为什么putStrLn似乎可以改变IO monad中的预期类型?

我有以下基于csv管道的简单函数,它调用一个自定义 catMaybes 实施 Vector 美国。

retrieveSmaXtec :: IO (Vector SxRecord)
retrieveSmaXtec = do
  rows <- sourceFile "unordered.csv"
    .| intoCSV defCSVSettings
    .| sinkVector
    & runConduitRes
  putStrLn $ show $ size rows  -- DEBUG
  putStrLn $ show $ size $ (fmap fromRow rows) -- DEBUG
  rows & fmap fromRow & catMaybes & return

putStrLn fromRow 普斯特林 打电话,我得到错误:

src/FDS/Data/SmaXtec.hs:64:25: error:                                                                                                       
    * Couldn't match type `Map k0 (Maybe SxRecord)'                                                                                         
                     with `Vector (Maybe SxRecord)'                                                                                         
      Expected type: Map k0 (Maybe SxRecord) -> Vector SxRecord                                                                             
        Actual type: Vector (Maybe SxRecord) -> Vector SxRecord                                                                             
    * In the second argument of `(&)', namely `catMaybes'                                                                                   
      In the first argument of `(&)', namely                                                                                                
        `rows & fmap fromRow & catMaybes'                                                                                                   
      In a stmt of a 'do' block: rows & fmap fromRow & catMaybes & return                                                                   
    * Relevant bindings include                                                                                                             
        rows :: Map k0 (MapRow Text)                                                                                                        
          (bound at src/FDS/Data/SmaXtec.hs:58:3)                                                                                           
   |                                                                                                                                        
64 |   rows & fmap fromRow & catMaybes & return                                                                                             
   |                         ^^^^^^^^^           

更新: 正如评论中暗示的那样, size 不是我要找的功能。我需要 Data.Vector.length