15-851 Computation and Deduction
Lecture 2: Natural Semantics

We define the operational semantics of Mini-ML by a set of inference rules that allow us to establish the relation between an expression and its value. This style of definition we follow is called natural semantics. We then use this definition to establish our first meta-theorem, namely that the result of evaluation (if it exists) is in fact a value. The techniques we use will be with us for the rest of the course, namely structural induction and inversion.

We also define the typing rules for Mini-ML that sort out valid from invalid expressions in preparation for the type preservation theorem in the next lecture.

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Frank Pfenning