(let-class name ..clauses)
  name: a sym
  clauses: zero or more forms
  returns #n

Defines a class and binds it to a local variable.

The first time each let-class form is evaluated, it evaluates a class form, stores it in a gensymmed global variable, and also binds it to the local variable name.

Each subsequent time that it's evaluated, it takes the class stored in that global variable, and binds it to the local variable name.