在Elm中的声明模块之外访问联合类型 [英] Access Union Types outside of declaring module in Elm

问题描述

给出

--module 1
module Module1 exposing (Message) where

type Message
  = Test String
  | Error Int


--module 2
module Module2 exposing (sayTest, sayError) where

import Module1 exposing (Message)

sayTest : String -> Message
sayTest msg =
  Test msg  --error

sayError : Int -> Message
sayError code =
  Error code --error


processMessage : Message -> String
processMessage msg ->
  case msg of
    Test s -> s
    Error i -> toString i

如何访问 Test 和模块2中的错误？

目前，我必须在模块1中创建函数，该函数在调用时将创建

At the moment, I have to create functions in module 1 which when called will create the instances needed but as the list is getting longer, this is becoming impractical.

推荐答案

您可以公开导出的所有类型构造函数像这样输入：

You can expose all type constructors for an exported type like this:

module Module1 (Message (..)) where

或者，如果您只想导出几个类型构造函数，则可以单独将它们调出：

Alternatively, if you wanted to export only a few type constructors, you can call them out individually:

module Module1 (Message (Test, Error)) where

type Message
  = Test String
  | Error Int
  | Foo String
  | Bar

在上面的代码中，Foo和Bar构造函数对模块保持私有。

In the above code, the Foo and Bar constructors remain private to the module.

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