[Haskell] why I need so much memory????

Ketil Malde ketil at ii.uib.no
Wed Nov 9 07:09:27 EST 2005

Alberto Fuentes Rodriguez wrote:

> isRepeated :: Eq a => [a] -> Bool
> isRepeated [] = False
> isRepeated (p:r) = (any (\x -> x == p) r) || isRepeated r
Two comments:
You can write "any (==p) r", using a partial application of the equality 
predicate.  Reads better IMHO.
This is O(n²), sorting and checking should be O(n log n).
You might be better off generating only unque hands from the start?  If 
you can generate a lazy stream of hands, and the stream can be consumed 
lazily, it will save a lot or memory. (Three comments, I mean)

> I call it with a [[Char]] of 2598960 elements and each element with 5 
> Characters.
> Ok the complexity is high but.... why this program needs 1GB (the 
> structure only has 20MB) of memory??
> The problem is that it begins to use the swap zone and due to that It 
> can only use the 10% of the processor.
You can try to limit the heap -- for me, about 80% of physical RAM seems 
to be a good choice.  (E.g. +RTS -M800M)


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