module Util where
import Control.Applicative
import FRP.Elerea.Legacy.Delayed
-- Lifted conditional.
ifS c s1 s2 = c >>= \b -> if b then s1 else s2
-- Override the first output of a signal.
initSignal x s = do
c <- stateful True (const (const False))
return $ ifS c (pure x) s
scanM 0 _ _ = return []
scanM n f m = do
x <- f m
xs <- scanM (n-1) f x
return (x:xs)
-- Optional delay. Should memo behave like this?
dmemo = flip transfer (const const)
-- Functions moved over from the old Experimental top module
infix 4 ==@, /=@, <@, <=@, >=@, >@
infixr 3 &&@
infixr 2 ||@
infix 2 -->
-- | The 'edge' transfer function takes a bool signal and emits
-- another bool signal that turns true only at the moment when there
-- is a rising edge on the input.
edge :: Signal p Bool -> SignalGen p (Signal p Bool)
edge b = delay True b >>= \db -> return $ (not <$> db) &&@ b
-- | The '-->' transfer function behaves as a latch on a 'Maybe'
-- input: it keeps its state when the input is 'Nothing', and replaces
-- it with the input otherwise.
(-->) :: a -- ^ Initial output
-> Signal p (Maybe a) -- ^ Maybe signal to latch on
-> SignalGen p (Signal p a)
x0 --> s = transfer x0 store s
where store _ Nothing x = x
store _ (Just x) _ = x
-- | Point-wise equality of two signals.
(==@) :: Eq a => Signal p a -> Signal p a -> Signal p Bool
(==@) = liftA2 (==)
-- | Point-wise inequality of two signals.
(/=@) :: Eq a => Signal p a -> Signal p a -> Signal p Bool
(/=@) = liftA2 (/=)
-- | Point-wise comparison of two signals.
(<@) :: Ord a => Signal p a -> Signal p a -> Signal p Bool
(<@) = liftA2 (<)
-- | Point-wise comparison of two signals.
(<=@) :: Ord a => Signal p a -> Signal p a -> Signal p Bool
(<=@) = liftA2 (<=)
-- | Point-wise comparison of two signals.
(>=@) :: Ord a => Signal p a -> Signal p a -> Signal p Bool
(>=@) = liftA2 (>=)
-- | Point-wise comparison of two signals.
(>@) :: Ord a => Signal p a -> Signal p a -> Signal p Bool
(>@) = liftA2 (>)
-- | Point-wise OR of two boolean signals.
(||@) :: Signal p Bool -> Signal p Bool -> Signal p Bool
s1 ||@ s2 = s1 >>= \b -> if b then return True else s2
-- | Point-wise AND of two boolean signals.
(&&@) :: Signal p Bool -> Signal p Bool -> Signal p Bool
s1 &&@ s2 = s1 >>= \b -> if b then s2 else return False