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 import Control.Monad
   9
  10 -- | = Yampa
  11
  12 countTo :: (Integral b) => b -> SF (Event a) (Event b)
  13 countTo n = count >>^ filterE (== n)
  14
  15 -- | Synchonizes two event sources. An event on the first source will be delayed until an event occurs on the second.
  16 --
  17 -- Ex:
  18 -- Event a => . . 1 . . . . 2 . . . 3 . . 4 . . . . . 5 . . 6 . . . . .
  19 -- Event b => . a . . . b . . . c . . . . . . d . e . f . . . . . g . .
  20 -- wairFor => . . . . . 1 . . . 2 . . . . . . 4 . . . 5 . . . . . 6 . .
  21
  22 waitForEvent :: SF (Event a, Event b) (Event a)
  23 waitForEvent = proc (ea,eb) -> do
  24   em <- arr $ uncurry $ mapMerge Left Right (\_ b -> Right b) -< (ea,eb)
  25   hob <- dAccumHoldBy accumulator NoEvent -< em
  26   returnA -< eb *> (ea `lMerge` hob)
  27   where accumulator :: Event a -> Either a b -> Event a
  28         accumulator _ (Left a) = Event a
  29         accumulator _ (Right _) = NoEvent
  30         --accumulator _ (Right b) =
  31
  32 {-
  33 waitForEvent :: SF (Event b, Event a) (Event b)
  34 waitForEvent = proc (eb,ea) -> do
  35   rec
  36     es' <- iPre NoEvent -< es
  37     es <- rSwitch waitAux -< ((eb,ea),es' `tag` waitAux)
  38   returnA -< es
  39   where waitAux = proc (eb,ea) -> do
  40           --ea' <- (if b then notYet else identity) -< ea
  41           eb' <- accumHoldBy (\_ b -> Event b) NoEvent -< eb
  42           returnA -< ea *> eb'
  43 -}
  44 -- | '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'.
  45 stepBack :: SF a (Maybe a)
  46 stepBack = sscan f (Nothing, Nothing) >>^ snd
  47   where f :: (Maybe a, Maybe a) -> a -> (Maybe a, Maybe a)
  48         f (Nothing,_) x' = (Just x', Nothing)
  49         f (Just x, _) x' = (Just x', Just x)
  50
  51 -- | Like 'stepBack' but the output value is always defined and is equal to the input at time 0.
  52 stepBack' :: SF a a
  53 stepBack' = proc x -> do
  54   x' <- stepBack -< x
  55   returnA -< fromMaybe x x'
  56
  57 -- | Throws an 'Event' when the incoming signal change. The 'Event' is tagged with the new value.
  58 onChange :: (Eq a) => SF a (Event a)
  59 onChange = proc x -> do
  60   x' <- stepBack -< x
  61   let makeEvent x x'
  62         | isNothing x' = NoEvent
  63         | otherwise = let x'' = fromJust x' in
  64             if x'' == x then NoEvent else Event x
  65   returnA -< makeEvent x x'
  66
  67 -- | Similar to 'onChange' but contains its initial value in the first
  68 -- event.
  69 onChange' :: (Eq a) => SF a (Event a)
  70 onChange' = proc x -> do
  71   x' <- stepBack -< x
  72   -- If it's the first value, throw an Event, else behave like onChange.
  73   let makeEvent x x'
  74         | isNothing x' = Event x
  75         | otherwise = let x'' = fromJust x' in
  76             if x'' == x then NoEvent else Event x
  77   returnA -< makeEvent x x'
  78
  79 -- | Integrates some variable modulo something.
  80 integralMod :: (Real a, VectorSpace a s) => a -> SF a a
  81 integralMod x = intMod' 0
  82   where intMod' x0 = switch (intMod'' x0) (\y -> intMod' (y - x))
  83         intMod'' x0 =  proc t -> do
  84           it <- (+ x0) ^<< integral -< t
  85           es <- edgeBy (\_ y -> guard (y > x) $> y) 0 -< it
  86           returnA -< (it,es)
  87
  88
  89
  90 -- | Generates a sine function whose period is given as a varying input.
  91 varFreqSine :: SF DTime Double
  92 varFreqSine = sin ^<< (2*pi*) ^<< integralMod 1 <<^ (1/)
  93
  94 -- | Generates an 'Event' with a regular period, which is given as an input to the signal function.
  95 repeatedlyS :: a -> SF DTime (Event a)
  96 repeatedlyS x = edgeBy (\a b -> guard (a * b < 0) $> x) 0
  97                 <<< varFreqSine <<^ (2*)
  98
  99 repeatedlyS' :: a -> SF DTime (Event a)
 100 repeatedlyS' x = (repeatedlyS x &&& now x) >>> arr (uncurry lMerge)
 101
 102 -- |
 103 -- = Curry and uncurry functions