On Sep 10, 2004, at 3:37 PM, Stephan Zaubzer wrote:
Hello Everyone!
I am relatively new to Haskell (actually it's my second day) and I have the following problem: If I define a new datatype, for example a Binary tree, how can i use the show function to put an instance of my datatype into a String representation. I have seen in different Tutorials that there is a way for overloading the show function for my own type, and I tried out, what was presented in the tutorials, but it didn't work. Does somebody know, how to manage this?
Here my attempts:
data Entry a = EmptyEntry | MakeEntry a a
You could make use of the default show by simply deriving Show: data Entry a = EmptyEntry | MakeEntry a a deriving Show Otherwise you need to provide an instance of Show for your type, as such: instance Show a => Show (Entry a) where show EmptyEntry = "Empty" show (MakeEntry x y) = show x ++ ": " ++ show y (untested code) -marius