module Ref.Lock where

type Ref = MVar#

eq :: Ref s a -> Ref s a -> B
eq = sameMVar#

empty' :: Ref s a -> ST s B
empty' = isEmptyMVar#

-- | A new empty @Ref@
new :: ST s (Ref s a)
new = newMVar#

-- | Block until the @Ref@ is full/unlocked, then atomically take the value and lock it.
take :: Ref s a -> ST s a
take = takeMVar#

-- | Take the current value if it exists and lock the @Ref@
take' :: Ref s a -> ST s (Maybe# a) {- ^ The value if the @Ref@ was full/unlocked -}
take' r s0 = case tryTakeMVar# r s0 of
  (# s1, full', a #) -> (# s1, (# full', a #) #)

-- | Block until the @Ref@ is full/unlocked, then read the value but don't lock it.
read :: Ref s a -> ST s a
read = readMVar#

-- | Take the current value if it exists but don't lock the @Ref@
read' :: Ref s a -> ST s (Maybe# a) {- ^ The value if the @Ref@ was full/unlocked -}
read' r s0 = case tryReadMVar# r s0 of
  (# s1, full', a #) -> (# s1, (# full', a #) #)

write :: Ref s a -> a -> ST_ s
write = putMVar#

write' :: Ref s a -> a -> ST s B {- ^ whether the write succeeded -}
write' = tryPutMVar#