module Ix ( Ix(range, index, inRange), rangeSize ) where
import Prelude
class Ord a => Ix a where
range :: (a,a) -> [a]
index :: (a,a) -> a -> Int
inRange :: (a,a) -> a -> Bool
rangeSize :: Ix a => (a,a) -> Int
rangeSize b@(l,h) | null (range b) = 0
| otherwise = index b h + 1
-- NB: replacing "null (range b)" by "l > h" fails if
-- the bounds are tuples. For example,
-- (2,1) > (1,2),
-- but
-- range ((2,1),(1,2)) = []
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
{-
instance (Ix a, Ix b) => Ix (a,b) where
range ((l,l'),(u,u'))
= [(i,i') | i <- range (l,u), i' <- range (l',u')]
index ((l,l'),(u,u')) (i,i')
= index (l,u) i * rangeSize (l',u') + index (l',u') i'
inRange ((l,l'),(u,u')) (i,i')
= inRange (l,u) i && inRange (l',u') i'
-}