🤖 AI Summary
This work proposes a novel reflective protocol that enables runtime upward navigation through the semantic tower—a capability absent in existing runtime systems, which are restricted to downward execution along abstraction layers. By formally integrating operational semantics with runtime reflection, the approach introduces the notion of “first-class implementations” and establishes a generalized safe-point mechanism grounded in formal specifications. This mechanism permits observation and dynamic switching of high-level abstractions’ underlying implementations during execution, thereby overcoming the traditional limitation of supporting only downward compilation or interpretation. The study demonstrates, for the first time, the feasibility and effectiveness of deeply integrating semantic theory with runtime system design, enabling adaptive and semantically aware execution environments.
📝 Abstract
Software exists at multiple levels of abstraction, where each more concrete level is an implementation of the more abstract level above, in a semantic tower of compilers and/or interpreters. First-class implementations are a reflection protocol to navigate this tower *at runtime*: they enable changing the underlying implementation of a computation *while it is running*. Key is a generalized notion of *safe points* that enable observing a computation at a higher-level than that at which it runs, and therefore to climb up the semantic tower, when at runtime most existing systems only ever allow but to go further down. The protocol was obtained by extracting the computational content of a formal specification for implementations and some of their properties. This approach reconciles two heretofore mutually exclusive fields: Semantics and Runtime Reflection.