diff --git a/Data/Aeson/AutoType/Plugin/Loader.hs b/Data/Aeson/AutoType/Plugin/Loader.hs
new file mode 100644
--- /dev/null
+++ b/Data/Aeson/AutoType/Plugin/Loader.hs
@@ -0,0 +1,47 @@
+{-# LANGUAGE ScopedTypeVariables #-}
+-- | Module implementing loading generic plugins using Hint.
+module Data.Aeson.AutoType.Plugin.Loader (
+    importPlugins
+  , main
+  ) where
+
+import           System.IO     ( hPutStrLn, stderr )
+import           System.Exit   ( exitFailure )
+import           Data.Typeable
+import           Control.Arrow ((&&&))
+import           Control.Monad
+import qualified Language.Haskell.Interpreter as Hint
+
+-- | Test script
+main :: IO ()
+main  = do result :: [[Int]] <- importPlugins "export" moduleNames
+           forM_ (zip moduleNames result) $ \(moduleName, exportVal) ->
+             putStrLn $ concat [moduleName, ": ", show exportVal, "\n"]
+  where
+    moduleNames = ["Plugin.hs"
+                  ,"Plugin2.hs"]
+
+-- | Fatal exit from the program
+fatal :: String -> IO a
+fatal msg = do
+  hPutStrLn stderr msg
+  exitFailure
+
+-- | Imports a set of plugin modules with the same "interface" value,
+-- and returns values exported as their interfaces.
+importPlugins ::   Typeable a =>
+                   String     -> -- ^ name exported from each module as an interface
+                  [String]    -> -- ^ list of plugin modules (given as either module paths or file paths)
+                   IO [a]        -- ^ Result is a list of exported objects in the order of module names
+importPlugins interfaceName pluginModules = do
+    result <- Hint.runInterpreter $ do
+      Hint.loadModules pluginModules
+      moduleNames <- Hint.getLoadedModules
+      Hint.setImportsQ $ ("Prelude", Nothing):map (id &&& Just) moduleNames
+      mapM getInterfaceVar moduleNames
+    case result of
+      Left  err   -> fatal $ "Cannot load plugins:\n" ++ show err
+      Right value -> return value
+  where
+    getInterfaceVar moduleName = Hint.interpret (moduleName ++ "." ++ interfaceName) Hint.as
+
diff --git a/Data/Aeson/AutoType/Plugin/Subtype.hs b/Data/Aeson/AutoType/Plugin/Subtype.hs
new file mode 100644
--- /dev/null
+++ b/Data/Aeson/AutoType/Plugin/Subtype.hs
@@ -0,0 +1,25 @@
+module Data.Aeson.AutoType.Plugin.Subtype (
+    SubtypePlugin (..)
+  , SubtypeDesc   (..)
+  ) where
+
+import Data.Aeson.AutoType.Type
+import Data.Aeson
+import Data.Dynamic
+
+-- | Hmm... this should be existential type?
+type TypeDesc = String
+
+data SubtypePlugin = SubtypePlugin {
+    detect :: [Value]  -> Maybe SubtypeDesc -- | Check whether a set of values belongs to this type family
+  , unify  :: SubtypeDesc -> SubtypeDesc -> Either SubtypeDesc Type
+  }
+
+-- | Description of a subtype
+data SubtypeDesc = SubtypeDesc {
+    subtypeName  :: String           -- | Code that is different for different type families
+  , subtypeClass :: Type
+  , reference    :: String -> String -- | Show type reference with a given name prefix
+  , declare      :: String           -- | Show type declaration
+  , typeInfo     :: Dynamic
+  }
diff --git a/GenerateJSONParser.hs b/GenerateJSONParser.hs
--- a/GenerateJSONParser.hs
+++ b/GenerateJSONParser.hs
@@ -74,6 +74,9 @@
   -- Read type from each file
   typeForEachFile  <- catMaybes <$> mapM extractTypeFromJSONFile inputFilenames
   -- Unify all input types
+  when (null typeForEachFile) $ do
+    report "No valid JSON input file..."
+    exitFailure
   let finalType = foldr1 unifyTypes typeForEachFile
   -- We split different dictionary labels to become different type trees (and thus different declarations.)
   let splitted = splitTypeByLabel "TopLevel" finalType
diff --git a/changelog.md b/changelog.md
--- a/changelog.md
+++ b/changelog.md
@@ -1,5 +1,13 @@
 Changelog
 =========
+    0.2.5.5  Mar 2015
+
+        * Relaxed upper bounds for lens 4.8.
+    
+   0.2.5.5  Mar 2015
+
+        * (Skipped this version number by mistake.)
+
     0.2.5.4  Dec 2014
 
         * Relaxed upper bounds for new lens.
diff --git a/json-autotype.cabal b/json-autotype.cabal
--- a/json-autotype.cabal
+++ b/json-autotype.cabal
@@ -1,6 +1,6 @@
 -- Build information for the package.
 name:                json-autotype
-version:             0.2.5.4
+version:             0.2.5.6
 synopsis:            Automatic type declaration for JSON input data
 description:         Generates datatype declarations with Aeson's "FromJSON" instances
                      from a set of example ".json" files.
@@ -26,7 +26,7 @@
 stability:           beta
 author:              Michal J. Gajda
 maintainer:          mjgajda@gmail.com
-copyright:           Copyright by Michal J. Gajda '2014
+copyright:           Copyright by Michal J. Gajda '2014-'2015
 category:            Web
 build-type:          Simple
 extra-source-files:  README.md changelog.md
@@ -45,6 +45,8 @@
                        Data.Aeson.AutoType.Pretty
                        Data.Aeson.AutoType.CodeGen
                        Data.Aeson.AutoType.Alternative
+                       Data.Aeson.AutoType.Plugin.Subtype
+                       Data.Aeson.AutoType.Plugin.Loader
   other-extensions:    TemplateHaskell,
                        ScopedTypeVariables,
                        OverloadedStrings,
@@ -63,8 +65,9 @@
                        containers           >=0.3  && <0.6,
                        filepath             >=1.3  && <1.4,
                        hashable             >=1.2  && <1.3,
+                       hint                 >=0.4  && <0.5,
                        hflags               >=0.4  && <0.5,
-                       lens                 >=4.1  && <4.8,
+                       lens                 >=4.1  && <4.9,
                        mtl                  >=2.1  && <2.3,
                        pretty               >=1.1  && <1.3,
                        process              >=1.2  && <1.4,