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module Ix ( Ix(range, index, inRange, rangeSize) ) where
class Ord a => Ix a where
range :: (a,a) -> [a]
index :: (a,a) -> a -> Int
inRange :: (a,a) -> a -> Bool
rangeSize :: (a,a) -> Int
rangeSize b@(l,h) | null (range b) = 0
| otherwise = index b h + 1
-- NB: replacing "null (range b)" by "not (l <= h)"
-- fails if the bounds are tuples. For example,
-- (1,2) <= (2,1)
-- but the range is nevertheless empty
-- range ((1,2),(2,1)) = []
instance Ix Char where
range (m,n) = [m..n]
index b@(c,c') ci
| inRange b ci = fromEnum ci - fromEnum c
| otherwise = error "Ix.index: Index out of range."
inRange (c,c') i = c <= i && i <= c'
instance Ix Int where
range (m,n) = [m..n]
index b@(m,n) i
| inRange b i = i - m
| otherwise = error "Ix.index: Index out of range."
inRange (m,n) i = m <= i && i <= n
instance Ix Integer where
range (m,n) = [m..n]
index b@(m,n) i
| inRange b i = fromInteger (i - m)
| otherwise = error "Ix.index: Index out of range."
inRange (m,n) i = m <= i && i <= n
instance (Ix a,Ix b) => Ix (a, b) -- as derived, for all tuples
instance Ix Bool -- as derived
instance Ix Ordering -- as derived
instance Ix () -- as derived
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