JSON Parser only outputs "null" values when using variables in strings

[add-n2x]

Describe the bug
The new Liquidsoap 2.1 JSON Parser doesn't work when including variables in strings.

To Reproduce

Scenario 1: Doesn't work

let json.parse data = '{"show_id": "-1", "show_name": "Random Music"}'
print("Set current show to '#{data.show_name}' (ID: #{data.show_id})")

# > Set current show to 'null' (ID: null)

Scenario 2: Works

let json.parse data = '{"show_id": "-1", "show_name": "Random Music"}'
print("Set current show to '" ^ data.show_name ^ "' (ID: " ^ data.show_id ^ ")")

# > Set current show to 'Random Music' (ID: -1)

Scenario 3: Works, when properties have been accessed before using a var string

let json.parse data = '{"show_id": "-1", "show_name": "Random Music"}'
print("Set current show to '" ^ data.show_name ^ "' (ID: " ^ data.show_id ^ ")")
print("Set current show to '#{data.show_name}' (ID: #{data.show_id})")

# > Set current show to 'Random Music' (ID: -1)
# > Set current show to 'Random Music' (ID: -1)

Expected behavior

Scenario 1.) would print Set current show to 'Random Music' (ID: -1)

Version details

• OS: Ubuntu 21.10
• Liquidsoap 2.1.x - rolling release

Install method

• Rolling release, Debian package

[toots]

Thanks for trying the new parser!

This behavior is unfortunately expected and explained in the documentation: https://www.liquidsoap.info/doc-dev/json.html

The reason is that the string interpolation #{..} does not force its content to be a string because all values can be converted to string in liquidsoap (yey polymorphism madness).

The recommended way to parse JSON should always be with an associated type annotation:

let json.parse data : { show_id: string, show_name: string } = '{"show_id": "-1", "show_name": "Random Music"}'

Or, even:

let json.parse { show_id, show_name } : { show_id: string, show_name: string } = '{"show_id": "-1", "show_name": "Random Music"}'

I'm gonna add a warning when parsing w/o type annotation so that is clear to the user. Thanks for reporting!

[add-n2x]

Got ya! Thanks for the quick reply.

[add-n2x]

Still, when trying your example

let json.parse data : { show_id: string, show_name: string } = '{"show_id": "-1", "show_name": "Random Music"}'

I get:

At test_parse_json.liq, line 32, char 20:
let json.parse data : { show_id: string, show_name: string } = '{"show_id": "-1", "show_name": "Random Music"}'

Error 2: Parse error

highlighting the first ":" colon as source of error.

[toots]

You need parenthesis:

let json.parse (data : {
  show_id: string,
  show_name: string
}) = '{"show_id": "-1", "show_name": "Random Music"}'

[toots]

BTW we have a rudimentary JS runtime for testing these things now! Here: https://www.liquidsoap.info/try/

[add-n2x]

With parenthesis it does indeed work. Thanks.

BTW we have a rudimentary JS runtime for testing these things now! Here: https://www.liquidsoap.info/try/

Oh wow, that's really handy. Great to see you come up with additional tooling. :-)