2008/12/16 Magnus Therning
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 !!) where 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 memoization, like: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/data-memocombinat... http://hackage.haskell.org/cgi-bin/hackage-scripts/package/MemoTrie -- Felipe.