A Hoon atom type consists of a Nock atom with two additional pieces of metadata: an aura, which is a soft type that declares if an atom is a date, a ship name, a number, etc, and an optional constant. A Hoon atom type is warm or cold based on whether or not the constant exists:
- A Hoon atom type is warm if the constant is
~(null), any atom is in the type.
- A Hoon atom type is cold if the constant is
[~ atom], its only legal value is atom.