Added custom prelude.

We need this again because of Monoid/Semigroup.

pandoc.cabal

@@ -398,6 +398,8 @@ library
                  http-client-tls >= 0.2.4 && < 0.4,
                  http-types >= 0.8 && < 0.13,
                  case-insensitive >= 1.2 && < 1.3
+  if !impl(ghc >= 8.0)
+    build-depends: semigroups == 0.18.*
   if os(windows)
     cpp-options:      -D_WINDOWS
   else
@@ -423,7 +425,7 @@ library
                       ScopedTypeVariables, GeneralizedNewtypeDeriving,
                       RelaxedPolyRec, DeriveDataTypeable, TypeSynonymInstances,
                       FlexibleInstances
-  hs-source-dirs:  src
+  hs-source-dirs:  src, prelude
 
   exposed-modules: Text.Pandoc,
                    Text.Pandoc.App,
@@ -508,7 +510,8 @@ library
                    Text.Pandoc.ImageSize,
                    Text.Pandoc.BCP47,
                    Text.Pandoc.Class
-  other-modules:   Text.Pandoc.Filter,
+  other-modules:   Prelude,
+                   Text.Pandoc.Filter,
                    Text.Pandoc.Filter.JSON,
                    Text.Pandoc.Filter.Lua,
                    Text.Pandoc.Filter.Path,
@@ -568,14 +571,16 @@ executable pandoc
                     ScopedTypeVariables, GeneralizedNewtypeDeriving,
                     RelaxedPolyRec, DeriveDataTypeable, TypeSynonymInstances,
                     FlexibleInstances
-  hs-source-dirs:  .
+  hs-source-dirs:  ., prelude
   main-is:         pandoc.hs
   buildable:       True
   other-modules:   Paths_pandoc
+                   Prelude
 
 executable trypandoc
   main-is:         trypandoc.hs
-  hs-source-dirs:  trypandoc
+  hs-source-dirs:  trypandoc, prelude
+  other-modules:   Prelude
   default-language: Haskell2010
   if flag(trypandoc)
     build-depends: base, aeson, pandoc,
@@ -586,7 +591,8 @@ executable trypandoc
 
 executable weigh-pandoc
   main-is:         weigh-pandoc.hs
-  hs-source-dirs:  benchmark
+  hs-source-dirs:  benchmark, prelude
+  other-modules: Prelude
   if flag(weigh-pandoc)
      build-depends:   pandoc,
                       base >= 4.2 && < 5,
@@ -602,7 +608,7 @@ executable weigh-pandoc
 test-suite test-pandoc
   type:           exitcode-stdio-1.0
   main-is:        test-pandoc.hs
-  hs-source-dirs: test
+  hs-source-dirs: test, prelude
   build-depends:  base >= 4.2 && < 5,
                   pandoc,
                   pandoc-types >= 1.17.4 && < 1.18,
@@ -631,7 +637,8 @@ test-suite test-pandoc
                     time >= 1.2 && < 1.5
   else
      build-depends: time >= 1.5 && < 1.10
-  other-modules:  Tests.Old
+  other-modules:  Prelude
+                  Tests.Old
                   Tests.Command
                   Tests.Helpers
                   Tests.Lua
@@ -684,7 +691,8 @@ test-suite test-pandoc
 benchmark benchmark-pandoc
   type:            exitcode-stdio-1.0
   main-is:         benchmark-pandoc.hs
-  hs-source-dirs:  benchmark
+  hs-source-dirs:  benchmark, prelude
+  other-modules:   Prelude
   build-depends:   pandoc,
                    time, bytestring, containers,
                    base >= 4.2 && < 5,

prelude/Prelude.hs

@@ -0,0 +1,22 @@
+{-# LANGUAGE PackageImports #-}
+{-# LANGUAGE CPP #-}
+
+module Prelude
+(
+  module P
+, Monoid(..)
+, Semigroup(..)
+, Applicative(..)
+#if MIN_VERSION_base(4,9,0)
+-- <> is exported in Semigroup
+#else
+, (<>)
+#endif
+)
+where
+
+import "base" Prelude as P
+import Data.Semigroup (Semigroup(..))  -- includes (<>)
+#if MIN_VERSION_base(4,11,0)
+import Data.Monoid (Monoid(..))
+#endif