Hi.
On 07/21/2011 04:45 PM, Александр wrote:
Hello,
I have binary tree, with every leaf tuple - (k,v):
data Tree k v = EmptyTree
| Node (k, v) (Tree k v) (Tree k v)
How can i make Show Instance for (Tree Int Int) ?
The easiest way is automatic derivation:
data Tree k v = EmptyTree
| Node (k, v) (Tree k v) (Tree k v)
deriving (Eq, Ord, Show, Read)
-- you normally want at least these four.
Then the compiler automatically declares the instances for you, given
that 'k' and 'v' have them. For k = v = Int, this is the case.
I try:
instance Show (Tree k v) where
show EmptyTree = show "Empty"
show (Node (Int, Int) left right) = ..
I'm afraid to say that, but 'Int' doesn't make sense at this place. You
would want
> show (Node (x, y) left right) = ...
instead. (That is, use any variables. Variables have to be lowercase.)
-- Steffen
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