Builtin classes

The runtime MUST provide the following classes:

Class	Description
term	Contains everything, all other classes are subsets of this one
atom	Contains all atoms (ie. @ok, @error, ...)
bool	Contains true and false
number	Contains all numbers (ie. 1, 2.3, ...)
int	Contains all integers, it is a subset of number
string	Contains all strings (ie. "hello world")
list<T>	Contains all lists where their elements are of class T
proplist<T>	Contains all lists where their elements are of class (atom, T)
pid	Opaque class that contains all process identifiers
iocap	Opaque class that contains all IO capabilities

Each Letlang value is also a singleton type, the runtime MUST provide an implementation for such types.

The runtime MUST provide an implementation for tuple types and named tuple types.