On 10/1/05, [EMAIL PROTECTED] <[EMAIL PROTECTED]> wrote: >
> > Hi there folks, I'm trying to learn some functional programming in Haskell, > well, at the College, but they don't teach anything, lol, so I have a very > simple question about type creation. > > This is a new type that contains the int and the new infinity number > > data NatInf = Infinity | Num Int > > At this point every seems to be ok, but when I load the file in Hugs, and > then write > > Num 5 (or Infinity) > > the following error appears: > > ERROR – Cannot find "show" function for: > *** Expression : Num 5 > *** Of type: : NatInf This means that you have not yet specified how you want your new data type to be converted to a string (using the function "show" in the Show type class). Either you write your own implementation instance Show NatInf where show (Num x) = ... show (Infinity) = ... Or you can simply derive a standard one by typing "deriving Show" at the end of your data declaration. data NatInf = Infinity | Num Int deriving Show /S -- Sebastian Sylvan +46(0)736-818655 UIN: 44640862
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