iarray-coerce.hs

import Data.Array
import Data.Array.IArray (IArray)
import Data.Array.Unboxed (UArray)
import Data.Array.ST (STArray, thaw, freeze)
import Control.Monad.ST (ST, runST)

coerce :: (Ix i, IArray a e, IArray b e) => a i e -> b i e
coerce arr = runST $ thawST arr >>= freeze
  where
    thawST :: (Ix i, IArray a e) => a i e -> ST s (STArray s i e)
    thawST = thaw

main = print $ (coerce $ listArray (0,3) [0..3] :: UArray Int Int)