Recursive type definition (tree structure)

[osamimi]

Does pkl support recursive / tree-like structures like one can achieve with json schema { "$ref": "#" } syntax.
Something like : typealias NestedParam = Mapping<String, Param | NestedParam>
See example below.

schema.pkl:

class Param {
  val: Int | Float
  signed: Boolean = true
}

// doesn't work
// typealias NestedParam = Mapping<String, Param | NestedParam>

class TopConfig {
    module_name : String
    params : Mapping<String, Param> // would like to use NestedParam as the type here 
}

config.pkl:

import "schema.pkl"

k = new schema.TopConfig {
  module_name = "parent"

  params {
    ["inw"] { val = params["iniw"].val + params["iniw"].val }
    ["iniw"] { val = 1 }
    ["inqw"] { val = 23 }

    ["submodule1"] { // fails type-check
      ["iniw"] { val = 1 }
      ["inqw"] { val = 23 }
    }
  }
}

[HT154]

Pkl does not currently allow recursive type aliases (see previous discussion in #268)

[bioball]

Note: we'd like to support recursive typealiases in the future.