Hmm, this is very helpful - didn't know it existed. Thanks very much, I'll
check it out!
Tim
On Thu, Jun 23, 2016 at 7:41 AM, David McBride
The problem isn't with array, but rather your index. Ix instances are always sorted in ascending order, as you might imagine. You can however, use your own index in arrays and they can be indexed in whatever order you like.
{-# LANGUAGE GeneralizedNewtypeDeriving #-}
import Data.Array import Data.Ix
newtype MyIx = MyIx Int deriving (Eq, Num, Show)
instance Ord MyIx where compare (MyIx a) (MyIx b) = case compare a b of LT -> GT GT -> LT EQ -> EQ
instance Ix MyIx where range (MyIx a, MyIx b) = map MyIx $ reverse [b..a] index (MyIx a, MyIx b) (MyIx c) = a - c inRange (MyIx a, MyIx b) (MyIx c) = c <= a && c >= b
blah :: Array MyIx Char blah = array (3,0) [(0,'a'),(1,'b'),(2,'c'),(3,'d')]
Warning: I only very lightly tested the above code.
You can mix your index and normal indexes to get the row / col ordering you are hoping for.
blah2 :: [((MyIx, Int), Char)] -> Array (MyIx, Int) Char blah2 = array ((3,0),(0,3))
Finally, if you are really looking for something that is designed to be a matrix, you might try one of several libraries that are out there, like hmatrix.
Hopefully this helps.