Get rid of dodgy Show instance

GHC Head doesn't like it as it's overlapping, and in hindsight these
really shouldn't be there at all.

Leaving the non-wrapped version as it may be useful, but document
it (and the IO ones; leaving the IO-wrapped version in case people
use/rely upon it) that it's unsafe.

Author: ivan-m

Data/Graph/Inductive/Monad/IOArray.hs

@@ -46,9 +46,11 @@ showGraph (_,a,m) = concatMap showAdj (indices a)
                         Just (_,l,s) -> '\n':show v++":"++show l++"->"++show s'
                           where s' = unsafePerformIO (removeDel m s)
 
+-- | Please not that this instance is unsafe.
 instance (Show a,Show b) => Show (SGr a b) where
   show (SGr g) = showGraph g
 
+-- | Please not that this instance is unsafe.
 instance (Show a,Show b) => Show (IO (SGr a b)) where
   show g = unsafePerformIO (do {(SGr g') <- g; return (showGraph g')})
 

Data/Graph/Inductive/Monad/STArray.hs

@@ -50,12 +50,10 @@ showGraph (_,a,m) = concatMap showAdj (indices a)
 unsafeST :: ST RealWorld a -> a
 unsafeST = unsafePerformIO . stToIO
 
+-- | Please not that this instance is unsafe.
 instance (Show a,Show b) => Show (SGr RealWorld a b) where
   show (SGr g) = showGraph g
 
-instance (Show a,Show b) => Show (ST RealWorld (SGr RealWorld a b)) where
-  show g = unsafeST (do {(SGr g') <- g; return (showGraph g')})
-
 {-
 run :: Show (IO a) => IO a -> IO ()
 run x = seq x (print x)