如何在 PureScript 中为 SimpleJSON 创建自定义解析器 Monad？

问题描述

我有以下内容，直到我尝试定义 readJSON' 为止：

newtype JSONWithErr a = JSONWithErr (Writer (Array Foreign.ForeignError) a)

derive newtype instance jsonWithErrApply :: Apply JSONWithErr
derive newtype instance jsonWithErrapplicative :: applicative JSONWithErr
derive newtype instance jsonWithErrFunctor :: Functor JSONWithErr
derive newtype instance jsonWithErrBind :: Bind JSONWithErr
derive newtype instance jsonWithErrMonad :: Monad JSONWithErr
derive newtype instance jsonWithErrTell :: MonadTell (Array Foreign.ForeignError) JSONWithErr
derive newtype instance jsonWithErrWriter :: MonadWriter (Array Foreign.ForeignError) JSONWithErr

newtype JSONParse a = JSONParse (ExceptT (NonEmptyList ForeignError) JSONWithErr a)

derive newtype instance jsonParseApply :: Apply JSONParse
derive newtype instance jsonParseapplicative :: applicative JSONParse
derive newtype instance jsonParseFunctor :: Functor JSONParse
derive newtype instance jsonParseBind :: Bind JSONParse
derive newtype instance jsonParseMonad :: Monad JSONParse
derive newtype instance jsonParseTell :: MonadTell (Array Foreign.ForeignError) JSONParse
derive newtype instance jsonParseWriter :: MonadWriter (Array Foreign.ForeignError) JSONParse
derive newtype instance jsonParseThrow :: MonadThrow (NonEmptyList ForeignError) JSONParse

generalize :: forall m a. Monad m => Identity a -> m a
generalize = unwrap >>> pure

-- type Except e = ExceptT e Identity
genExcept :: forall m e a. Monad m => ExceptT e Identity a -> ExceptT e m a
genExcept = unwrap >>> generalize >>> ExceptT

readJSON' :: forall a. JSON.ReadForeign a => String -> JSONParse a
readJSON' s = JSONParse $ genExcept $ (pure >>> JSONWithErr) <$> (JSON.readJSON' s) -}

这里的错误涵盖了 readJSON' 的整个定义，是：

Could not match type

    JSONWithErr t2

  with type

    a0


while trying to match type JSONParse t1
  with type JSONParse a0
while checking that expression (apply JSONParse) ((apply genExcept) ((map (...)) (readJSON' s)))
  has type JSONParse a0
in value declaration readJSON'

where a0 is a rigid type variable
        bound at (line 0,column 0 - line 0,column 0)
      t1 is an unkNown type
      t2 is an unkNown type

我试图简化它，但我似乎遇到了约束问题；在下面的简化中，键入的孔由于较早的错误而不起作用：

tmp :: forall a. JSON.ReadForeign a => String -> ExceptT (NonEmptyList ForeignError) JSONWithErr a
tmp s = ?help (JSON.readJSON' s)

和错误：

  No type class instance was found for

    Simple.JSON.ReadForeign t0

  The instance head contains unkNown type variables. Consider adding a type annotation.

while applying a function readJSON'
  of type ReadForeign t0 => String -> ExceptT (NonEmptyList ForeignError) Identity t0
  to argument s
while inferring the type of readJSON' s
in value declaration tmp

解决方法

暂无找到可以解决该程序问题的有效方法，小编努力寻找整理中！

如果你已经找到好的解决方法，欢迎将解决方案带上本链接一起发送给小编。

小编邮箱:dio#foxmail.com (将#修改为@）