%dw 2.0

import every from dw::core::Arrays

// Closed object type with two properties alias and name
// that must have the String type.
type User = {|alias: String,name: String|}

// Helper function to check if argument value
// is an Array type and
// only contains elements of type String.
fun checkArrayString(value: Any): Boolean =
    (value is Array) and
    ((value as Array) every ((element) -> element is String))

// Literal type.
type Language = "DataWeave" | "Java" | "Groovy" | "Clojure"

output application/json
---
{
    string: "DataWeave" is String,
    not_string: 42 is String,

    number: 42 is Number,

    // We can also use the Null type to check.
    null_value: null is Null,

    object: {alias: "mrhaki", name: "Hubert A. Klein Ikkink"} is Object,

    // We can check on our own object type.
    user: {alias: "mrhaki", name: "Hubert"} is User,

    // Only the alias property is valid.
    not_user1: {alias: "mrhaki", firstName: "Hubert", lastName: "Klein Ikkink"} is User,

    // User is a closed object so extra properties
    // don't make it of type User anymore.
    not_user2: {alias: "mrhaki", name: "Hubert", location: "Tilburg"} is User,

    // Type of alias property is not correct.
    not_user3: {alias: 42, name: "Hubert"} is User,

    array: ["one", "two"] is Array,

    // To also check the types of the elements
    // we must use an extra check as defined
    // in the checkArrayString helper function.
    array_string: checkArrayString(["one", "two"]),
    not_array_string: checkArrayString([1, 2]),
    not_array: checkArrayString(42),

    // Literal types are supported.
    language: "DataWeave" is Language,
}

{
  "string": true,
  "not_string": false,
  "number": true,
  "null_value": true,
  "object": true,
  "user": true,
  "not_user1": false,
  "not_user2": false,
  "not_user3": false,
  "array": true,
  "array_string": true,
  "not_array_string": false,
  "not_array": false,
  "language": true
}