New approach to custom Prelude.

We use no custom Prelude with the latest ghc version (8.4.1),
so we don't have problems with ghci.

See https://ghc.haskell.org/trac/ghc/ticket/10920
https://www.reddit.com/r/haskell/comments/3ryf2p/how_can_you_use_a_custom_prelude_with_ghci/

This may help with #4464.

pandoc.cabal

@@ -11,7 +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
+tested-with:     GHC == 7.10.3, GHC == 8.0.2, GHC == 8.2.2, GHC == 8.4.1
 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
@@ -398,8 +398,12 @@ 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)
+  if impl(ghc < 8.0)
     build-depends: semigroups == 0.18.*
+  if impl(ghc < 8.4)
+     hs-source-dirs: prelude
+     other-modules:  Prelude
+     build-depends:  base-compat >= 0.9
   if os(windows)
     cpp-options:      -D_WINDOWS
   else
@@ -563,8 +567,12 @@ library
 
 executable pandoc
   build-depends: pandoc, base >= 4.7 && < 5
-  if !impl(ghc >= 8.0)
+  if impl(ghc < 8.0)
     build-depends: semigroups == 0.18.*
+  if impl(ghc < 8.4)
+     hs-source-dirs: prelude
+     other-modules:  Prelude
+     build-depends:  base-compat >= 0.9
   ghc-options:   -rtsopts -with-rtsopts=-K16m -Wall -fno-warn-unused-do-bind -threaded
   if flag(static)
     ld-options:     -static
@@ -590,8 +598,12 @@ executable trypandoc
     buildable:     True
   else
     buildable:     False
-  if !impl(ghc >= 8.0)
+  if impl(ghc < 8.0)
     build-depends: semigroups == 0.18.*
+  if impl(ghc < 8.4)
+     hs-source-dirs: prelude
+     other-modules:  Prelude
+     build-depends:  base-compat >= 0.9
 
 executable weigh-pandoc
   main-is:         weigh-pandoc.hs
@@ -606,8 +618,12 @@ executable weigh-pandoc
      buildable:       True
   else
     buildable:     False
-  if !impl(ghc >= 8.0)
+  if impl(ghc < 8.0)
     build-depends: semigroups == 0.18.*
+  if impl(ghc < 8.4)
+     hs-source-dirs: prelude
+     other-modules:  Prelude
+     build-depends:  base-compat >= 0.9
   ghc-options:   -rtsopts -Wall -fno-warn-unused-do-bind
   default-language: Haskell98
 
@@ -638,8 +654,12 @@ test-suite test-pandoc
                   zip-archive >= 0.2.3.4 && < 0.4,
                   xml >= 1.3.12 && < 1.4,
                   Glob >= 0.7 && < 0.10
-  if !impl(ghc >= 8.0)
+  if impl(ghc < 8.0)
     build-depends: semigroups == 0.18.*
+  if impl(ghc < 8.4)
+     hs-source-dirs: prelude
+     other-modules:  Prelude
+     build-depends:  base-compat >= 0.9
   if flag(old-locale)
      build-depends: old-locale >= 1 && < 1.1,
                     time >= 1.2 && < 1.5
@@ -706,7 +726,11 @@ benchmark benchmark-pandoc
                    base >= 4.2 && < 5,
                    text >= 0.11 && < 1.3,
                    criterion >= 1.0 && < 1.5
-  if !impl(ghc >= 8.0)
+  if impl(ghc < 8.0)
     build-depends: semigroups == 0.18.*
+  if impl(ghc < 8.4)
+     hs-source-dirs: prelude
+     other-modules:  Prelude
+     build-depends:  base-compat >= 0.9
   ghc-options:   -rtsopts -Wall -fno-warn-unused-do-bind
   default-language: Haskell98

prelude/Prelude.hs

@@ -1,17 +1,17 @@
+{-# LANGUAGE NoImplicitPrelude #-}
 {-# LANGUAGE PackageImports #-}
 {-# LANGUAGE CPP #-}
 
+-- The intent is that this Prelude provide the API of
+-- the base 4.11 Prelude in a way that is portable for
+-- all base versions.
+
 module Prelude
 (
-  module P
-, Monoid(..)
+  module Prelude.Compat
 , Semigroup(..)
-, Applicative(..)
 )
 where
 
-import "base" Prelude as P
+import Prelude.Compat
 import Data.Semigroup (Semigroup(..))  -- includes (<>)
-#if MIN_VERSION_base(4,11,0)
-import Data.Monoid (Monoid(..))
-#endif