Fixes for GHC 8.4.1 compatibility

* In GHC 8.4.1, the operator <> has become a method of the Semigroup class
  and is exported from the Prelude. This is unfortunate, since <> is also
  exported from the standard library module Text.PrettyPrint, so in any
  module that defines a pretty printer, there is likely to be an ambiguity.

  This affects ~18 modules in GF. Solution:

    import Prelude hiding (<>)

  This works also in older versions of GHC, since GHC does't complain if
  you hide something that doesn't exists.

* In GHC 8.4.1, Semigroup has become a superclass of Monoid. This means
  that anywhere you define an instance of the Monoid class you also have to
  define an instance in the Semigroup class.

  This affects Data.Binary.Builder in GF. Solution: conditionally define
  a Semigroup instance if compiling with base>=4.11 (ghc>=8.4.1)

2 files changed, 2 insertions, 0 deletions

diff --git a/src/compiler/GF/Infra/CheckM.hs b/src/compiler/GF/Infra/CheckM.hs
index 3b6833f0f..c5f9ba255 100644
--- a/src/compiler/GF/Infra/CheckM.hs
+++ b/src/compiler/GF/Infra/CheckM.hs
@@ -18,6 +18,7 @@ module GF.Infra.CheckM
 	   checkIn, checkInModule, checkMap, checkMapRecover,
            parallelCheck, accumulateError, commitCheck,
 	  ) where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 
 import GF.Data.Operations
 --import GF.Infra.Ident
diff --git a/src/compiler/GF/Infra/Location.hs b/src/compiler/GF/Infra/Location.hs
index 0bf85b37f..8447a297c 100644
--- a/src/compiler/GF/Infra/Location.hs
+++ b/src/compiler/GF/Infra/Location.hs
@@ -1,5 +1,6 @@
 -- | Source locations
 module GF.Infra.Location where
+import Prelude hiding ((<>)) -- GHC 8.4.1 clash with Text.PrettyPrint
 import GF.Text.Pretty
 
 -- ** Source locations