How to use the @as decorator?

#1

I am experimenting with the @as decorator with the following code:

type status = [
  @as("GOOD") #Good |
  @as("BAD") #Bad
]

@val external setStatus: status => unit = "setStatus"

setStatus(#Good)

This compiles to:

setStatus("Good");

But I was expecting it would compile to:

setStatus("GOOD");

I suspect I am not using the decorator correctly. Any suggestions on how to correct this?

View in playground

Thanks

#2

After some more investigation I’ve discovered this:

@val external setStatus: @string[
  @as("GOOD") #Good |
  @as("BAD") #Bad
] => unit = "setStatus"

setStatus(#Good)

Which produces:

setStatus("GOOD");

So it seems that:

  1. It’s intended for use with externals, and
  2. the @string decorator is also required.

How does that sound?

Update:

Some more investigation, I see it can be used with record types as well.

type action = {@as("type") type_: string}

let one: action = {type_: "One"}

which produces:

var one = {
  type: "One"
};

So it seems, that the @as decorator:

  1. may be used with record types directly, and
  2. may be used with polymorphic variants on externals with the @string or @int decorators.

How does that sound?

#3

Your two statements are correct.

Poly vars are more flexible with the identifier names for its constructors, so you can easily do it without the as decorator as well, e.g. #GOOD.

Docs on poly vars are currently in the last review phase, so hopefully this will be more clear in the future!

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