### References and pointers

[
 Datatype references
 Funcon   reference
 Type     pointers
 Funcon   pointer-null
 Funcon   dereference
]


Meta-variables
 T <: values


Datatype
 references(T) ::= reference(_:T)


Datatype
 pointers(T) ::= pointer-null | { _:references(T) }


Funcon
  dereference(_:pointers(T)) : =>(T)?
Rule
 dereference(reference(V:T)) ~> V
Rule
  dereference(pointer-null) ~> ( )