Making Impossible States Impossible

[Ed Ilyin]

I have watched a great talk "Making Impossible States Impossible" by Richard Feldman.

But I can't figure out how to make impossible wrong modes of pages.

Stright forward approach looks like following:

```elm

type ListView = ListView

type DetailsView = DetailsView

type PolymerElement = PolymerElement

type ElmElement = ElmElement

type Page

  = BuildingList ListView PolymerElement

  | BuildingDetails DetailsView PolymerElement

  | BulbList ListView PolymerElement

  ...

  | HorseDetails DetailsView ElmElement

```

But then I can't write a pattern to match only DetailViews to add the back button to the view.

Or match only PolymerElements to import Polymer element for specific page.

Is it possible to achieve without writing case...of of all pages multiple times in code?

[Peter Damoc]

It looks like you are duplicating knowledge. If your BuildingList can only be connected to a ListView, adding that in the type is redundant. Same with Elements.

Think in terms of: what is the minimal information that I can get in the view in order to be able to render what I need to render and model only that.

If you know that BuildingList uses a listView and Polymer, then only use BuildingList. It is sufficient.


  

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There is NO FATE, we are the creators.
blog: http://damoc.ro/