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?
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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