restore import of liftA2 for compatibility with older GHC

Author: winitzki

dhall/src/Dhall/Import/Headers.hs

@@ -10,7 +10,7 @@ module Dhall.Import.Headers
     , toOriginHeaders
     ) where
 
-import Control.Applicative (Alternative (..))
+import Control.Applicative (Alternative (..), liftA2)
 import Control.Exception   (SomeException)
 import Control.Monad.Catch (handle, throwM)
 import Data.Text           (Text)

dhall/src/Dhall/Marshal/Decode.hs

@@ -136,7 +136,7 @@ module Dhall.Marshal.Decode
     ) where
 
 
-import Control.Applicative              (empty)
+import Control.Applicative              (empty, liftA2)
 import Control.Exception                (Exception)
 import Control.Monad                    (guard)
 import Control.Monad.Trans.State.Strict

dhall/src/Dhall/Parser/Combinators.hs

@@ -23,7 +23,7 @@ module Dhall.Parser.Combinators
     ) where
 
 
-import Control.Applicative     (Alternative (..))
+import Control.Applicative     (Alternative (..), liftA2)
 import Control.Exception       (Exception)
 import Control.Monad           (MonadPlus (..))
 import Data.String             (IsString (..))

dhall/src/Dhall/Parser/Expression.hs

@@ -8,7 +8,7 @@
 -- | Parsing Dhall expressions.
 module Dhall.Parser.Expression where
 
-import Control.Applicative     (Alternative (..), optional)
+import Control.Applicative     (Alternative (..), liftA2, optional)
 import Data.Foldable           (foldl')
 import Data.List.NonEmpty      (NonEmpty (..))
 import Data.Text               (Text)