Cannot expose UnionType

Question

I have two elm modules trying to share a union type as I try to refactor my app as described here https://www.elm-tutorial.org/en-v01/02-elm-arch/07-composing-2.html but I keep getting

does not expose

even though I have tried to model it as in https://github.com/elm/elm-lang.org/issues/523

Module 1

module Module1 exposing ( OneMsg(..), Model, view, [etc.] )

...

type OneMsg
    = Name String 

...

Module 2

module Module2 exposing(..)

import Module1 exposing(OneMsg(..))


type Msg
    = UrlChange Navigation.Location 
    | ...
    | Module1Msg Module1.OneMsg

...

Html.map Module1.OneMsg (Module1.view model)

...

Getting this error

   -- NAMING ERROR ---------------------------------------------- ././view/View.elm

   Cannot find variable `Module1.OneMsg`.

   74|                     Html.map Module1.OneMsg (Module1.view model)
                                    ^^^^^^^^^^^^^^^^^^
   `Module1` does not expose `OneMsg`.

Only thing I found here is an old questions which seems to be the same event though an old syntax: Access Union Types outside of declaring module in Elm

In case relevant I use elm 0.18.0.

Bet I just missed something. Can any one spot the problem?

Answer 1

Module1.OneMsg is a type. Html.map expects a function as its first parameter. The way you typically bubble up messages would be something like this (in Module2):

type Module2Msg
    = ...
    | Module1Msg Module1.OneMsg

And then you could use it like this in Module2:

Html.map Module1Msg (Module1.view model)