Am 31.03.2011 05:59, schrieb Felipe Almeida Lessa:
On Wed, Mar 30, 2011 at 2:39 PM, Gilberto Garcia<giba....@gmail.com> wrote:
fkSum :: Int -> [Int] -> Int
fkSum a [] = 0
fkSum a (b) = foldl (+) 0 (filter (\x -> isMultiple x b) [1..a])
Daniel Fischer and Yves Parès gave you good suggestions about
implementing a different, better algorithm for you problem. However,
there's one small thing about your current code. Instead of foldl,
you should use foldl' (use "import Data.List"), which is strict in the
accumulator. Most of the time you want foldl' instead of foldl. You
can learn more about the list folds here [1].
Since we don't have a function sum' in the Prelude (should we have it?)
I wonder what happens if you just use "sum". Will the "sum" (based on
sum' so without -DUSE_REPORT_PRELUDE) be strict enough?
#ifdef USE_REPORT_PRELUDE
sum = foldl (+) 0
product = foldl (*) 1
#else
sum l = sum' l 0
where
sum' [] a = a
sum' (x:xs) a = sum' xs (a+x)
product l = prod l 1
where
prod [] a = a
prod (x:xs) a = prod xs (a*x)
#endif
Cheers C.
P.S.
isMultiple a = any ((== 0) . mod a)
HTH,
[1] http://www.haskell.org/haskellwiki/Foldr_Foldl_Foldl%27
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