Matt Moore's 15-312 Recitation Outline 9/29/2004

Things to specify when adding a new type to a language:
 - values and how to evaluate (Dynamic Semantics)
 - typing rules (Static Semantics)
   - Constructors and Destructors
     - Constructor: When the *result* of applying the rule is something of the new type
     - Destructor: When you are "looking inside" something of the given type, and using its data to perform some task
 - value inversion cases

Reason for structuring our language design this way:
 - Since everything is given in rule form, when we make a language extension, since all we are doing is adding new rules, to re-prove Progress and Preservation, we need only extend our previous proof with these cases.

Example: Binary Trees:
 - Static Semantics: (point out constructors/destructor)
 - Dynamic Semantics: (values / stepping rules)
   - value inversion case(s)
 - Preservation Proof
 - Progress Proof