create a module to put all the compat necessary for running over a wide range of versions

Crypto/Hash/Internal.hs

@@ -1,24 +1,9 @@
-{-# LANGUAGE CPP #-}
-
 -- |
 -- Module      : Crypto.Hash.Internal
 -- License     : BSD-style
 -- Maintainer  : Vincent Hanquez <vincent@snarc.org>
 -- Stability   : experimental
 -- Portability : unknown
-module Crypto.Hash.Internal where
-
-import System.IO.Unsafe
-
--- | perform io for hashes that do allocation and ffi.
--- unsafeDupablePerformIO is used when possible as the
--- computation is pure and the output is directly linked
--- to the input. we also do not modify anything after it has
--- been returned to the user.
-unsafeDoIO :: IO a -> a
-#if __GLASGOW_HASKELL__ > 704
-unsafeDoIO = unsafeDupablePerformIO
-#else
-unsafeDoIO = unsafePerformIO
-#endif
+module Crypto.Hash.Internal (unsafeDoIO) where
 
+import Crypto.Internal.Compat (unsafeDoIO)

Crypto/Internal/Compat.hs

@@ -0,0 +1,28 @@
+-- |
+-- Module      : Crypto.Internal.Compat
+-- License     : BSD-style
+-- Maintainer  : Vincent Hanquez <vincent@snarc.org>
+-- Stability   : stable
+-- Portability : Good
+--
+-- This module try to keep all the difference between versions of base
+-- or other needed packages, so that modules don't need to use CPP
+--
+{-# LANGUAGE CPP #-}
+module Crypto.Internal.Compat
+    ( unsafeDoIO
+    ) where
+
+import System.IO.Unsafe
+
+-- | perform io for hashes that do allocation and ffi.
+-- unsafeDupablePerformIO is used when possible as the
+-- computation is pure and the output is directly linked
+-- to the input. we also do not modify anything after it has
+-- been returned to the user.
+unsafeDoIO :: IO a -> a
+#if __GLASGOW_HASKELL__ > 704
+unsafeDoIO = unsafeDupablePerformIO
+#else
+unsafeDoIO = unsafePerformIO
+#endif

cryptonite.cabal

@@ -58,6 +58,7 @@ Library
                    , Crypto.Hash.Types
                    , Crypto.Random.Entropy.Source
                    , Crypto.Random.Entropy.Backend
+                   , Crypto.Internal.Compat
   Build-depends:     base >= 4.5 && < 5
                    , bytestring
                    , securemem