Add MonadZip and MonadFix instances for Complex

These instances are taken from
https://hackage.haskell.org/package/linear-1.21/docs/Linear-Instances.html

They are the unique possible, so let they be in `base`.

2 files changed, 12 insertions, 0 deletions

diff --git a/libraries/base/Data/Complex.hs b/libraries/base/Data/Complex.hs
index a544a5bf6c..b32844057d 100644
--- a/libraries/base/Data/Complex.hs
+++ b/libraries/base/Data/Complex.hs
@@ -42,6 +42,8 @@ import GHC.Float (Floating(..))
 import Data.Data (Data)
 import Foreign (Storable, castPtr, peek, poke, pokeElemOff, peekElemOff, sizeOf,
                 alignment)
+import Control.Monad.Fix (MonadFix(..))
+import Control.Monad.Zip (MonadZip(..))
 
 infix  6  :+
 
@@ -251,6 +253,14 @@ instance Applicative Complex where
 instance Monad Complex where
   a :+ b >>= f = realPart (f a) :+ imagPart (f b)
 
+-- | @since 4.15.0.0
+instance MonadZip Complex where
+  mzipWith = liftA2
+
+-- | @since 4.15.0.0
+instance MonadFix Complex where
+  mfix f = (let a :+ _ = f a in a) :+ (let _ :+ a = f a in a)
+
 -- -----------------------------------------------------------------------------
 -- Rules on Complex
 
diff --git a/libraries/base/changelog.md b/libraries/base/changelog.md
index f612d29128..a0c3234137 100644
--- a/libraries/base/changelog.md
+++ b/libraries/base/changelog.md
@@ -25,6 +25,8 @@
 
   * An issue with list fusion and `elem` was fixed. `elem` applied to known
     small lists will now compile to a simple case statement more often.
+
+  * Add `MonadFix` and `MonadZip` instances for `Complex`
    
 ## 4.14.0.0 *TBA*
   * Bundled with GHC 8.10.1