Default Values

Several Frost types have a default value:

* All `Int`s, `Real`s, and `Char`: `0`
* `Bit`: `false`
* Nullable types: `null`

Fields in a newly-created object are initialized to their default value prior to the init method's execution. Non-nullable types other than those listed above do not have a default value; you may not read such fields before they are assigned, and they must be initialized prior to invoking the superclass init method.