🐛 Fix build on old compilers

Author: lsrcz

src/Grisette/Lib/Synth/Operator/OpParser.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GADTs #-}
 
 module Grisette.Lib.Synth.Operator.OpParser (OpParser (..)) where
 

src/Grisette/Lib/Synth/Program/ProgParser.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GADTs #-}
 
 module Grisette.Lib.Synth.Program.ProgParser
   ( ProgParser (..),

src/Grisette/Lib/Synth/Type/TypeParser.hs

@@ -1,4 +1,5 @@
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GADTs #-}
 
 module Grisette.Lib.Synth.Type.TypeParser (TypeParser (..)) where
 

src/Grisette/Lib/Synth/Util/Parser.hs

@@ -1,5 +1,6 @@
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE GADTs #-}
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE ScopedTypeVariables #-}