\begin{code}
-{-# OPTIONS -fno-implicit-prelude #-}
+{-# OPTIONS_GHC -fno-implicit-prelude #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Arr
%*********************************************************
\begin{code}
+-- | The 'Ix' class is used to map a contiguous subrange of values in
+-- a type onto integers. It is used primarily for array indexing
+-- (see "Data.Array", "Data.Array.IArray" and "Data.Array.MArray").
+--
+-- The first argument @(l,u)@ of each of these operations is a pair
+-- specifying the lower and upper bounds of a contiguous subrange of values.
+--
+-- An implementation is entitled to assume the following laws about these
+-- operations:
+--
+-- * @'inRange' (l,u) i == 'elem' i ('range' (l,u))@
+--
+-- * @'range' (l,u) '!!' 'index' (l,u) i == i@, when @'inRange' (l,u) i@
+--
+-- * @'map' ('index' (l,u)) ('range' (l,u))) == [0..'rangeSize' (l,u)-1]@
+--
+-- * @'rangeSize' (l,u) == 'length' ('range' (l,u))@
+--
+-- Minimal complete instance: 'range', 'index' and 'inRange'.
+--
class (Ord a) => Ix a where
+ -- | The list of values in the subrange defined by a bounding pair.
range :: (a,a) -> [a]
- index, unsafeIndex :: (a,a) -> a -> Int
+ -- | The position of a subscript in the subrange.
+ index :: (a,a) -> a -> Int
+ -- | Like 'index', but without checking that the value is in range.
+ unsafeIndex :: (a,a) -> a -> Int
+ -- | Returns 'True' the given subscript lies in the range defined
+ -- the bounding pair.
inRange :: (a,a) -> a -> Bool
+ -- | The size of the subrange defined by a bounding pair.
rangeSize :: (a,a) -> Int
+ -- | like 'rangeSize', but without checking that the upper bound is
+ -- in range.
+ --
+ -- As long as you don't override the default 'rangeSize', you can
+ -- specify 'unsafeRangeSize' as follows, to speed up some operations:
+ --
+ -- > unsafeRangeSize b@(_l,h) = unsafeIndex b h + 1
+ --
unsafeRangeSize :: (a,a) -> Int
-- Must specify one of index, unsafeIndex
| otherwise = error "Error in array index"
unsafeIndex b i = index b i
- -- As long as you don't override the default rangeSize,
- -- you can specify unsafeRangeSize as follows, to speed up
- -- some operations:
- --
- -- unsafeRangeSize b@(_l,h) = unsafeIndex b h + 1
- --
rangeSize b@(_l,h) | inRange b h = unsafeIndex b h + 1
| otherwise = 0
unsafeRangeSize b = rangeSize b