[Haskell-cafe] How to think about this? (profiling)
felipe.lessa at gmail.com
Tue Dec 16 07:19:33 EST 2008
2008/12/16 Magnus Therning <magnus at therning.org>:
> That is, where each value depends on _all_ preceding values. AFAIK
> list access is linear, is there a type that is a more suitable state
> for this changed problem?
> I realise this particular function can be written using scanl:
> but I guess it's not always that easy to construct a solution based on scanl.
You can always write something like
> foo :: Int -> Int
> foo = (vals !!)
> vals = map foo' [0..]
> foo' 0 = 0
> foo' 1 = 1
> foo' 2 = 2
> foo' n = sum $ map foo [0..n-1]
which doesn't prevent you from using whatever recursive case you want.
Note that if your recursive case depends on all preceding values, then
you can't do better than using a linear access data structure like a
list unless you need random access.
I should point out as well that there are some packages on Hackage for
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