src/RMCA/Auxiliary/Yampa.hs

   1 {-# LANGUAGE Arrows #-}
   2
   3 module RMCA.Auxiliary.Yampa where
   4
   5 import FRP.Yampa
   6 import Data.Maybe
   7 import RMCA.Auxiliary.Misc
   8
   9 -- | = Yampa
  10
  11 countTo :: (Integral b) => b -> SF (Event a) (Event b)
  12 countTo n = count >>^ filterE (== n)
  13
  14 -- | Synchonizes two event sources. An event on the first source will be delayed until an event occurs on the second.
  15 --
  16 -- Ex:
  17 -- Event a => . . 1 . . . . 2 . . . 3 . . 4 . . . . . 5 . . 6 . . . . .
  18 -- Event b => . a . . . b . . . c . . . . . . d . e . f . . . . . g . .
  19 -- wairFor => . . . . . 1 . . . 2 . . . . . . 4 . . . 5 . . . . . 6 . .
  20
  21 -- A more direct approach, and without any use of *> to avoid depending
  22 -- on applicatives.
  23
  24 waitForEvent :: SF (Event a, Event b) (Event a)
  25 waitForEvent = sscanPrim procEvts NoEvent NoEvent
  26     where
  27         procEvts eaPrev (NoEvent,      NoEvent) = Just (eaPrev,  NoEvent)
  28         procEvts _      (ea@(Event _), NoEvent) = Just (ea,      NoEvent)
  29         procEvts eaPrev (NoEvent,      Event _) = Just (NoEvent, eaPrev)
  30         procEvts _      (ea@(Event _), Event _) = Just (NoEvent, ea)
  31
  32 {-
  33 waitForEvent :: SF (Event a, Event b) (Event a)
  34 waitForEvent = proc (ea,eb) -> do
  35   em <- arr $ uncurry $ mapMerge Left Right (\_ b -> Right b) -< (ea,eb)
  36   hob <- dAccumHoldBy accumulator NoEvent -< em
  37   returnA -< eb *> (ea `lMerge` hob)
  38   where accumulator :: Event a -> Either a b -> Event a
  39         accumulator _ (Left a) = Event a
  40         accumulator _ (Right _) = NoEvent
  41         --accumulator _ (Right b) =
  42 -}
  43
  44 {-
  45 waitForEvent :: SF (Event b, Event a) (Event b)
  46 waitForEvent = proc (eb,ea) -> do
  47   rec
  48     es' <- iPre NoEvent -< es
  49     es <- rSwitch waitAux -< ((eb,ea),es' `tag` waitAux)
  50   returnA -< es
  51   where waitAux = proc (eb,ea) -> do
  52           --ea' <- (if b then notYet else identity) -< ea
  53           eb' <- accumHoldBy (\_ b -> Event b) NoEvent -< eb
  54           returnA -< ea *> eb'
  55 -}
  56 -- | 'stepBack' contains its previous argument as its output. Because it's hard to define it at time 0, it's wrapped up in a 'Maybe'.
  57 stepBack :: SF a (Maybe a)
  58 stepBack = sscan f (Nothing, Nothing) >>^ snd
  59   where f :: (Maybe a, Maybe a) -> a -> (Maybe a, Maybe a)
  60         f (Nothing,_) x' = (Just x', Nothing)
  61         f (Just x, _) x' = (Just x', Just x)
  62
  63 -- | Like 'stepBack' but the output value is always defined and is equal to the input at time 0.
  64 stepBack' :: SF a a
  65 stepBack' = proc x -> do
  66   x' <- stepBack -< x
  67   returnA -< fromMaybe x x'
  68
  69 -- | Throws an 'Event' when the incoming signal change. The 'Event' is tagged with the new value.
  70 onChange :: (Eq a) => SF a (Event a)
  71 onChange = proc x -> do
  72   x' <- stepBack -< x
  73   let makeEvent x x'
  74         | isNothing x' = NoEvent
  75         | otherwise = let x'' = fromJust x' in
  76             if x'' == x then NoEvent else Event x
  77   returnA -< makeEvent x x'
  78
  79 -- | Similar to 'onChange' but contains its initial value in the first
  80 -- event.
  81 onChange' :: (Eq a) => SF a (Event a)
  82 onChange' = proc x -> do
  83   x' <- stepBack -< x
  84   -- If it's the first value, throw an Event, else behave like onChange.
  85   let makeEvent x x'
  86         | isNothing x' = Event x
  87         | otherwise = let x'' = fromJust x' in
  88             if x'' == x then NoEvent else Event x
  89   returnA -< makeEvent x x'
  90
  91 -- | Integrates some variable modulo something.
  92 integralMod :: (Real a, VectorSpace a s) => a -> SF a a
  93 integralMod x = intMod' 0
  94   where intMod' x0 = switch (intMod'' x0) (\y -> intMod' (y - x))
  95         intMod'' x0 =  proc t -> do
  96           it <- (+ x0) ^<< integral -< t
  97           es <- edgeBy (\_ y -> if y > x then Just y else Nothing) 0 -< it
  98           returnA -< (it,es)
  99
 100
 101
 102 -- | Generates a sine function whose period is given as a varying input.
 103 varFreqSine :: SF DTime Double
 104 varFreqSine = sin ^<< (2*pi*) ^<< integralMod 1 <<^ (1/)
 105
 106 -- | Generates an 'Event' with a regular period, which is given as an input to the signal function.
 107 repeatedlyS :: a -> SF DTime (Event a)
 108 repeatedlyS x = edgeBy (\a b -> if a * b < 0 then Just x else Nothing) 0
 109                 <<< varFreqSine <<^ (2*)
 110
 111 repeatedlyS' :: a -> SF DTime (Event a)
 112 repeatedlyS' x = (repeatedlyS x &&& now x) >>> arr (uncurry lMerge)
 113
 114 -- |
 115 -- = Curry and uncurry functions