使用CSV管道将CSV文件解析为自定义数据类型

我对如何将csv管道与自定义数据类型一起使用感到非常困惑。我想获取一行股票数据，例如：

Date,Open,High,Low,Close,Volume,Adj Close
2017-02-10,2312.27002,2319.22998,2311.100098,2316.100098,3475020000,2316.100098

并将其解析为我在下面的MWE中声明的StockInfo类型。我从文档中收集了使我的StockInfo成为FromNamedRecord、ToNamedRecord和CSV ByteString实例所需的信息。我相信我已经在前两个版本中这样做了，但是我不知道如何通过TestRing实现CSV所需的方法。任何帮助都将不胜感激

MWE：

---

以下是我应该做的：

{-# LANGUAGE OverloadedStrings     #-}

module Lib
    ( readStocks
    ) where

import           Data.ByteString
import           Data.Conduit
import           Data.Conduit.Binary
import           Data.CSV.Conduit
import           Data.CSV.Conduit.Conversion
import           Data.Text                   (Text)
import           Data.Vector
import           System.IO

readStocks :: FilePath -> IO (Vector (Named StockInfo))
readStocks fp = readCSVFile defCSVSettings fp

data StockInfo = StockInfo
  { date     :: !String
  , open     :: !Double
  , high     :: !Double
  , low      :: !Double
  , close    :: !Double
  , volume   :: !Integer
  , adjClose :: !Double
  } deriving (Show, Eq, Read)

instance FromNamedRecord StockInfo where
  parseNamedRecord m =
    StockInfo <$>
    m .: "Date" <*>
    m .: "Open" <*>
    m .: "High" <*>
    m .: "Low" <*>
    m .: "Close" <*>
    m .: "Volume" <*>
    m .: "Adj Close"

instance ToNamedRecord StockInfo where
  toNamedRecord (StockInfo date open high low close volume adjClose) =
    namedRecord [ "Date" .= date
                , "Open" .= open
                , "High" .= high
                , "Low" .= low
                , "Close" .= close
                , "Volume" .= volume
                , "Adj Close" .= adjClose
                ]

---

以下是我应该做的：

{-# LANGUAGE OverloadedStrings     #-}

module Lib
    ( readStocks
    ) where

import           Data.ByteString
import           Data.Conduit
import           Data.Conduit.Binary
import           Data.CSV.Conduit
import           Data.CSV.Conduit.Conversion
import           Data.Text                   (Text)
import           Data.Vector
import           System.IO

readStocks :: FilePath -> IO (Vector (Named StockInfo))
readStocks fp = readCSVFile defCSVSettings fp

data StockInfo = StockInfo
  { date     :: !String
  , open     :: !Double
  , high     :: !Double
  , low      :: !Double
  , close    :: !Double
  , volume   :: !Integer
  , adjClose :: !Double
  } deriving (Show, Eq, Read)

instance FromNamedRecord StockInfo where
  parseNamedRecord m =
    StockInfo <$>
    m .: "Date" <*>
    m .: "Open" <*>
    m .: "High" <*>
    m .: "Low" <*>
    m .: "Close" <*>
    m .: "Volume" <*>
    m .: "Adj Close"

instance ToNamedRecord StockInfo where
  toNamedRecord (StockInfo date open high low close volume adjClose) =
    namedRecord [ "Date" .= date
                , "Open" .= open
                , "High" .= high
                , "Low" .= low
                , "Close" .= close
                , "Volume" .= volume
                , "Adj Close" .= adjClose
                ]

---

库已经定义了一个实例，从NamedRecord a到NamedRecord a，CSV s MapRow ByteString=>CSV s Named a-Named只是标识，并且您有{To/From}NamedRecord实例，所以您不需要自己编写这个实例-只需使用命名实例即可。如果你真的愿意，你可以根据库提供的通用实例，通过TestRing StockInfo实例来定义你的CSV。明白了！我认为这没有什么意义，但这是我对它的最好理解。库已经定义了一个实例，从NamedRecord a到NamedRecord a，CSV s MapRow ByteString=>CSV s Named a-Named只是标识，您有{To/From}NamedRecord实例，因此，您不需要自己编写这个实例，只需使用命名实例即可。如果你真的愿意，你可以根据库提供的通用实例，通过TestRing StockInfo实例来定义你的CSV。明白了！我认为这没有道理，但这是我最好的理解。