[commit: base] master: Add isLeft/isRight (58d03b8)

[Ian Lynagh]

Repository : ssh://darcs.haskell.org//srv/darcs/packages/base

On branch  : master

https://github.com/ghc/packages-base/commit/58d03b8ed4342b80bd0ed8afa52c2b5c7f975534

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

commit 58d03b8ed4342b80bd0ed8afa52c2b5c7f975534
Author: Simon Hengel <sol at typeful.net>
Date:   Tue Dec 25 16:07:27 2012 +0100

    Add isLeft/isRight

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

 Data/Either.hs |   12 ++++++++++++
 1 files changed, 12 insertions(+), 0 deletions(-)

diff --git a/Data/Either.hs b/Data/Either.hs
index 0fd862e..166c4f2 100644
--- a/Data/Either.hs
+++ b/Data/Either.hs
@@ -23,6 +23,8 @@ module Data.Either (
    either,
    lefts,
    rights,
+   isLeft,
+   isRight,
    partitionEithers,
  ) where
 
@@ -97,6 +99,16 @@ partitionEithers = foldr (either left right) ([],[])
   left  a ~(l, r) = (a:l, r)
   right a ~(l, r) = (l, a:r)
 
+-- | Return `True` if the given value is a `Left`-value, `False` otherwise.
+isLeft :: Either a b -> Bool
+isLeft (Left  _) = True
+isLeft (Right _) = False
+
+-- | Return `True` if the given value is a `Right`-value, `False` otherwise.
+isRight :: Either a b -> Bool
+isRight (Left  _) = False
+isRight (Right _) = True
+
 {-
 {--------------------------------------------------------------------
   Testing