Boxed.hs

module Ref.Boxed where
import qualified Ref

type Ref = MutVar#

new :: a -> ST s (Ref s a)
new = newMutVar#

read :: Ref s a -> ST s a
read = readMutVar#

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

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

-- | Modify the contents of a @Ref.Boxed@, returning the previous contents and the result of applying the given function to the previous contents. Note that this isn't strictly speaking the correct type for this function; it should really be MutVar# s a -> (a -> (a,b)) -> State# s -> (# State# s, a, (a, b) #), but we don't know about pairs here.
-- 
-- Warning: this can fail with an unchecked exception.


modify :: Ref s a
       -> (a -> b)
       -> ST s (# a, b #) -- ^ Previous contents and the result of applying the function
modify r f s0 = case atomicModifyMutVar2# r f s0 of
  (# s1, old, new #) -> (# s1, (# old, new #) #)

modify_ :: Ref s a
        -> (a -> a)
        -> ST s (# a, a #) -- ^ Previous contents and the result of applying the function
modify_ r f s0 = case atomicModifyMutVar2# r f s0 of
  (# s1, old, new #) -> (# s1, (# old, new #) #)

cas :: Ref s a
    -> a -- ^ expected old value
    -> a -- ^ new value
    -> ST s (# B, a #) -- ^ Whether the swap failed, and the actual new value
cas r old new s0 = case casMutVar# r old new s0 of
  (# s1, failed', a #) -> (# s1, (# failed', a #) #)