SU-CS143 MAY152025 — Jemoka Knowledge Base

“If B is a subclass of A, then an object of B can be used wherever A is expected.” To do this, we will lay out: the pointer * points to a method table Other Semantics than structural operational semantics denotational semantics axiomatic semantics Runtime Errors We have to catch some runtime errors: calling on voids method dispatch problems What to track in context? environment: where in memory a variable is stored? Map<Symbol, void *> store: what is in memory? Map<void *, Value> This means that a judgment is:

\begin{equation} \text{self}, E, S \vdash e: V, S' \end{equation}

that is, “given environment E, store S, we have that e evaluates to V, and S are side effects.” The reason why environments doesn’t change is because we can’t pass globals up, so scoping always travels down. assignments As you would expect:

\begin{equation} \frac{so,E, S \vdash e : v, S_1 | E\left(id\right) = I_{id} | S_2=S_1[v / I_{id}]}{so, E, S \vdash id \leftarrow e: v, S_2} \end{equation}

Notice! we have side effects that are CHAINED; if evaluating e has side effects, we carry them into our evaluation in the side effects S \to S_1 \to S_2. loops We use recursion!

\begin{equation} \frac{\begin{align}&so, E, S \vdash e_1: true, S_1 \\ &so, E, S_1, \vdash S_2 : v, S_2 \\ &so, E, S_2 \vdash \text{ while } e_1 \text{ loop } e_2 \text{ pool } : void, S_3\end{align}}{so, E, S \vdash \text{ while } e_1 \text{ loop } e_2 \text{ pool } : void, S_3} \end{equation}

how do we allocate new spaces? We can use the syntax

\begin{align} &l_{new} = \text{newloc}\left(S_1\right) \\ &so, E[l_{new} / id], S_1[v_1 / l_{new}] \vdash \dots \end{align}

how do we allocate new objects? …what about self? \begin{equation} \frac{}{\text{so}, E, S \vdash \text{self}: \text{so}, S} \end{equation} errors to check dispatch on void division by zero substring out of range heap overflow generally we need to exit gracefully