[Haskell-cafe] Hash table constructors return table in IO Monad. Why?
Is there some reason why ALL the ways to create a hash table return one in the IO Monad, but all the functions for retrieving a value from a hash table take as an argument a hash table NOT in the IO Monad? Michael = Prelude Data.HashTable let ht = fromList id [(5,'a'),(6,'b')]Prelude Data.HashTable fmap ((flip Data.HashTable.lookup) 6) htPrelude Data.HashTable Prelude Data.HashTable :t fmap ((flip Data.HashTable.lookup) 6) htfmap ((flip Data.HashTable.lookup) 6) ht :: IO (IO (Maybe Char)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why?
The hashtable needs to be been created in IO, after that, think of the 'hashtable' as a analogous to a file handle. You have to pass it around to do anything with it - but the only things you can do with it are in IO. (That's why no-one really likes it, of course...) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why?
On Thu, May 12, 2011 at 9:22 AM, Stephen Tetley stephen.tet...@gmail.comwrote: The hashtable needs to be been created in IO, after that, think of the 'hashtable' as a analogous to a file handle. You have to pass it around to do anything with it - but the only things you can do with it are in IO. The appropriate pure package to be using instead is unordered-containers. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why?
Thanks, Bryan and Stephan. I seem to remember playing around with a data structure that accumulates (in a list) different values associated with an identical key, i.e., insert data-structure abc 5insert data-structure abc 6 retrieve data-structure abc - [5,6] HashTable doesn't do it. Neither does Map. Was I dreaming? Michael --- On Thu, 5/12/11, Bryan O'Sullivan b...@serpentine.com wrote: From: Bryan O'Sullivan b...@serpentine.com Subject: Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why? To: Stephen Tetley stephen.tet...@gmail.com Cc: haskell-cafe@haskell.org Date: Thursday, May 12, 2011, 2:22 PM On Thu, May 12, 2011 at 9:22 AM, Stephen Tetley stephen.tet...@gmail.com wrote: The hashtable needs to be been created in IO, after that, think of the 'hashtable' as a analogous to a file handle. You have to pass it around to do anything with it - but the only things you can do with it are in IO. The appropriate pure package to be using instead is unordered-containers. -Inline Attachment Follows- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why?
On 12 May 2011 20:59, michael rice nowg...@yahoo.com wrote: HashTable doesn't do it. Neither does Map. Was I dreaming? I suppose you could implement this functionality on top of either. HTH, Ozgur ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why?
On Thu, May 12, 2011 at 12:59 PM, michael rice nowg...@yahoo.com wrote: HashTable doesn't do it. Neither does Map. Was I dreaming? multiInsert k v m = insertWith' (++) k [v] m ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why?
I guess everyone has weighed in. I must have been hallucinating. Yes, this will work. Thanks, Michael --- On Thu, 5/12/11, Bryan O'Sullivan b...@serpentine.com wrote: From: Bryan O'Sullivan b...@serpentine.com Subject: Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why? To: michael rice nowg...@yahoo.com Cc: Stephen Tetley stephen.tet...@gmail.com, haskell-cafe@haskell.org Date: Thursday, May 12, 2011, 6:04 PM On Thu, May 12, 2011 at 12:59 PM, michael rice nowg...@yahoo.com wrote: HashTable doesn't do it. Neither does Map. Was I dreaming? multiInsert k v m = insertWith' (++) k [v] m ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
