10-01: Static vs. Dynamic Typing

• The dynamic type of an object is the class C that is used in the “new C” expression that created it;
• The static type of an expression captures all dynamic types the expression could have;
• Soundness theorem: for all expressions E: dynamic_type(E) = static_type(E).

11-03: Activation Records

The information needed to manage one procedure activation is called an activation record (AR) or frame.

11-06: Stack Machines

1. Only storage is a stack;
2. An instruction $r = F(a_1 ... a_n):$
   • Pops n operands from the stack;
   • Computes the operation F using the operands;
   • Pushes the result r on the stack.
3. An n-register stack machine:
   • Conceptually, keep the top n locations of the pure stack machine’s stack in registers.
4. Consider a 1-register stack machine:
   • The register is called the accumulator.
5. Algorithm:
   • Consider an expression $op(e_1 ... e_n)$:
     1. Note $e_1 ... e_n$ are subexpressions.
   • For each $e_{i(0 < i < n)}$:
     1. Compute $e_i$;
     2. Push result on the stack.
   • Pop n - 1 values from the stack, compute op;
   • Store result in the accumulator.