html-test/Operators: Clear up ambiguous types

For reasons that aren't entirely clear a class with ambiguous types was
accepted by GHC <8.0. I've added a functional dependency to clear up
this ambiguity.

1 files changed, 5 insertions, 1 deletions

diff --git a/html-test/src/Operators.hs b/html-test/src/Operators.hs
index f7b4d0ab..0b633c3f 100644
--- a/html-test/src/Operators.hs
+++ b/html-test/src/Operators.hs
@@ -1,4 +1,6 @@
 {-# LANGUAGE PatternSynonyms, TypeOperators, TypeFamilies, MultiParamTypeClasses, GADTs #-}
+{-# LANGUAGE FunctionalDependencies #-}
+
 -- | Test operators with or without fixity declarations
 module Operators where
 
@@ -42,7 +44,9 @@ data family a ** b
 infix 9 **
 
 -- | Class with fixity, including associated types
-class a ><> b where
+class a ><> b | a -> b where
+  -- Dec 2015: Added @a -> b@ functional dependency to clean up ambiguity
+  -- See GHC #11264
   type a <>< b :: *
   data a ><< b
   (>><), (<<>) :: a -> b -> ()