Wall of fmaps - Haskell

Sridhar Ratnakumar

2020-11-14 22:58:48

hlint is not happy

with good reason!

it just wants to replace the last fmap with <$>

Georgi Lyubenov // googleson78

2020-11-14 23:02:55

why not

fmap fmap fmap fmap fmap fmap fmap fmap fmap fmap fmap

instead

Georgi Lyubenov // googleson78

2020-11-14 23:03:35

what is the thing being nested so deeply, is this in an instance declaration?

Sridhar Ratnakumar

2020-11-14 23:11:50

It is from ka.srid.ca, which is not open source yet. Attaching the code with context. Basically it calls all the plugins, and accumulates their results, uniformly. Since the plugin API is not finalized, and is stil in flux, I left the code un-refactored for now ...

  renderE <-
    mergeWith (flip Map.union)
      <$> sequence
        -- TODO: Eventually create a proper Plugin type to hold these functions.
        [ (fmap . fmap . fmap . fmap . fmap . fmap) (\x -> ThingVal_Pandoc :=> Identity x) $ pure pandocWithScopeE,
          (fmap . fmap . fmap . fmap . fmap) (\x -> (currTime, ThingVal_Calendar :=> Identity x)) $ Calendar.runPlugin graphD pandocD pandocWithScopeE,
          (fmap . fmap . fmap . fmap . fmap) (\x -> (currTime, ThingVal_Tasks :=> Identity x)) $ Task.runPlugin graphD pandocD pandocWithScopeE
        ]

image.png

Sridhar Ratnakumar

2020-11-14 23:12:47

The types are reflex events and dynamics, which look like:

m (Dynamic t (Map ThingName (ThingScope, (UTCTime, Pandoc))))

Sridhar Ratnakumar

2020-11-14 23:13:34

The calendar plugin (second line) for example is defined like:

runPlugin ::
  forall t m.
  ( Reflex t,
    MonadHold t m,
    MonadFix m,
    DomBuilder t m
  ) =>
  Dynamic t Graph ->
  Dynamic t (Map ThingName (ThingScope, (UTCTime, Pandoc))) ->
  Event t (Map ThingName (Maybe (ThingScope, (UTCTime, Pandoc)))) ->
  m (Event t (Map ThingName (Maybe (ThingScope, Set Day))))