Add Free module.

postlude.cabal

@@ -20,6 +20,7 @@ library
   build-depends:       base >= 4.7 && < 5,
                        bytestring == 0.10.8.1,
                        either == 4.4.1.1,
+                       free == 4.12.4,
                        mtl == 2.2.1,
                        text == 1.2.2.2,
                        transformers == 0.5.5.0

src/Postlude.hs

@@ -39,6 +39,12 @@ import Control.Monad.Except as X
   ( ExceptT, ExceptT(ExceptT), runExceptT
   )
 
+import Control.Monad.Free as X
+  ( Free, Free(Pure), Free(Free)
+  , retract
+  , wrap
+  )
+
 import Control.Monad.Reader as X
   ( MonadReader, ask, local, reader
   , Reader, runReader