JSON

Json is an opaque host-backed standard-library type. Programs construct and inspect it through the Json module rather than relying on JavaScript object representation.

Construct JSON values

The module provides constructors for every JSON shape:

func document() -> Json do
  Json.object([
    ("name", Json.string("Noodle")),
    ("count", Json.int(3)),
    ("active", Json.bool(true)),
    ("tags", Json.array([Json.string("typed"), Json.string("modular")])),
    ("extra", Json.null()),
  ])
end

Json.number accepts Double; Json.int preserves the convenient explicit integer boundary. Object entries are supplied as an array of (String, Json) tuples.

Parse and stringify

Json.parse(text) returns Result[Json, String]; the error string describes invalid JSON input. Json.stringify(value) returns compact JSON text:

func normalize(text : String) -> Result[String, String] do
  switch Json.parse(text)
  case Result::Ok(value) then Result::Ok(Json.stringify(value))
  case Result::Err(message) then Result::Err(message)
  end
end

This example handles the Result explicitly. A throws wrapper can propagate a declared error type when the application wants a domain-specific failure contract.

Inspect through JsonView

JsonView presents the opaque host value as one of six datatype constructors: Null, Bool, Num, Str, Arr, or Obj.

func describe(value : Json) -> String do
  switch value
  case Json.JsonView::Null then "null"
  case Json.JsonView::Bool(flag) then flag.to_string()
  case Json.JsonView::Num(number) then number.to_string()
  case Json.JsonView::Str(text) then text
  case Json.JsonView::Arr(items) then
    "array(" ++ items.length().to_string() ++ ")"
  case Json.JsonView::Obj(object) then
    "object(" ++ object.entries().length().to_string() ++ ")"
  end
end

This is a view pattern: the associated IView provider converts the opaque Json target once and the ordinary datatype pattern matches the resulting shape. View pattern behavior builds on Interfaces and extensions, Advanced pattern matching for the complete view-pattern rules.

JsonObject.field(name) returns Option[Json]; entries() returns the object’s entries as an array.

Next: Output, debugging, and tests.