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Created February 10, 2015 22:31
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foldl.hs
countViewsFold :: (Hashable k, Eq k)
=> (Event -> Maybe k)
-> L.Fold Event (MonoidalHashMap k (Sum Integer))
countViewsFold keyF = L.Fold s mempty id
where
s m ev@(Event _ _ _ _ (ThresholdEvent _ _)) =
maybe m (\k -> M.modify (+1) k m) (keyF ev)
s m _ = m
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