haskell - 过滤列表中的位置，Haskell

Question

我需要打印奇数索引的元素。目前是打印索引。

我不明白如何打印此索引的元素？

f :: [Int] -> [Int]
f lst = filter odd [0..length lst]

-- I can't edit this part
main = do
   inputdata <- getContents
   mapM_ (putStrLn. show). f. map read. lines $ inputdata

Answer 1

如果您想“步行”执行此操作:

odds [] = []
odds [x] = []
odds (e1:e2:xs) = e2 : odds xs