X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=GHC%2FArr.lhs;h=b376c2fc1db0aaf415e3e62edd39e6127f75ba54;hb=7e8c7becf29c0fd359ff7e205b60df3ef4b920fb;hp=ede18bcea7701822c99df69bb22846e375adde69;hpb=70d7c4b1cdc78fe03f63180c318d2ca15f4f6a26;p=ghc-base.git diff --git a/GHC/Arr.lhs b/GHC/Arr.lhs index ede18bc..b376c2f 100644 --- a/GHC/Arr.lhs +++ b/GHC/Arr.lhs @@ -37,11 +37,46 @@ default () %********************************************************* \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 @@ -49,12 +84,6 @@ class (Ord a) => Ix a where | 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