如何在JSON中表示变体（sum-types）？

Algebraic data types are the convenient way to accurately describe the data. There is no problem with product-types in JSON. However it's not clear what a sum-type can be, so how can I represent a variant type in JSON?

代数数据类型是准确描述数据的便捷方式。 JSON中的产品类型没有问题。但是,不清楚sum-type是什么,所以如何在JSON中表示变体类型?

2 个解决方案

#1

Perhaps using object notation with value and tag properties? E.g.:

也许使用带有值和标签属性的对象表示法?例如。:

{
    "someVariant": {
        "value": 25,
        "tag":   "currentFormOfTheVariant"
    }
}

Object and specially-formatted strings are basically your only real options for self-describing data types in JSON.

对象和特殊格式的字符串基本上是您在JSON中自描述数据类型的唯一实际选项。

#2

Take for example the following variant type.

例如,以下变体类型。

data Tree = Empty
          | Leaf Int
          | Node Tree Tree

In JSON you can use the following three forms to specify the three variants.

在JSON中,您可以使用以下三种形式来指定三种变体。

Variant | JSON
--------+---------------
Empty   | null
--------+---------------
Leaf    | {
        |   "leaf": 7
        | }
--------+---------------
Node    | {
        |   "node": [
        |     <tree>,
        |     <tree>
        |   ]
        | }

Basically, use a JSON object with a single key-value pair, where the key is the selected variant.

基本上,使用具有单个键值对的JSON对象,其中键是选定的变体。

#1