[Haskell-cafe] Types and hashes of hashes, trouble for a Java-programmer...

[John A. De Goes]

Why not use an ordered pair as the key?

Regards,

John A. De Goes
N-BRAIN, Inc.
The Evolution of Collaboration

http://www.n-brain.net    |    877-376-2724 x 101

On Apr 13, 2009, at 9:42 AM, John Smith wrote:

> Hi, a java-programmer running into trouble while trying to learn  
> Haskell.
>
> I try to make a hash containing hashes but can not getting a value  
> out of the innermost hash - I keep running into type-trouble where  
> IO and Maybe monad is getting mixed?
>
> My attempt:
>
>
> removeMaybeHash x =
>   case x of
>   Just ref -> ref
>   Nothing -> HashTable.new (==) (\key -> key)
>
>
> test = do
>   h <- HashTable.new (==) (\key -> key)
>   h1 <- HashTable.new (==) (\key -> key)
>   HashTable.insert h 3 h1
>   HashTable.insert h1 1 1000
>   maybeOuterHash <- HashTable.lookup h 3
>   res <- removeMaybe (removeMaybeHash maybeOuterHash) 1000
>   return res
>
> Any clues?
>
> In java this would be as simple as (pseudocode):  
> h.lookup(3).lookup(1000)
>
> Cheers,
>
> Pedro
>
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