• Enum : Similar to most languages, you can define names to be used in your code.  Enum labels must all start with an uppercase letter.
• Struct: Structures contain members.  A struct value contains the first member and the second member and the third member, and so on.  Structure member names begin with a lowercase letter.
• Tagged Union: Tagged unions also contain members.  A tagged union value contains the first member or the second member or the third member, and so on.  Tagged union member names begin with a lowercase letter.

Defining Types