Move DataBox into Utils.

AnyDataItem is effectively the same, so we could reuse DataBox for that
too in the future.

common/GenericUtils.hs

@@ -39,6 +39,7 @@ import Data.Typeable
 import System.IO.Unsafe
 
 import qualified AST as A
+import Utils
 
 -- | A type identifier.
 type TypeKey = Int
@@ -47,9 +48,6 @@ type TypeKey = Int
 typeKey :: Typeable a => a -> TypeKey
 typeKey x = unsafePerformIO $ typeRepKey $ typeOf x
 
--- | Container for 'Data' items.
-data DataBox = forall a. (Typeable a, Data a) => DataBox a
-
 -- | Given a witness for a type, return witnesses for all the types that its
 -- constructors take.
 constrArgTypes :: (Data a, Typeable a) => a -> [DataBox]

common/Utils.hs

@@ -23,6 +23,7 @@ module Utils where
 import Control.Monad.State
 import Data.Array.IArray
 import Data.List
+import Data.Generics (Data)
 import qualified Data.Map as Map
 import Data.Maybe
 import Data.Ord
@@ -296,3 +297,6 @@ makeArraySize size def arr = array size [(i,arrayLookupWithDefault def arr i) |
 -- This is like '(\/\/)'.
 replaceAt :: Int -> a -> [a] -> [a]
 replaceAt n rep es = [if i == n then rep else e | (e, i) <- zip es [0..]]
+
+-- | A type that can contain any 'Data' item.
+data DataBox = forall t. Data t => DataBox t