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Discussion on: The basic Elm example that I wish I'd had

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kwitgit profile image
kwitgit

Also, looking at it more carefully... how is the top-level DisplayingRoom type defined? I'm sure that's a ridiculously basic question...

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nimmo profile image
Nimmo • Edited

Ah I think my wording has probably confused matters - Model is the custom type, DisplayingRoom and Failure are values that custom type can have. (These are known as type variants)

DoorState and AlarmState are also custom types.

This might help clarify things a little:

Consider Bool - that is a type that can have a value of either True or False, and would be represented (and I imagine probably actually is represented in the source code!) as:

type Bool 
  = True
  | False

Does that answer your question? :)

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kwitgit profile image
kwitgit

Ooohh yes, that makes perfect sense! A custom type can have any... custom... values you make up, they don't have to be defined separately anywhere else. I get it now. My mental block was that I was still thinking of the Model type as a record, just because it was named Model. LOL.

I guess I'm starting to see why "custom types" is a better name than "union types" (what they used to be in 0.18). Thanks for the update to 0.19!

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nimmo profile image
Nimmo

Glad that helped! I can totally see how that caused confusion.

And yeah, I think the change of naming convention from union to custom is a big positive. Custom type is a phrase that can be easily understood without even having any real understanding of the language at all! :)