Drop support for ghc < 8.

CONTRIBUTING.md

@@ -144,7 +144,7 @@ Please follow these guidelines:
 9.  It is better not to introduce new dependencies.  Dependencies on
     external C libraries should especially be avoided.
 
-10. We aim for compatibility with ghc versions from 7.10.3 to the
+10. We aim for compatibility with ghc versions from 8.0 to the
     latest release.  All pull requests and commits are tested
     automatically on CircleCI.
 

pandoc.cabal

@@ -11,8 +11,7 @@ bug-reports:     https://github.com/jgm/pandoc/issues
 stability:       alpha
 homepage:        https://pandoc.org
 category:        Text
-tested-with:     GHC == 7.10.3, GHC == 8.0.2, GHC == 8.2.2, GHC == 8.4.4,
-                 GHC == 8.6.3
+tested-with:     GHC == 8.0.2, GHC == 8.2.2, GHC == 8.4.4, GHC == 8.6.3
 synopsis:        Conversion between markup formats
 description:     Pandoc is a Haskell library for converting from one markup
                  format to another, and a command-line tool that uses

src/Text/Pandoc/Class.hs

@@ -9,10 +9,6 @@
 {-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE UndecidableInstances #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-#if MIN_VERSION_base(4,8,0)
-#else
-{-# LANGUAGE OverlappingInstances #-}
-#endif
 {- |
    Module      : Text.Pandoc.Class
    Copyright   : Copyright (C) 2016-17 Jesse Rosenthal, John MacFarlane
@@ -1041,11 +1037,7 @@ instance (MonadTrans t, PandocMonad m, Functor (t m),
   putCommonState = lift . putCommonState
   logOutput = lift . logOutput
 
-#if MIN_VERSION_base(4,8,0)
 instance {-# OVERLAPS #-} PandocMonad m => PandocMonad (ParsecT s st m) where
-#else
-instance PandocMonad m => PandocMonad (ParsecT s st m) where
-#endif
   lookupEnv = lift . lookupEnv
   getCurrentTime = lift getCurrentTime
   getCurrentTimeZone = lift getCurrentTimeZone

src/Text/Pandoc/PDF.hs

@@ -34,11 +34,7 @@ import System.FilePath
 import System.IO (stdout)
 import System.IO.Temp (withSystemTempDirectory, withTempDirectory,
                        withTempFile)
-#if MIN_VERSION_base(4,8,3)
 import System.IO.Error (IOError, isDoesNotExistError)
-#else
-import System.IO.Error (isDoesNotExistError)
-#endif
 import Text.Pandoc.Definition
 import Text.Pandoc.Error (PandocError (PandocPDFProgramNotFoundError))
 import Text.Pandoc.MIME (getMimeType)

src/Text/Pandoc/Readers/Docx.hs

@@ -79,9 +79,6 @@ import Text.Pandoc.Readers.Docx.Parse
 import Text.Pandoc.Shared
 import Text.Pandoc.Walk
 import Text.TeXMath (writeTeX)
-#if !(MIN_VERSION_base(4,8,0))
-import Data.Traversable (traverse)
-#endif
 import Control.Monad.Except (throwError)
 import Text.Pandoc.Class (PandocMonad)
 import qualified Text.Pandoc.Class as P