Hello, In my usb-safe[1] library I make extensive use of the ViewPatterns[2] language extension. However I get strange warnings when using them. See for example the following function: resetDevice ∷ (pr `ParentOf` cr, MonadIO cr) ⇒ RegionalDeviceHandle pr → cr () resetDevice (internalHandle → DeviceHandle { internalDevHndl , configAlreadySetMVar }) = ... where: type RegionalDeviceHandle r = RegionalHandle USB.Device r internalHandle ∷ RegionalHandle resource r → Handle resource and: 'Handle' is an associated data type with the following definition: data Handle USB.Device = DeviceHandle { internalDevHndl ∷ USB.DeviceHandle , configAlreadySetMVar ∷ MVar Bool } Note that I also use the NamedFieldPuns[3] language extension. When compiling the module I get lots of warnings like this: System/USB/Safe.hs:372:0: Warning: Pattern match(es) are overlapped In the definition of `resetDevice': resetDevice ((internalHandle -> (DeviceHandle {internalDevHndl, configAlreadySetMVar}))) = ... System/USB/Safe.hs:372:0: Warning: Pattern match(es) are non-exhaustive In the definition of `resetDevice': Patterns not matched: I don't understand which patterns are overlapped or which patterns are not matched. Is this a GHC bug? Note that I'm using ghc-6.10.4 so it's possible that it's fixed in 6.12.1. regards, Bas [1] usb-safe: http://hackage.haskell.org/package/usb-safe-0.4 or darcs get http://code.haskell.org/~basvandijk/code/usb-safe [2] http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#vi... [3] http://www.haskell.org/ghc/docs/latest/html/users_guide/syntax-extns.html#re...