(int) Defined(variable)
If a variable is referenced before it is assigned to, the variable has
no type, but behaves in all ways as a string set to the variable's
name. This function returns 1 if the argument has a type assigned, or
0 if it has no type.
(string) TypeOf(variable)
This function returns a string which indicates the type of variable
passed as an argument. The possible returns are