I am still stuck with the problem of creating an IOArray. I have tried the following: import Data.Ix import Data.Array.MArray import Monad import IO import Data.Array.IO test=newArray (0,1) IOArray But this doesn't work because the dataconstructor is not in scope, although I have imported all imaginable modules. Then I tried: test=newArray (0,1) Lesson GHC told me I needed to create an instance of MArray with it's type, but I had no idea of how to do such thing. So I went experimenting with type classes when I encountered something very strange. data Lesson=Lesson String Int Int String String instance Show Lesson where show (Lesson s1 i1 i2 s2 s3) = show s1 Why does above instance of Show works with Hugs, but not with GHC 5.04.2 (see error below)? {- Compiling Test ( test.hs, interpreted ) test.hs:38: Ambiguous occurrence `show' It could refer to either `Test.show', defined at test.hs:38 or `GHC.Show.show', imported from Prelude at test.hs:1 Failed, modules loaded: none. I now have two pieces of information, at least I think so: I need some instance of my an MArray of my datatype Lesson as an elementtype. And I need some way of integrating the IOArray in that definition. Although this statement is completely easy for an experimented Haskellprogrammer, but it isn't for me. Can somebody please help me with some concrete stuff (I do understand it's better to do it yourself, but I really don't know how to get any further)? Greets Ron __________________________________ Do you Yahoo!? The New Yahoo! Search - Faster. Easier. Bingo. http://search.yahoo.com