Drop flag mtl1. Our lowest GHC, 7.6, already comes with mtl-2.

Author: andreasabel

HTTP.cabal

@@ -66,10 +66,6 @@ Source-Repository head
   type: git
   location: https://github.com/haskell/HTTP.git
 
-Flag mtl1
-  description: Use the old mtl version 1.
-  default: False
-
 Flag warn-as-error
   default:     False
   description: Build with warnings-as-errors
@@ -123,18 +119,12 @@ Library
         -- transformers-0.2.0.0 is the first to have Control.Monad.IO.Class
     -- The following dependencies are refined by flags, but they should
     -- still be mentioned here on the top-level.
-    , mtl           >= 1.1.1.0   && < 2.3
+    , mtl           >= 2.0.0.0   && < 2.3
     , network       >= 2.4       && < 3.2
 
   default-language: Haskell98
   default-extensions: FlexibleInstances
 
-  if flag(mtl1)
-    Build-depends: mtl < 1.2
-    CPP-Options: -DMTL1
-  else
-    Build-depends: mtl >= 2.0
-
   if flag(network-uri)
     Build-depends: network-uri == 2.6.*, network >= 2.6
   else

Network/Browser.hs

@@ -143,11 +143,7 @@ import Data.Maybe (fromMaybe, listToMaybe, catMaybes )
 #if !MIN_VERSION_base(4,8,0)
 import Control.Applicative (Applicative (..), (<$>))
 #endif
-#ifdef MTL1
-import Control.Monad (filterM, forM_, when, ap)
-#else
 import Control.Monad (filterM, forM_, when)
-#endif
 import Control.Monad.IO.Class
    ( MonadIO (..) )
 import Control.Monad.State
@@ -423,20 +419,12 @@ instance Show (BrowserState t) where
 -- | @BrowserAction@ is the IO monad, but carrying along a 'BrowserState'.
 newtype BrowserAction conn a
  = BA { unBA :: StateT (BrowserState conn) IO a }
-#ifdef MTL1
- deriving (Functor, Monad, MonadIO, MonadState (BrowserState conn))
-
-instance Applicative (BrowserAction conn) where
-  pure  = return
-  (<*>) = ap
-#else
  deriving
  ( Functor, Applicative, Monad, MonadIO, MonadState (BrowserState conn)
 #if MIN_VERSION_base(4,9,0)
  , MonadFail
 #endif
  )
-#endif
 
 runBA :: BrowserState conn -> BrowserAction conn a -> IO a
 runBA bs = flip evalStateT bs . unBA