fp Sat Aug 4 15:21:38 +08 2018

constructs.hs

import Data.List
import Data.List.Split
-- a :: Num a => [a]
a = [1..10]
-------------------------------------------------------------------------------
myreverse xxs =
    case xxs of
    [] -> []
    (x:xs) -> myreverse xs ++ [x]
-------------------------------------------------------------------------------
mean0 xxs = sum xxs / fromIntegral (length xxs)
-------------------------------------------------------------------------------
mean1 xxs = sum xxs / genericLength xxs
-------------------------------------------------------------------------------
mean2 xxs = s/n
    where
    s = sum xxs
    n = fromIntegral(length xxs)
    --n = length xxs
-------------------------------------------------------------------------------
avg = go 0 0
    where 
    go a n [] = a/n
    go a n (x : xs) = go (a + x) (n + 1) xs
-------------------------------------------------------------------------------
f0 :: [a] -> [a]
f0 = (reverse =<<) . chunksOf 2 
-------------------------------------------------------------------------------
chunks :: Int -> [a] -> [[a]]
chunks _ [] = []
chunks n xs =
    let (ys, zs) = splitAt n xs
    in  ys : chunks n zs
-------------------------------------------------------------------------------
chunks0 n = takeWhile (not.null) . unfoldr (Just . splitAt n)