Module exposing in Elm 0.18

Question

I have an elm module of Types that consists of types and type aliases Foo, Bar and Baz. When I export everything like so, the code works:

module Types exposing (..)

However, if I include all of the types explicitly, the code breaks.

module Types exposing (Foo, Bar, Baz)

This is also true of the import statements on the consuming file; both need to be exposing (..)

What is the difference between these two approaches?

Answer 1

I'm only learning Elm myself very recently but it sounds like since one of your types (Msg) is being defined as a union type that you will need to use the Msg(..) syntax when exporting this type.

module Types exposing (Msg (..))

type Msg = FirstAction | SecondAction | ThirdAction

Or in the case of importing the union type.

import Types exposing (Msg (..))

Please see GitHub issue #968 for an explanation of why this is required for union types.