[commit: packages/base] master: Add `instance {Bits, FiniteBits} Bool` (d679f5e)

[git at git.haskell.org]

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

On branch  : master
Link       : http://ghc.haskell.org/trac/ghc/changeset/d679f5e9b57935fb0c04ddccb85c69881212979a/base

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

commit d679f5e9b57935fb0c04ddccb85c69881212979a
Author: Herbert Valerio Riedel <hvr at gnu.org>
Date:   Sun Nov 24 13:14:16 2013 +0100

    Add `instance {Bits,FiniteBits} Bool`
    
    This interprets `Bool` as an 1-bit "unsigned" bit-field and provides a
    simple (not particularily optimized) implementation to that end.
    
    See "Proposal: Add `instance Bits Bool`" by @ekmett, Nov 2013,
    
     http://permalink.gmane.org/gmane.comp.lang.haskell.libraries/20663
    
    Signed-off-by: Herbert Valerio Riedel <hvr at gnu.org>


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

d679f5e9b57935fb0c04ddccb85c69881212979a
 Data/Bits.hs |   35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)

diff --git a/Data/Bits.hs b/Data/Bits.hs
index 2654a80..f43c8a5 100644
--- a/Data/Bits.hs
+++ b/Data/Bits.hs
@@ -303,6 +303,41 @@ popCountDefault = go 0
    go c w = go (c+1) (w .&. (w - 1)) -- clear the least significant
 {-# INLINABLE popCountDefault #-}
 
+
+-- Interpret 'Bool' as 1-bit bit-field; /Since: 4.7.0.0/
+instance Bits Bool where
+    (.&.) = (&&)
+
+    (.|.) = (||)
+
+    xor = (/=)
+
+    complement = not
+
+    shift x 0 = x
+    shift _ _ = False
+
+    rotate x _ = x
+
+    bit 0 = True
+    bit _ = False
+
+    testBit x 0 = x
+    testBit _ _ = False
+
+    bitSizeMaybe _ = Just 1
+
+    bitSize _ = 1
+
+    isSigned _ = False
+
+    popCount False = 0
+    popCount True  = 1
+
+instance FiniteBits Bool where
+    finiteBitSize _ = 1
+
+
 instance Bits Int where
     {-# INLINE shift #-}
     {-# INLINE bit #-}