Prelude.read：没有解析&&无法将预期类型"Double"与实际类型"Text"匹配 在"天气值"的第一个参数中，即"tempMin"

Question

我该如何修复它？Couldn't match expected type ‘Double’ with actual type ‘Text’我不能用文本代替替身。这是一个回应

响应

{responseStatus = Status {statusCode = 200, statusMessage = "OK"}, 
responseVersion = HTTP/1.1, responseHeaders = [("Server","openresty"),
("Date","Wed, 16 May 2018 11:12:26 GMT"),("Content-Type","application/json; 
charset=utf-8"),("Content-Length","446"),("Connection","keep-alive"),("X-Cache-
Key","/data/2.5/weather?q=yerevan,am"),("Access-Control-Allow-Origin","*"),
("Access-Control-Allow-Credentials","true"),("Access-Control-Allow-
Methods","GET, POST")], responseBody = "{"coord":
{"lon":44.51,"lat":40.18},"weather":
[{"id":801,"main":"Clouds","description":"few 
clouds","icon":"02d"}],"base":"stations","main":
{"temp":298.15,"pressure":1019,"humidity":23,"temp_min":298.15,"temp_ma
x":298.15},"visibility":10000,"wind":
{"speed":1.5,"deg":220},"clouds":{"all":20},"dt":1526466600,"sys":
{"type":1,"id":7226,"message":0.0032,"country":"AM","sunrise":152643
5114,"sunset":1526487120},"id":616052,"name":"Yerevan","cod":200}", 
responseCookieJar = CJ {expose = []}, responseClose' = ResponseClose}

法典：

{-# LANGUAGE DeriveGeneric     #-}
{-# LANGUAGE OverloadedStrings #-}    
module PrepareAnswer where
import           Control.Monad
import           Data.Maybe
import           GHC.Generics
import           Data.Aeson
import           Data.Aeson.Types
import qualified Data.ByteString          as BS
import qualified Data.ByteString.Lazy     as BSL
import           Data.Text
import           Network.HTTP.Client
import           Text.Read
import           Data.Text         
import           Text.JSON
import           AskWeather
data WeatherValues = WeatherValues
{ temp_min :: Double          
-- , temp_max :: Text
-- , pressure :: Text
-- , speed     :: Text
} deriving (Show) -- Здесь speed подразумевается как скорость ветра
prepareAnswer :: Response BSL.ByteString -> Text
prepareAnswer response = Data.Text.pack . show $ weatherValues
where
--finalPhrase = createFinalPrase preparedValues
--  preparedValues = prepareValues weatherValues
weatherValues = extractValues . responseBody $ response
extractValues :: BSL.ByteString -> WeatherValues
extractValues rawJSON =
let result  = decode' rawJSON
in case result of
Nothing   -> error "Invalid JSON!"
Just info -> 
let  tempMin   = getTempMin info
--       tempMax   = getTempMax   info
--      pressInfo = getPressure  info
--  windSpeed = getWindSpeed info
in WeatherValues tempMin -- tempMax pressInfo windSpeed
getTempMin :: Object -> Text
getTempMin info =
case parseMaybe extractTempMin info of 
Nothing -> "Invalid JSON!"
Just info -> info 
where
extractTempMin = info -> info .: "main"
>>=
mainInfo -> mainInfo .: "temp_min"

Answer 1

代码中的这三个片段是不可调和的：

data WeatherValues = WeatherValues
{ temp_min :: Double
}
let tempMin = getTempMin info
in WeatherValues tempMin
getTempMin :: Object -> Text

可能正确的解决方案是调整getTempMin以返回Maybe Double(也许通过以某种方式解析您提取的Text(，并调整extractValues以返回Maybe WeatherValues。