unsafe causes bug, news @ 11

I know there has been plenty of levity here lately but here goes :)

I didn't expect ‘isUndefined’ to be safe but this may be interesting to the devs (I am obedient and report it thusly and hereby-ly per GHC's request)

% ghci -ignore-dot-ghci
GHCi, version 8.1.20160117: http://www.haskell.org/ghc/  :? for help
Prelude> import Control.Exception
Prelude Control.Exception> import System.IO.Unsafe
Prelude Control.Exception System.IO.Unsafe> import Unsafe.Coerce
Prelude Control.Exception System.IO.Unsafe Unsafe.Coerce> isUndefined x = unsafePerformIO $ catch ((unsafeCoerce x :: IO ()) >> return False) (const $ return True :: SomeException -> IO Bool)
Prelude Control.Exception System.IO.Unsafe Unsafe.Coerce> isUndefined (succ True)
True
Prelude Control.Exception System.IO.Unsafe Unsafe.Coerce> isUndefined (succ False)
<interactive>: internal error: stg_ap_v_ret
    (GHC version 8.1.20160117 for x86_64_unknown_linux)
    Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug
Aborted (core dumped)
%

Trac metadata

Trac field	Value
Version	7.10.3
Type	Bug
TypeOfFailure	OtherFailure
Priority	normal
Resolution	Unresolved
Component	Compiler
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