Question

我正在尝试在Haskell中学习Aeson库。现在，我正在尝试解析一个简单的JSON文件

{
    "Meta Data": {
        "1: Symbol": "MSFT",
        "2: Indicator": "Relative Strength Index (RSI)",
        "3: Last Refreshed": "2018-10-15",
        "4: Interval": "weekly",
        "5: Time Period": 10,
        "6: Series Type": "open",
        "7: Time Zone": "US/Eastern Time"
    },
    "Technical Analysis: RSI": {
        "2018-10-15": {
            "RSI": "54.5653"
        },
        "2018-10-12": {
            "RSI": "63.0279"
        },
        "2018-10-05": {
            "RSI": "74.7519"
        },
        "2018-09-28": {
            "RSI": "72.1573"
        },
        "2018-09-21": {
            "RSI": "74.8123"
        },
        "2018-09-14": {
            "RSI": "66.7116"
        },
        "2018-09-07": {
            "RSI": "75.8051"
        },
..and so on

在有关Aeson Aeson: the tutorial的本教程的帮助下特别是“嵌套记录”部分

这是我到目前为止所掌握的。

{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE OverloadedStrings #-}
{-# LANGUAGE RecordWildCards   #-}

module Tesst where

import           Data.Aeson
import qualified Data.ByteString.Lazy as B
import           Data.Time
import           GHC.Exts
import           GHC.Generics
import           Network.HTTP.Conduit (simpleHttp)

data TechinicalAnalysis = TechinicalAnalysis {
                   name :: String,
                   date :: String,
                   rsi  :: String
                   } deriving (Show, Generic)


instance FromJSON TechinicalAnalysis where
  parseJSON = withObject "RSI Quote" $
    \o -> do
      rsiQuote <- o        .: "Technical Analysis: RSI"
      date     <- rsiQuote .: "2018-10-16"
      rsi      <- date     .: "RSI"
      return TechinicalAnalysis {..}


main :: IO ()
main = do
  putStrLn "Which ticker? "
  symbolToQuote <- getLine
  d <- (eitherDecode <$> simpleHttp ("https://www.alphavantage.co/query?function=RSI&interval=weekly&time_period=10&series_type=open&apikey==FI2KMCSDSAE&symbol=" ++ symbolToQuote)) :: IO (Either String TechinicalAnalysis)
  case d of
    Left e   -> print e
    Right qt -> print (rsi qt)

我的目标是从链接的JSON文件中获取最新的“ RSI”报价。我现在不确定该怎么做，因此出于测试目的，我手动对"2018-10-16"部分中的密钥parseJSON进行了修改。

我运行代码的错误消息是

    • Couldn't match type ‘unordered-containers-0.2.9.0:Data.HashMap.Base.HashMap
                             Data.Text.Internal.Text Value’
                     with ‘[Char]’
      Expected type: String
        Actual type: Object
    • In the ‘date’ field of a record
      In the first argument of ‘return’, namely ‘TechinicalAnalysis {..}’
      In a stmt of a 'do' block: return TechinicalAnalysis {..}
   |
27 |       return TechinicalAnalysis {..}
   |              ^^^^^^^^^^^^^^^^^^^^^^^

我认为这是在告诉我，从date得到的响应date <- rsiQuote .: "2018-10-15"不是我所期望的。

Here，您可以找到我之前的问题以及后来发现的答案（不同的JSON文件，已成功解析）

Answer 1

我解决了这个问题。

.:返回的类型为Object而不是String

所以代替这个

data TechinicalAnalysis = TechinicalAnalysis {
                   name :: String,
                   date :: String,
                   rsi  :: String
                   } deriving (Show, Generic)

我为此感到愤怒

newtype TechinicalAnalysis = TechinicalAnalysis {
                   rsi  :: String
                   } deriving (Show, Generic)

，它无缝运行。

使用Aeson在Haskell中解析嵌套的JSON

1 个答案: