用Haskell Aeson解析数组 [英] Parsing an Array with Haskell Aeson

问题描述

  {series：[[1,2]，[2] ，3]，[3,4]]} 
  

我想将其解析为一组数据类型：

  data Series = Series [DataPoint] 
 data DataPoint = DataPoint Int Int  -  x和y 
  

我有很多问题试图写 FromJSON b

$ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $

我试过使用Lens来破坏DataPoint记录，但它不能编译：

  case a ^ .. values。 _的整数 - } 
 [x，y]  - > DataPoint< $> x * y 
 _  - > mzero 
  

这个错误会失败（前两行我甚至没有镜头诡计，只是尝试创建 DataPoint< $> 1> 2< / code>）：



 无法匹配类型'aeson-0.7.0.6：Data.Aeson.Types.Internal.Parser 
整数'
'整数'
预期类型：（aeson- 0.7.0.6:Data.Aeson.Types.Internal.Parser 
整数
  - >常量
（Data.Monoid.Endo 
 [aeson-0.7.0.6：Data.Aeson .Types.Internal.Parse 
（aeson-0.7.0.6：Data.Aeson.Types.Internal.Parser I 
  - >值
  - > Const 
（Data。 Monoid.Endo 
 [aeson-0.7.0.6：Data.Aeson.Types.Internal.Parser 
值
实际类型：（整数
  - >常量
 （Data.Monoid.Endo 
 [aeson-0.7.0.6：Data.Aeson.Types.Internal.Parse 
 Integer] 
  - >价值
  - > Const。
（Data.Monoid.Endo 
 [aeson-0.7.0.6：Data.Aeson.Types.Internal.Parser 
 Value 
在'（。）'的第二个参数中， ，'_Integer'
在'（^ ..）'的第二个参数中，即'values。_Integer'
  

有没有更好的方法来做到这一点？



有没有人解析数组值变成更详细的结构？ 处理向量。



  { - ＃LANGUAGE LambdaCase＃ - } 
导入Data.Aeson 
 
 data Series = Series [DataPoint] 
 data DataPoint = DataPoint Int Int 
 
 instance FromJSON DataPoint where 
 parseJSON jsn = do 
 [x，y]< -  parseJSON jsn 
返回$ DataPoint xy 
 
实例FromJSON系列其中
 parseJSON = \ case 
 Object o  - > （o。：series）>> = fmap Series。 parseJSON 
 x  - >失败$意外的json：++显示x 
  




I have a JSON doc that looks like:

{ "series": [[1,2], [2,3], [3,4]] }

I'd like to parse this into a set of data types:

data Series = Series [DataPoint]
data DataPoint = DataPoint Int Int  -- x and y

I'm having lots of problems trying to write the FromJSON instance for DataPoint.

instance FromJSON DataPoint where
  parseJSON (Array a) = ???

I've tried using Lens to destruct the DataPoint record, but it doesn't compile:

case a ^.. values . _Integer of -}
  [x,y] -> DataPoint <$> x <*> y
  _     -> mzero

That fails with this error (the first two lines I get even absent the lens trickery, just trying to create a DataPoint <$> 1 <*> 2):

Couldn't match type ‘aeson-0.7.0.6:Data.Aeson.Types.Internal.Parser
                       Integer’
              with ‘Integer’
Expected type: (aeson-0.7.0.6:Data.Aeson.Types.Internal.Parser
                  Integer
                -> Const
                     (Data.Monoid.Endo
                        [aeson-0.7.0.6:Data.Aeson.Types.Internal.Parse
                     (aeson-0.7.0.6:Data.Aeson.Types.Internal.Parser I
               -> Value
               -> Const
                    (Data.Monoid.Endo
                       [aeson-0.7.0.6:Data.Aeson.Types.Internal.Parser
                    Value
  Actual type: (Integer
                -> Const
                     (Data.Monoid.Endo
                        [aeson-0.7.0.6:Data.Aeson.Types.Internal.Parse
                     Integer)
               -> Value
               -> Const
                    (Data.Monoid.Endo
                       [aeson-0.7.0.6:Data.Aeson.Types.Internal.Parser
                    Value
In the second argument of ‘(.)’, namely ‘_Integer’
In the second argument of ‘(^..)’, namely ‘values . _Integer’

Is there a better way to do this?

Does anybody have an example of parsing arrays of values into a more detailed structure?

解决方案

Aeson have instance for list, so I think it is not necessary to deal with vectors.

{-# LANGUAGE LambdaCase #-}
import Data.Aeson

data Series = Series [DataPoint]
data DataPoint = DataPoint Int Int

instance FromJSON DataPoint where
  parseJSON jsn = do
    [x,y] <- parseJSON jsn
    return $ DataPoint x y

instance FromJSON Series where
  parseJSON = \case
    Object o -> (o .: "series") >>= fmap Series . parseJSON
    x -> fail $ "unexpected json: " ++ show x

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