Finds the nested data structure type from a Game Maker list.

ds_list_get_type.gml

/// @desc Returns the type of data structure nested at an index of a ds_list.
/// @param id {Integer} The id of the ds_list to consider.
/// @param pos {Integer} The index of the ds_list to inspect.
/// @author Kat @katsaii
if (is_real(argument0[| argument1])) {
    // copy the ds_list into a duplicate list that can be manipulated freely
    var clone = ds_list_create();
    ds_list_copy(json_list, argument0);
    // delete all records other than what's required
    repeat (argument1) {
        // trim the left hand side of the list
        json_list[| 0] = noone;
        /* This prevents nested structures from being deleted when we remove
         * the record from the cloned map.
         */
        ds_list_delete(json_list, 0);
    }
    repeat (ds_list_size(json_list) - 1) {
        // trim the right hand side of the list
        json_list[| 1] = noone; // see above
        ds_list_delete(json_list,1);
    }
    // encode the final json and free dynamic structures
    var obj = ds_map_create();
    ds_map_add_list(obj, "list", clone);
    var context = json_encode(obj);
    clone[| 0] = noone; // see above
    ds_map_destroy(obj);
    // use the json string to determine the type of the value contained
    var trim_start = string_pos("[", context) + 2;
    var trim_end = string_length(context) - 3;
    var trimmed = string_copy(context,
            trim_start,
            trim_end - trim_start);
    switch (string_char_at(trimmed, 1)) {
    // the first character is enough information to infer the type of structure
    case "[":
        return ds_type_list;
        break;
    case "{":
        return ds_type_map;
        break;
    }
}
// if the key is not real, there is no chance of it being a data structure
return -1;