CMP.12:11 - SoTA-Echoing

How should expression meaning become executable? Adopt the constructor-based evaluation and saved-environment application in SICP’s evaluator for :4.2–4.3. Its historical contribution is exposing operations otherwise hidden in a host language. A direct evaluator is a serious cheaper choice for changing or infrequently executed expressions. Adapt SICP’s compilation construction when prior analysis repays its cost over subsequent runs: construct operations instead of repeatedly selecting them during execution. Keep binding and control semantics while comparing conversion, code storage and later execution. A changed execution frequency, primitive or language feature reopens that choice.

Which preservation claim supports actual reuse? Adopt the explicit behavioral scope in the current CompCert manual, section 1.2, for :4.1 and :4.5. Matching final values is sufficient only for uses governed by those values; interaction and termination can require more. CompCert’s theorem has its own language-defined behavior and undefined-behavior treatment, and excludes time and memory consumption from its observed trace. A translator for a language with a defined division error therefore needs the error policy chosen in :5.3, not an imported C-specific permission to remove it. A changed observation or admitted execution context reopens the relation.

For larger compositions, adapt the choice between operational simulation and denotational behavioral refinement examined in Denotation-based Compositional Compiler Verification. The latter uses algebraic composition of behavioral sets to reduce proof duplication, while retaining termination, divergence, failure and interaction distinctions that simpler final-state accounts can lose. Use it when those operations fit the language and simplify the actual preservation argument; a direct structural or state correspondence remains sufficient for the small constructions here. Neither proof representation automatically supplies a cheaper compiler. Changed control features, module interaction or proof-maintenance cost can reverse the selection.