[commit: ghc] master: Simplify the defn of coreViewOneStarKind (21b4228)

[git at git.haskell.org]

Repository : ssh://git@git.haskell.org/ghc

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/21b4228d750198bdcac8d68d13892cc960d6881f/ghc

>---------------------------------------------------------------

commit 21b4228d750198bdcac8d68d13892cc960d6881f
Author: Simon Peyton Jones <simonpj at microsoft.com>
Date:   Wed Feb 17 14:36:49 2016 +0000

    Simplify the defn of coreViewOneStarKind
    
    I discussed it with Richard, but this version is much
    simmpler and more efficient.


>---------------------------------------------------------------

21b4228d750198bdcac8d68d13892cc960d6881f
 compiler/types/Type.hs | 11 +++++------
 1 file changed, 5 insertions(+), 6 deletions(-)

diff --git a/compiler/types/Type.hs b/compiler/types/Type.hs
index 1266b66..36da3a1 100644
--- a/compiler/types/Type.hs
+++ b/compiler/types/Type.hs
@@ -311,12 +311,11 @@ coreView _ = Nothing
 -- | Like 'coreView', but it also "expands" @Constraint@ to become
 -- @TYPE Lifted at .
 coreViewOneStarKind :: Type -> Maybe Type
-coreViewOneStarKind = go Nothing
-  where
-    go _ t | Just t' <- coreView t                    = go (Just t') t'
-    go _ (TyConApp tc []) | isStarKindSynonymTyCon tc = go (Just t') t'
-      where t' = liftedTypeKind
-    go res _ = res
+coreViewOneStarKind ty
+  | Just ty' <- coreView ty   = Just ty'
+  | TyConApp tc [] <- ty
+  , isStarKindSynonymTyCon tc = Just liftedTypeKind
+  | otherwise                 = Nothing
 
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 expandTypeSynonyms :: Type -> Type