[Haskell-cafe] Re: [Haskell] Re: Global Variables and IO initializers

Jules Bean jules at jellybean.co.uk
Mon Nov 8 07:29:38 EST 2004

On 8 Nov 2004, at 12:23, Lennart Augustsson wrote:

> Adrian Hey wrote:
>> 4- They already exist (stdin,stout,stderr) and I don't
>>    recall anybody ever complaining about this.
> stdin, stdout, and stderr are not global variables.
> They are just handles.  One possible implementation
> of handles is as an Int.  So stdin is no more a global
> variable than 0.  Of course you need some state
> associated with the handle, but that state does not
> have to be a unique global things.  You are passing
> that state around via the IO monad, and there could
> be multiple versions of it.  GHC chooses to implement
> it differently, but that's a choice.

Yes... a lot of the example we have seen here are 'just' handles. 
newIORef creates handles.  Something many programmers would like is the 
ability to create fresh handles at the toplevel...


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