AMP Access expression grammar

[carlosabalde]

I would like to clarify a couple of simple questions about the AMP Access expression grammar:

• Are dots, dashes and/or underscores allowed in the names of properties returned by the AMP Access authorization endpoint? The expression grammar is slightly ambiguous about this.
• Are string comparisons allowed in AMP Access expressions?

[dvoytenko]

@carlosabalde a more complete grammar is here: https://github.com/ampproject/amphtml/blob/master/extensions/amp-access/0.1/access-expr-impl.jison

Are dots, dashes and/or underscores allowed in the names of properties returned by the AMP Access authorization endpoint?

No, dots, dashes or underscores allowed. Underscores is rather unfortunate and I will fix it asap. But I think dots and dashes will not be allowed.

[dvoytenko]

@carlosabalde

Are string comparisons allowed in AMP Access expressions?

Yes.

field = 'abc'
field != 'abc'

[dvoytenko]

I updated the grammar. Names now allow underscore.

[jugglingcats]

Is there a reason nested objects are not allowed, eg.

field: { prop1:'value' }

Sometimes an access decision can contain quite complex information needed to message the user, and flattening this into name value pairs is restrictive.

[dvoytenko]

No strong reason, no. Mostly it's meant to insist on simpler structures given that the authorization response is free-form and designed specifically for the needs of access. And we'd definitely like to limit the depth, e.g. to only the depth of 1 (object.field). Do you see it really needed? Could you share an example or two?

[jugglingcats]

Thanks for reply. A metering response might look like this:

{
  "action": "login",
  "exceededMeter": {
   "period": "WEEKLY",
   "max": "10"
  },
  "authenticatedMeter" {
   "period": "WEEKLY",
   "max": "20"
  }
}

In some cases complex messaging would be left to the login page, but you can imagine using amp-mustache directly to render a message like:

You have exceeded your meter count of 10 articles per week.
But you can get up to 20 articles per week by registering.
Register or sign in now to read this article!

Obviously the data can be flattened but this is not very scalable.

[dvoytenko]

Sounds good. I moved the request to #1919