Didier, See below... legajid wrote:

Hi, My purpose is to get data from the keyboard and return a maybe value, saying "nothing" if the data entered is invalid. I get a message "could'nt match expected IO Integer against inferred type maybe integer" on line x<- getdata Why should x be Maybe ? getdatanum is, but getdata is not.

Is it possible to write only one function rather than 2 distinct ones ?

Thanks for your help, Didier.

Here's my code

getdata :: IO Integer getdata=do x<-getLine let xn=read x ::Integer return xn

getdatanum :: Maybe Integer getdatanum = do x <- getdata {- if x < 5 then do return (Just x) else do return Nothing -} return (Just x)

The type of getdatanum should be IO (Maybe Integer). Maybe and IO are both monads, and that's why the error messages can be a bit confusing sometimes. Yes, you certainly can write this as one function. Steve