Look in Data.Int for a list of the Int types.

Basically you generally only use Int unless you are working at a lower-level which has an explicit requirement for the number of bits.  In this case, HashTable has such a requirement, so you have two choices:  you can either change the type annotation on dummy:


import Data.Int

dummy:: String -> Int32
dummy s = 7



or you can just leave it off entirely, and GHC will automatically infer the correct type (without you needing to import Data.Int):

dummy s = 7


On Nov 17, 2009, at 12:09 PM, michael rice wrote:

Hi Daniel,

Thanks for the IO monad reminder.

What is GHC.Int.Int32? Can't find it on Hoogle.

Michael

==================

*Main> ht <- new (==) dummy :: IO MyHashTable

<interactive>:1:15:
    Couldn't match expected type `GHC.Int.Int32'
           against inferred type `Int'
    In the second argument of `new', namely `dummy'
    In a stmt of a 'do' expression:
        ht <- new (==) dummy :: IO MyHashTable
*Main> :t dummy
dummy :: String -> Int
*Main>



--- On Tue, 11/17/09, Daniel Fischer <daniel.is.fischer@web.de> wrote:

From: Daniel Fischer <daniel.is.fischer@web.de>
Subject: Re: [Haskell-cafe] Simple hash table creation
To: haskell-cafe@haskell.org
Date: Tuesday, November 17, 2009, 2:45 PM

Am Dienstag 17 November 2009 20:36:46 schrieb Daniel Fischer:
> What you probably wanted was
>
> type MyHashTable = HashTable String Int -- not data MyHashTable
>

Just in case it's not clear:

> ht <- new (==) dummy :: IO MyHashTable

only works at the prompt or in an IO do-block, not at the top level of the module.

>
> then ht is a hashtable of type MyHashTable.


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