Upsample.hs

{-# LANGUAGE RecordWildCards #-}
{-# LANGUAGE TypeFamilies #-}

{- | Utilities to run 'ClSF's at the speed of combined clocks
   when they are defined only for a constituent clock.
-}
module FRP.Rhine.ClSF.Upsample where

-- dunai
import Control.Monad.Trans.MSF.Reader

-- rhine
import FRP.Rhine.ClSF.Core
import FRP.Rhine.Clock
import FRP.Rhine.Schedule

{- | An 'MSF' can be given arbitrary other arguments
   that cause it to tick without doing anything
   and replicating the last output.
-}
upsampleMSF :: Monad m => b -> MSF m a b -> MSF m (Either arbitrary a) b
upsampleMSF b msf = right msf >>> accumulateWith (<>) (Right b) >>> arr fromRight
  where
    fromRight (Right b') = b'
    fromRight (Left _) = error "fromRight: This case never occurs in upsampleMSF."

-- Note that the Semigroup instance of Either a arbitrary
-- updates when the first argument is Right.

{- | Upsample a 'ClSF' to a parallel clock.
   The given 'ClSF' is only called when @clR@ ticks,
   otherwise the last output is replicated
   (with the given @b@ as initialisation).
-}
upsampleR ::
  (Monad m, Time clL ~ Time clR) =>
  b ->
  ClSF m clR a b ->
  ClSF m (ParallelClock m clL clR) a b
upsampleR b clsf = readerS $ arr remap >>> upsampleMSF b (runReaderS clsf)
  where
    remap (TimeInfo {tag = Left tag}, _) = Left tag
    remap (TimeInfo {tag = Right tag, ..}, a) = Right (TimeInfo {..}, a)

{- | Upsample a 'ClSF' to a parallel clock.
   The given 'ClSF' is only called when @clL@ ticks,
   otherwise the last output is replicated
   (with the given @b@ as initialisation).
-}
upsampleL ::
  (Monad m, Time clL ~ Time clR) =>
  b ->
  ClSF m clL a b ->
  ClSF m (ParallelClock m clL clR) a b
upsampleL b clsf = readerS $ arr remap >>> upsampleMSF b (runReaderS clsf)
  where
    remap (TimeInfo {tag = Right tag}, _) = Left tag
    remap (TimeInfo {tag = Left tag, ..}, a) = Right (TimeInfo {..}, a)