[Haskell-cafe] Optimization problem

[Lennart Augustsson]

On Sep 14, 2006, at 03:05 , Rohan Drape wrote:

>>> splitStreams [(3,x),(1,y),(3,z),(2,w)]
>> [(3,[x,z]),(1,[y]),(2,[w])]
>
> [snip]
>
>> Furthermore it should work on infinite lists. It can't eat the whole
>> list before producing any output.
>
> This doesn't seem to make sense?  Only at the end of the list can you
> know that you've collected all the events for each channel.  If you
> output anything before scanning to the end, you'd not know if there
> were perhaps more events on that channel?
It makes good sense.  Each list will of events will be evaluated  
lazily, so thing will appear there as they appear in the input.

I don't think you can do it in Haskell without some magic in the IO/ 
ST monad.

In LML we had an array construction function that did almost exactly  
what the O.P. asked for.

	-- Lennart