I was trying to convert some code from ordinary boxed array to unboxed arrays for performance reasons. Presumably the conversion, according to the GHC documentation should only involve appropriate type signatures (e.g. using UArray instead of Array) and importing Data.Array.Unboxed. However my code ultimately failed because I load a large array saved as a text file using the derived Read, Show mechanism. For some reason there is no Read function for unboxed arrays. Here is a little GHCI session showing the problem: Prelude> :m Data.Array.Unboxed Prelude Data.Array.Unboxed> let e = listArray (0,3) [0 .. 3] :: UArray Int Int Prelude Data.Array.Unboxed> let se = show e Prelude Data.Array.Unboxed> se "array (0,3) [(0,0),(1,1),(2,2),(3,3)]" Prelude Data.Array.Unboxed> let e2 = read se :: UArray Int Int <interactive>:1:9: No instance for (Read (UArray Int Int)) arising from use of `read' at <interactive>:1:9-15 Possible fix: add an instance declaration for (Read (UArray Int Int)) In the expression: read se In the expression: read se :: UArray Int Int In the definition of `e2': e2 = read se :: UArray Int Int However if I try to read it in as boxed arrays, no problem: Prelude Data.Array.Unboxed> let e2 = read se :: Array Int Int Prelude Data.Array.Unboxed> e2 array (0,3) [(0,0),(1,1),(2,2),(3,3)] Is there a reason why this doesn't work? Is it a design choice or does it merely reflect the fact that no one has gotten around to writing a read function for unboxed arrays. I imagine it would be trivial to fix this however.