Using cabal MIN_VERSION for transformers

Yesod.hs

@@ -35,7 +35,7 @@ import Yesod.Handler hiding (runHandler)
 import Network.Wai (Application)
 import Yesod.Hamlet
 import Data.Convertible.Text (cs)
-#if TRANSFORMERS_02
+#if MIN_VERSION_transformers(0,2,0)
 import "transformers" Control.Monad.IO.Class (liftIO)
 #else
 import "transformers" Control.Monad.Trans (liftIO)

Yesod/Form.hs

@@ -27,7 +27,7 @@ import Data.Time (Day)
 import Data.Convertible.Text
 import Control.Monad.Attempt
 import Data.Maybe (fromMaybe)
-#if TRANSFORMERS_02
+#if MIN_VERSION_transformers(0,2,0)
 import "transformers" Control.Monad.IO.Class
 #else
 import "transformers" Control.Monad.Trans

Yesod/Handler.hs

@@ -58,7 +58,7 @@ import Web.Mime
 import Control.Exception hiding (Handler)
 import Control.Applicative
 
-#if TRANSFORMERS_02
+#if MIN_VERSION_transformers(0,2,0)
 import "transformers" Control.Monad.IO.Class
 #else
 import "transformers" Control.Monad.Trans

Yesod/Request.hs

@@ -38,7 +38,7 @@ import qualified Network.Wai as W
 import Yesod.Definitions
 import Web.Encodings
 import qualified Data.ByteString.Lazy as BL
-#if TRANSFORMERS_02
+#if MIN_VERSION_transformers(0,2,0)
 import "transformers" Control.Monad.IO.Class
 #else
 import "transformers" Control.Monad.Trans

yesod.cabal

@@ -11,8 +11,6 @@ cabal-version:   >= 1.6
 build-type:      Simple
 homepage:        http://docs.yesodweb.com/yesod/
 
-flag transformers_02
-    description: transformers = 0.2.*
 flag buildtests
   description: Build the executable to run unit tests
   default: False
@@ -33,12 +31,8 @@ library
                      template-haskell,
                      web-routes >= 0.22 && < 0.23,
                      web-routes-quasi >= 0.1 && < 0.2,
-                     hamlet >= 0.0.1 && < 0.1
-    if flag(transformers_02)
-      build-depends: transformers >= 0.2 && < 0.3
-      CPP-OPTIONS: -DTRANSFORMERS_02
-    else
-      build-depends: transformers >= 0.1 && < 0.2
+                     hamlet >= 0.0.1 && < 0.1,
+                     transformers >= 0.1 && < 0.3
     exposed-modules: Yesod
                      Yesod.Content
                      Yesod.Definitions
@@ -68,11 +62,6 @@ executable             runtests
                        QuickCheck >= 2 && < 3
     else
         Buildable: False
-    if flag(transformers_02)
-      build-depends: transformers >= 0.2 && < 0.3
-      CPP-OPTIONS: -DTRANSFORMERS_02
-    else
-      build-depends: transformers >= 0.1 && < 0.2
     ghc-options:     -Wall
     main-is:         runtests.hs