Re: [Haskell-cafe] Patterns for processing large but finite streams

Sure you can. runningAverage :: Int -> [Double] -> [Double] runningAverage n xs = let chunk = take n xs in (sum chunk / length chunk) : runningAverage (tail xs) Lazy lists are absolutely ideal for this purpose. Regards, Malcolm On 1 Jul 2011, at 07:33, Eugene Kirpichov wrote:

Plain old lazy lists do not allow me to combine multiple concurrent computations, e.g. I cannot define average from sum and length.

2011/7/1 Heinrich Apfelmus :

...

Eugene Kirpichov wrote:

...

I'm rewriting timeplot to avoid holding the whole input in memory, and naturally a problem arises:

How to represent large but finite streams and functions that process them, returning other streams or some kinds of aggregate values?

Examples: * Adjacent differences of a stream of numbers * Given a stream of numbers with times, split it into buckets by time of given width and produce a stream of (bucket, 50%,75% and 90% quantiles in this bucket) * Sum a stream of numbers

Is this, perhaps, what comonads are for? Or iteratees?

Plain old lazy lists?

Best regards, Heinrich Apfelmus

-- http://apfelmus.nfshost.com

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-- Eugene Kirpichov Principal Engineer, Mirantis Inc. http://www.mirantis.com/ Editor, http://fprog.ru/

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