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" 5

insert 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 <bos@serpentine.com> wrote:

From: Bryan O'Sullivan <bos@serpentine.com>
Subject: Re: [Haskell-cafe] Hash table constructors return table in IO Monad. Why?
To: "Stephen Tetley" <stephen.tetley@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.tetley@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.

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