json.vala

// valac --thread --pkg json-glib-1.0 json.vala
using Json;

int main(string[] args) {

    size_t length;
    string json;
    string[] std_fields = {
        "param1", "param2", "param3",
        "param4", "param5", "param6"
    };

    // Start a Generator and setup some fields for it
    var gen = new Generator();
    var root = new Json.Node(NodeType.OBJECT);
    var object = new Json.Object();
    root.set_object(object);
    gen.set_root(root);

    var value3 = new Json.Object();

    object.set_string_member("key1", "value1");
    object.set_string_member("key2", "value2");
    object.set_object_member("key3", value3);

    var fields = new Json.Array();
    foreach(string s in std_fields) {
       fields.add_string_element(s);
    }
    value3.set_array_member("key4", fields);

    json = gen.to_data(out length);
    stdout.printf(@"$json\n");

    return 0;
}