'’:
          empty'
            = fail
                $ "Hakyll.Web.Template.Context.getUpdatedUTC: "
                    ++ "could not parse time for " ++ show id'
      In an equation for ‘getUpdatedUTC’:
          getUpdatedUTC locale id'
            = do metadata <- getMetadata id'
                 let tryField k fmt = ...
                 maybe empty' return
                   $ msum [tryField "updated" fmt | fmt <- formats]
            where
                empty'
                  = fail
                      $ "Hakyll.Web.Template.Context.getUpdatedUTC: "
                          ++ "could not parse time for " ++ show id'
                parseTime' = parseTimeM True locale
                formats = ["%a, %d %b %Y %H:%M:%S %Z", ....]
    |
540 |     empty'     = fail $ "Hakyll.Web.Template.Context.getUpdatedUTC: " ++ "could not parse time for " ++ show id'
    |                  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^