Added explicit fixity to (~).

Solves #18252

2 files changed, 11 insertions, 0 deletions

diff --git a/libraries/ghc-prim/GHC/Types.hs b/libraries/ghc-prim/GHC/Types.hs
index 5198a486e4..2883e3b04c 100644
--- a/libraries/ghc-prim/GHC/Types.hs
+++ b/libraries/ghc-prim/GHC/Types.hs
@@ -256,13 +256,20 @@ inside GHC, to change the kind and type.
 -- about the difference between heterogeneous equality @~~@ and
 -- homogeneous equality @~@, this is printed as @~@ unless
 -- @-fprint-equality-relations@ is set.
+--
+-- In @0.7.0@, the fixity was set to @infix 4@ to match the fixity of 'Data.Type.Equality.:~~:'.
 class a ~~ b
+
   -- See also Note [The equality types story] in GHC.Builtin.Types.Prim
 
 -- | Lifted, homogeneous equality. By lifted, we mean that it
 -- can be bogus (deferred type error). By homogeneous, the two
 -- types @a@ and @b@ must have the same kinds.
+
+-- In @0.7.0@, the fixity was set to @infix 4@ to match the fixity of 'Data.Type.Equality.:~:'.
 class a ~ b
+
+infix 4 ~, ~~
   -- See also Note [The equality types story] in GHC.Builtin.Types.Prim
 
 -- | @Coercible@ is a two-parameter class that has instances for types @a@ and @b@ if
diff --git a/libraries/ghc-prim/changelog.md b/libraries/ghc-prim/changelog.md
index effa32479f..3df0b5e2ed 100644
--- a/libraries/ghc-prim/changelog.md
+++ b/libraries/ghc-prim/changelog.md
@@ -24,6 +24,10 @@
         interlockedExchangeAddr# :: Addr# -> Addr# -> State# s -> (# State# s, Addr# #)
         interlockedExchangeInt# :: Addr# -> Int# -> State# s -> (# State# s, Int# #)
 
+- Add an explicit fixity for `(~)` and `(~~)`: 
+
+        infix 4 ~, ~~
+
 ## 0.6.1 (edit as necessary)
 
 - Shipped with GHC 8.10.1