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Following the existing functions mkWeakIORef and mkWeakMVar, I'd like to have a function mkWeakChan with the following type signature, similar to that of mkWeakMVar requested by ticket #7285:

mkWeakChan :: Chan a -> v -> Maybe (IO ()) -> IO (Weak v)

The implementation of Chan is private, so it is not easily possible to implement it yourself. The implementation of both functions may look like the following:

mkWeakMVar :: MVar a -> v -> Maybe (IO ()) -> IO (Weak v)
mkWeakMVar (MVar m#) v (Just f) = IO $ \s ->
  case mkWeak# m# v f s of (# s1, w #) -> (# s1, Weak w #)
mkWeakMVar (MVar m#) v Nothing  = IO $ \s ->
  case mkWeakNoFinalizer# m# v s of { (# s1, w #) -> (# s1, Weak w #) }

mkWeakChan :: Chan a -> v -> Maybe (IO ()) -> IO (Weak v)
mkWeakChan c@(Chan readVar writeVar) v f = do
  _ <- mkWeakMVar readVar  writeVar Nothing
  mkWeakMVar writeVar v f

Trac metadata

Trac field	Value
Version	7.6.3
Type	FeatureRequest
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	libraries/base
Test case
Differential revisions
BlockedBy
Related	#7285
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Operating system
Architecture