[commit: ghc] master: Remove redundant contexts from Foldable methods (0a8e899)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/0a8e8995fd31dd46fa9bdbc7f65984b51c8c13dc/ghc

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

commit 0a8e8995fd31dd46fa9bdbc7f65984b51c8c13dc
Author: David Feuer <David.Feuer at gmail.com>
Date:   Wed Nov 5 08:42:59 2014 +0100

    Remove redundant contexts from Foldable methods
    
    New `Foldable` methods accidentally had `Foldable` contexts, which led
    to type roles being assigned incorrectly and preventing GND from
    deriving `Foldable` instances. Removing those fixes #9761.
    
    Moreover, this patch takes advantage of this fix by deriving
    `Foldable` (and `Eq`) for `UniqFM`.
    
    Differential Revision: https://phabricator.haskell.org/D425


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

0a8e8995fd31dd46fa9bdbc7f65984b51c8c13dc
 compiler/utils/UniqFM.lhs                   | 20 +++-----------------
 libraries/base/Data/Foldable.hs             | 14 +++++++-------
 testsuite/tests/ghci/scripts/ghci025.stdout |  3 +--
 3 files changed, 11 insertions(+), 26 deletions(-)

diff --git a/compiler/utils/UniqFM.lhs b/compiler/utils/UniqFM.lhs
index 3ea97e4..f0f9035 100644
--- a/compiler/utils/UniqFM.lhs
+++ b/compiler/utils/UniqFM.lhs
@@ -72,7 +72,6 @@ import Outputable
 
 import Compiler.Hoopl   hiding (Unique)
 
-import Data.Function (on)
 import qualified Data.IntMap as M
 import qualified Data.IntSet as S
 import qualified Data.Foldable as Foldable
@@ -212,22 +211,9 @@ instance Monoid (UniqFM a) where
 %************************************************************************
 
 \begin{code}
-newtype UniqFM ele = UFM { unUFM :: M.IntMap ele }
-  deriving (Typeable,Data, Traversable.Traversable, Functor)
-
-instance Eq ele => Eq (UniqFM ele) where
-    (==) = (==) `on` unUFM
-
-{-
-instance Functor UniqFM where
-   fmap f = fmap f . unUFM
-
-instance Traversable.Traversable UniqFM where
-    traverse f = Traversable.traverse f . unUFM
--}
-
-instance Foldable.Foldable UniqFM where
-    foldMap f = Foldable.foldMap f . unUFM
+newtype UniqFM ele = UFM (M.IntMap ele)
+  deriving (Data, Eq, Foldable.Foldable, Functor, Traversable.Traversable,
+            Typeable)
 
 emptyUFM = UFM M.empty
 isNullUFM (UFM m) = M.null m
diff --git a/libraries/base/Data/Foldable.hs b/libraries/base/Data/Foldable.hs
index 9d26f86..4167b92 100644
--- a/libraries/base/Data/Foldable.hs
+++ b/libraries/base/Data/Foldable.hs
@@ -145,28 +145,28 @@ class Foldable t where
                          Just x  -> f x y)
 
     -- | List of elements of a structure.
-    toList :: Foldable t => t a -> [a]
+    toList :: t a -> [a]
     {-# INLINE toList #-}
     toList t = build (\ c n -> foldr c n t)
 
     -- | Test whether the structure is empty.
-    null :: Foldable t => t a -> Bool
+    null :: t a -> Bool
     null = foldr (\_ _ -> False) True
 
     -- | Returns the size/length of a finite structure as an 'Int'.
-    length :: Foldable t => t a -> Int
+    length :: t a -> Int
     length = foldl' (\c _ -> c+1) 0
 
     -- | Does the element occur in the structure?
-    elem :: (Foldable t, Eq a) => a -> t a -> Bool
+    elem :: Eq a => a -> t a -> Bool
     elem = any . (==)
 
     -- | The largest element of a non-empty structure.
-    maximum :: (Foldable t, Ord a) => t a -> a
+    maximum :: Ord a => t a -> a
     maximum = foldr1 max
 
     -- | The least element of a non-empty structure.
-    minimum :: (Foldable t, Ord a) => t a -> a
+    minimum :: Ord a => t a -> a
     minimum = foldr1 min
 
     -- | The 'sum' function computes the sum of the numbers of a structure.
@@ -175,7 +175,7 @@ class Foldable t where
 
     -- | The 'product' function computes the product of the numbers of a
     -- structure.
-    product :: (Foldable t, Num a) => t a -> a
+    product :: Num a => t a -> a
     product = getProduct . foldMap Product
 
 -- instances for Prelude types
diff --git a/testsuite/tests/ghci/scripts/ghci025.stdout b/testsuite/tests/ghci/scripts/ghci025.stdout
index 4d21c5f..e5654b3 100644
--- a/testsuite/tests/ghci/scripts/ghci025.stdout
+++ b/testsuite/tests/ghci/scripts/ghci025.stdout
@@ -53,8 +53,7 @@ class Eq a where
   (GHC.Classes./=) :: a -> a -> GHC.Types.Bool
 -- imported via Prelude, T
 Prelude.length ::
-  Data.Foldable.Foldable t =>
-  forall a. Data.Foldable.Foldable t => t a -> GHC.Types.Int
+  Data.Foldable.Foldable t => forall a. t a -> GHC.Types.Int
 -- imported via T
 data T.Integer
   = integer-gmp-0.5.1.0:GHC.Integer.Type.S# GHC.Prim.Int#