X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FIx.hs;h=6af2c19e355bfc94fdb8d041a59c29a5655ddb8e;hb=c926c49d6a535729214d31815a748520561191a6;hp=f7d41f32cfb0cc068f9787b1d102014f3f06ef8a;hpb=9fa9bc17072a58c0bae2cce4764d38677e96ac29;p=ghc-base.git

diff --git a/Data/Ix.hs b/Data/Ix.hs
index f7d41f3..6af2c19 100644
--- a/Data/Ix.hs
+++ b/Data/Ix.hs
@@ -2,20 +2,20 @@
 -- |
 -- Module      :  Data.Ix
 -- Copyright   :  (c) The University of Glasgow 2001
--- License     :  BSD-style (see the file libraries/core/LICENSE)
+-- License     :  BSD-style (see the file libraries/base/LICENSE)
 -- 
 -- Maintainer  :  libraries@haskell.org
--- Stability   :  provisional
+-- Stability   :  stable
 -- Portability :  portable
 --
--- $Id: Ix.hs,v 1.3 2002/04/24 16:31:39 simonmar Exp $
---
--- Class of index types.
---
+-- The 'Ix' class is used to map a contiguous subrange of values in
+-- type onto integers.  It is used primarily for array indexing
+-- (see "Data.Array", "Data.Array.IArray" and "Data.Array.MArray").
+-- 
 -----------------------------------------------------------------------------
-
 module Data.Ix
     (
+    -- * The 'Ix' class
 	Ix
 	  ( range	-- :: (Ix a) => (a,a) -> [a]
 	  , index       -- :: (Ix a) => (a,a) -> a   -> Int
@@ -34,6 +34,30 @@ module Data.Ix
     --  ...
 
     -- Implementation checked wrt. Haskell 98 lib report, 1/99.
+
+    -- * Deriving Instances of 'Ix'
+    -- | Derived instance declarations for the class 'Ix' are only possible
+    -- for enumerations (i.e. datatypes having only nullary constructors)
+    -- and single-constructor datatypes, including arbitrarily large tuples,
+    -- whose constituent types are instances of 'Ix'. 
+    -- 
+    -- * For an enumeration, the nullary constructors are assumed to be
+    -- numbered left-to-right with the indices being 0 to n-1 inclusive. This
+    -- is the same numbering defined by the 'Enum' class. For example, given
+    -- the datatype: 
+    -- 
+    -- >	data Colour = Red | Orange | Yellow | Green | Blue | Indigo | Violet
+    -- 
+    -- we would have: 
+    -- 
+    -- >	range   (Yellow,Blue)        ==  [Yellow,Green,Blue]
+    -- >	index   (Yellow,Blue) Green  ==  1
+    -- >	inRange (Yellow,Blue) Red    ==  False
+    -- 
+    -- * For single-constructor datatypes, the derived instance declarations
+    -- are as shown for tuples in Figure 1
+    -- <http://www.haskell.org/onlinelibrary/ix.html#prelude-index>.
+
     ) where
 
 import Prelude
@@ -41,3 +65,12 @@ import Prelude
 #ifdef __GLASGOW_HASKELL__
 import GHC.Arr
 #endif
+
+#ifdef __HUGS__
+import Hugs.Prelude( Ix(..) )
+#endif
+
+#ifdef __NHC__
+import Ix (Ix(..))
+#endif
+