在Elm中，是否有合并合并类型的方法? (出于模块化目的) [英] In Elm, is there a way to merge union types ? (for modularity purpose)

问题描述

从这三个声明开始:

type SharedMsg
   = SharedAction

type Page1Msg
   = Page1Action

type Page2Msg
   = Page2Action

我有没有办法获得下一个的等价物?像合并"联合类型的方法一样?

I there a way to obtain an equivalent of the following one? Like a way to "merge" union types ?

type Msg
   = SharedAction
   | Page1Action
   | Page2Action

============================

=============================

上下文:我正在将Elm应用程序分成每页一个模块，每个模块都有自己的文件夹.

Context : I am splitting an Elm application into one module per page with their own folders.

某些操作将被共享，而某些操作将是特定于页面的.

Some actions will be shared, and some actions will be page-specific.

如果要使用Html.map方法，我觉得我将不得不重写页面以其自身的PageMsg消息类型使用的每个共享操作:

If I was to use the Html.map method, I feel that I would have to re-write every shared action that a page uses in its own PageMsg message type:

type Page1Msg
   = Page1Action
   | SharedAction

type Msg
   = Page1Msg Page1Msg
   | Page2Msg Page2Msg

view : Model -> Html Msg
view =
   Html.map Page1Msg (Page1View.view model)

因此，我想对所有页面使用唯一的Msg类型，但是通过在其自己的文件夹中写入特定于页面的消息来保持模块化，然后通过合并它们以某种方式定义唯一的Msg类型.

Hence my thinking of using a unique Msg type for all pages, but preserving modularity by writing page-specific messages in their own folders, and then somehow defining a unique Msg type by merging them.

推荐答案

@ z5h的答案几乎是正确的，但是类型构造函数必须具有不同的名称.

@z5h's answer is almost correct, but the type constructors have to have different names.

您无法按照自己的方式合并类型.

对于惯用方式:您将拆分类型命名为Msg，而不是Page1Msg.因此，例如:

As for the idiomatic way: You would name the split types just Msg, not Page1Msg. So, for example:

Page1.elm:

module Page1 exposing (Msg)

type Msg
  = Foo

Page2.elm:

module Page2 exposing (Msg)

type Msg
  = Bar

Shared.elm:

module Shared exposing (Msg)

type Msg
  = Baz

Main.elm:

module Main exposing (..)

import Shared
import Page1
import Page2

type Msg
  = SomethingCustom
  | SharedMsg Shared.Msg
  | Page1Msg Page1.Msg
  | Page2Msg Page2.Msg

---

顺便说一句，请记住，如果将模块分为Page1.View，Page1.Types等，则只要公开的功能不重叠，就可以使用相同的名称导入不同的模块，即:

---

By the way, remember that if you split the modules into Page1.View, Page1.Types, etc., then as long as the exposed functions don't overlap, you can import different modules under the same name, ie:

import Page1.Types as Page1
import Page1.State as Page1
import Page1.View as Page1
import Page1.Decoders as Page1

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