base-4.0.0.0: Basic librariesContentsIndex
Data.Ix
Portabilityportable
Stabilitystable
Maintainerlibraries@haskell.org
Contents
The Ix class
Deriving Instances of Ix
Description
The Ix class is used to map a contiguous subrange of values in type onto integers. It is used primarily for array indexing (see the array package).
Synopsis
class Ord a => Ix a where
range :: (a, a) -> [a]
index :: (a, a) -> a -> Int
inRange :: (a, a) -> a -> Bool
rangeSize :: (a, a) -> Int
The Ix class
class Ord a => Ix a where

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 the array package).

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:

Minimal complete instance: range, index and inRange.

Methods
range :: (a, a) -> [a]
index :: (a, a) -> a -> Int
inRange :: (a, a) -> a -> Bool
rangeSize :: (a, a) -> Int
show/hide Instances
Ix Bool
Ix Char
Ix Int
Ix Int8
Ix Int16
Ix Int32
Ix Int64
Ix Integer
Ix Ordering
Ix Word
Ix Word8
Ix Word16
Ix Word32
Ix Word64
Ix ()
Ix IOMode
Ix GeneralCategory
Ix SeekMode
(Ix a, Ix b) => Ix ((,) a b)
(Ix a1, Ix a2, Ix a3) => Ix ((,,) a1 a2 a3)
(Ix a1, Ix a2, Ix a3, Ix a4) => Ix ((,,,) a1 a2 a3 a4)
(Ix a1, Ix a2, Ix a3, Ix a4, Ix a5) => Ix ((,,,,) a1 a2 a3 a4 a5)
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
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