Question

我的sum数据类型如下所示：

data Declaration =
    IndDecl { what :: String, name :: String, argnames :: Maybe [String], constructors :: [Constructor] }
    | TypeDecl { what :: String, name :: String, argnames :: Maybe [String], value :: Maybe Arg }
    | FixDecl { what :: String, fixlist :: Maybe [Fixitem] }
    | TermDecl { what :: String, name :: String, typ :: Maybe Typ, value :: Maybe Arg }
    deriving (Show, Eq)

我正在使用Data.Aeson.TH使用以下选项派生JSON序列化器/解串器：

$(deriveJSON defaultOptions { sumEncoding = UntaggedValue } ''Declaration)

从JSON构造中删除标记。同时，我认为我的数据已经有一个标记，即what字段。它可以是以下之一：

IndDecl : "decl:ind" 
FixDecl : "decl:fix"

等。因此，我对我的JSON反序列化对象使用Untagged配置这一事实令人担忧。如何使Aeson根据我的数据已有的标记派生JSON存根？

或者最好删除what字段并让Aeson添加一个描述构造函数的“tag”字段？

编辑：我通过添加标记字段来尝试后者。现在看起来像：

-- Declarations
data Declaration =
    IndDecl { what :: String, tag :: String, name :: String, argnames :: Maybe [String], constructors :: [Constructor] }
    | TypeDecl { what :: String, tag :: String, name :: String, argnames :: Maybe [String], value :: Maybe Arg }
    | FixDecl { what :: String, tag :: String, fixlist :: Maybe [Fixitem] }
    | TermDecl { what :: String, tag :: String, name :: String, typ :: Maybe Typ, value :: Maybe Arg }
    deriving (Show, Eq)

但是，我收到以下错误：

$ .declarations [0]出错：键“tag”不存在

我不明白，因为我创建了一个“标记”字段。

带总和类型的Haskell Aeson

0 个答案: