mkWeakMVar is non-compositional
In base 4.6 addMVarFinalizer is deprecated in favour of mkWeakMVar of type
mkWeakMVar :: MVar a -> IO () -> IO (Weak (MVar a))This type makes it inherently non-compositional. For instance, if we have a larger datatype T that contains an MVar somewhere inside then there in no way to define mkWeakT in terms of mkWeakMVar; instead, mkWeakT would have to be defined along the lines of
mkWeakT :: T a -> IO () -> IO (Weak (T a))
mkWeakT m@(MkT (MVar m#) _) f = IO $ \s ->
case mkWeak# m# m f s of (# s1, w #) -> (# s1, Weak w #)It would be better if the type of mkWeakMVar would change to
mkWeakMVar :: MVar a -> v -> Maybe (IO ()) -> IO (Weak v)(i.e., following mkWeak rather than mkWeakPtr).
(The same comment goes for related functions such as mkWeakIORef.)
Trac metadata
| Trac field | Value |
|---|---|
| Version | 7.6.1 |
| Type | FeatureRequest |
| TypeOfFailure | OtherFailure |
| Priority | normal |
| Resolution | Unresolved |
| Component | Compiler |
| Test case | |
| Differential revisions | |
| BlockedBy | |
| Related | |
| Blocking | |
| CC | |
| Operating system | |
| Architecture |