* Add Bifunctor instance suggested by Jonathan King

* Require base >= 4.8 for class Bifunctor

CHANGELOG.md

@@ -1,5 +1,13 @@
-0.4
+# 0.5
 
-* Generalize `Diff a` to `PolyDiff a b`.  `Diff` has been replaced with
-a specialized synonym `type Diff a = PolyDiff a a`, but it's still not
-backward compatible if you imported `Diff(..)`.
+	- Bring space complexity down to D^2 (Bodigrim)
+	- Add Bifunctor instance (Jonathan King.)  Requires base >= 4.8.
+	- Fix for the grouped context diff.  It was omitting all trailing
+	  context.
+	- Allow unlimited number of context elements (getContextDiffNew)
+
+# 0.4
+
+	- Generalize `Diff a` to `PolyDiff a b`.  `Diff` has been replaced with
+	  a specialized synonym `type Diff a = PolyDiff a a`, but it's still not
+	  backward compatible if you imported `Diff(..)`.

Diff.cabal

@@ -13,7 +13,7 @@ Cabal-Version:       >= 1.10
 
 library
   default-language: Haskell2010
-  build-depends:   base >= 3 && <= 6, array, pretty >= 1.1
+  build-depends:   base >= 4.8 && <= 6, array, pretty >= 1.1
   hs-source-dirs:  src
   exposed-modules:
                    Data.Algorithm.Diff,

src/Data/Algorithm/Diff.hs

@@ -26,8 +26,8 @@ module Data.Algorithm.Diff
     ) where
 
 import Prelude hiding (pi)
-
 import Data.Array (listArray, (!))
+import Data.Bifunctor
 
 data DI = F | S deriving (Show, Eq)
 
@@ -38,6 +38,11 @@ data DI = F | S deriving (Show, Eq)
 data PolyDiff a b = First a | Second b | Both a b
     deriving (Show, Eq)
 
+instance Bifunctor PolyDiff where
+  bimap f _ (First a) = First (f a)
+  bimap _ g (Second b) = Second (g b)
+  bimap f g (Both a b) = Both (f a) (g b)
+
 -- | This is 'PolyDiff' specialized so both sides are the same type.
 type Diff a = PolyDiff a a