-- |
-- 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
--
-- Class of index types.
--
+-- The "Ix" class is used to map a continuous subrange of values in a type onto
+-- integers. It is used primarily for array indexing (see Section 6
+-- <http://www.haskell.org/onlinelibrary/array.html#arrays>). The "Ix"
+-- class contains the methods range, index, and inRange. The 'index' operation
+-- maps a bounding pair, which defines the lower and upper bounds of the range,
+-- and a subscript, to an integer. The 'range' operation enumerates all
+-- subscripts; the 'inRange' operation tells whether a particular subscript
+-- lies in the range defined by a bounding pair.
+--
+-- An implementation is entitled to assume the following laws about these
+-- operations:
+--
+-- > range (l,u) !! index (l,u) i == i -- when i is in range
+--
+-- > inRange (l,u) i == i `elem` range (l,u)
+--
-----------------------------------------------------------------------------
-
module Data.Ix
(
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
#ifdef __GLASGOW_HASKELL__
import GHC.Arr
#endif
+
+#ifdef __HUGS__
+import Hugs.Prelude( Ix(..) )
+#endif
+
+#ifdef __NHC__
+import Ix (Ix(..))
+#endif
+