Hi there, I have been busy for a couple of days now, to just get a bit more feeling on Haskell and I have read a bunch of tutorials, also about Monads and experimented of course. And now I want to use it for my real world problem. I think I understand the languageprinciples good enough, but I yet don't understand the syntax of all of the functioninterfaces. And that's my problem. I want to create the fastest array as possible in Haskell and I understood that I should use this function(the function below that creates a mutable array). The only problem is that I don't kwow how to use it. Constructing mutable arrays newArray :: (MArray a e m, Ix i) => (i, i) -> e -> m (a i e) Builds a new array, with every element initialised to undefined. Reading and writing mutable arrays readArray :: (MArray a e m, Ix i) => a i e -> i -> m e Read an element from a mutable array writeArray :: (MArray a e m, Ix i) => a i e -> i -> e -> m () Write an element in a mutable array I see it takes two arguments: a tuple of an index type(I use Int, so for example (0,1) 0 for the lower bound, 1 for the upper bound.) , but the e (according to "GHC documentation" it says the "element type"). Well the type of my elements should be my own datatype myDataType, but I can't even get it done to create simple mutable array's of Int or Bool. How can I make it work with my own datatype myDataType(could you give some examples for the use of the below functions?)? Is it OK to say that in Haskell any value that is put from an extern source of the program(reading a file, reading stdin etc.) to a really pure function, must be in a do notation(essentially being a Monadic operation)? So to put it more concrete: In any Haskell program that does IO there is always some function that has this form: do x<-someSource putBoundVariableToSomeOtherFunctionThatDoesMonadicOperations(restOfPureFunctionalProgramForExample x) So it's not possible to write some function that does the following: f::Int f do x<-getChar --suppose the Char is a number someSpecialReturnFunction x and than the result of the IO is only Int after some alterations of above code. P.S. Will it give any significant loss in speed if myDataType is lazy (no use of the !-sign in the constructors))? P.P.S. If there are array's that are even faster in Haskell, please let me know? Thanks in advance, Ron __________________________________ Do you Yahoo!? The New Yahoo! Search - Faster. Easier. Bingo. http://search.yahoo.com