Hi Fernando. Thanks for your input! A few things:
1. Why can't you just do this:
type Action = LoginOut | EventAction Events
i.e. you create a new tag for Action that lets you use an Events
2. Do you know how this will affect type inference? Elm's type system is
nearly maximal, in the sense that adding features usually breaks inference.
This almost certainly will, since it introduces subtyping. Look at this
example:
case x of
Increment -> 3
_ -> 0
What is the type of x? In Elm, we can tell from the tag that it's an event.
Here, we can't tell if it's an Event or an Action. We'd then need some
notion of a subtype, which usually doesn't play well with inference. I
don't know if this flavour of subtyping is undecidable, but my gut says it
is.
3. You should probably follow these threads on Elm-dev:
https://groups.google.com/forum/#!topic/elm-dev/klu1gg7Snwk
https://groups.google.com/forum/#!topic/elm-dev/B3knsc7tv50
On Sat, Aug 6, 2016 at 8:57 AM, Fernando J. Naranjo Talavera <
[email protected]> wrote:
> Hello everyone.
> I have been experimenting with Elm language for some weeks now, mainly in
> the areas of Styling and Composition.
> In all this time I have been struggling to find a suitable solution for
> Composition and Separation of concerns in Elm when it comes to Medium /
> Large projects.
> Sadly, what I have found is that (the in all the other respects
> *excellent*) Elm type system and architecture, always stands in my way.
>
>
> I have pushed a really small Elm project to GitHub in which I have tried
> to settle what (IMHO) would be an interesting addition to the Elm language:
> The ability to Combine/Compose Union Types (not individual Tags)
>
> https://github.com/fejnartal/elm-utcombination
>
> This project is so tiny that, I believe, everyone should be able to take a
> look a understand the kind of flexibility I'm trying to pursue.
> So I would be very glad to hear your suggestions.
>
> - If you believe the language is already able to account for the kind of
> abstraction I'm trying to build PLEASE, I would be very grateful to hear
> about your approach to this problem.
> - If you think you would end up using such a feature, that would be great
> news. And also, any suggestions or drawbacks that you may have identified
> in t he proposal.
> - Whatever you have to say. Thanks.
>
> All my career, I have been mostly an Object Oriented programmer and it's
> only now that I'm beginning to learn and practice with functional
> languages. So, it's quite possible that my OO mindset may be reflected in
> the code.
>
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