The documentation for the Show typeclass has this very example:
http://hackage.haskell.org/packages/archive/base/latest/doc/html/Prelude.html#t:Show
The summary? you need to define either showPrec or show, the latter of which is
simpler, it is just a -> String.
So:
instance Show (Tree Int Int) where
show (Tree (Node (k,v)) left right) = ...
On Jul 21, 2011, at 10:55 AM, Александр wrote:
> Hello, thank you for reply. I know that i can derive this. But i want to
> know how can i make it by hand.
>
> Thank you.
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