HLint Warning: Parse error:

[MathiasBartl]

HLint produces this output:
user@user-Laptop:~/Gsoc/ConcurrentHashTable/gitHubRepo/Concurrent_Datastructures/Data/HashTable$ hlint Concurrent.hs
Concurrent.hs:863:1: Warning: Parse error: Illegal instance declaration
Found:

instance DebugShow Mask where
debugShow mask = do bitsstr <- return $ showIntAtBase 2 intToDigit mask ""
return $ "Mask: " ++ bitsstr ++ "\n"

1 suggestion
on commit 12e8216

I think thats actually an error not an suggestion

[MathiasBartl]

Ok this is probably because HLint deactivates an language extension that I am using.
but:
hlint -XTypeSynonymInstances -XFlexibleInstances -XFlexibleContexts -XScopedTypeVariables Concurrent.hs
has the same result