Programming Languages and Systems 23rd Asian Symposium, APLAS 2025, Bengaluru, India, October 27–30, 2025, Proceedings (Alex Potanin)（Z-Library）

# Programming Languages and Systems: APLAS 2025 Proceedings ## 【One-Line Pitch】 A collection of peer-reviewed research papers from the 23rd Asian Symposium on Programming Languages and Systems, covering cutting-edge work in type systems, memory safety, resource-aware computation, and formal verification—essential reading for programming language researchers, graduate students, and practitioners interested in the theoretical foundations of software systems. ## 【Book Arc】 - **Opening (~0%–3%)**: The preface establishes the symposium's scope and review process—34 submissions, double-blind review, 13 accepted papers—along with the Best Paper award going to "Memory Safety: Uniqueness as Separation." This section orients readers to the conference's mission of bridging programming language theory and practice. - **Early (~10%–23%)**: The first major paper, "Memory Safety: Uniqueness as Separation," develops a formal framework for verifying that C code imported into the Cogent language preserves memory safety guarantees. The authors introduce frame conditions (leak freedom and fresh allocation) and prove theorems connecting uniqueness types to separation logic, including a detailed treatment of the frame rule's soundness. - **Early (~29%–32%)**: The second paper introduces algebraic foundations for resource-aware computation, specifically grade monoids with subtraction—a novel structure compared to the ordered semirings typically used. This section defines the mathematical machinery needed to track resource consumption in type systems. - **Middle (~39%–42%)**: Building on the algebraic preliminaries, the paper "Fair Termination for Resource-Aware Active Objects" presents a graded type system ensuring that well-typed configurations are fairly terminating. Key results include weak termination theorems, deadlock freedom, input-lock freedom, orphan message freedom, and resource safety for active object calculi. - **Middle (~48%)**: A third paper shifts to formalized mathematics, presenting a Coq formalization of the second Fundamental Theorem of Calculus with weakened continuity hypotheses. The authors demonstrate its practical utility by computing integrals of indicator functions and developing integration by parts and substitution lemmas. ## 【Key Takeaways】 - **Uniqueness types can be verified at FFI boundaries** (Early): The Cogent framework tracks heap footprints through typing judgments, and the paper proves that imported C code preserves memory safety if it satisfies leak freedom and fresh allocation conditions—enabling safe systems programming without garbage collection. - **Weak validity in separation logic has trade-offs** (Early): While weak validity permits reasoning about programs that may error (like freeing an empty heap), it invalidates the frame rule's soundness—a critical tension the paper addresses through careful theorem development. - **Grade monoids with subtraction enable resource tracking** (Early): Unlike standard ordered semirings, this algebraic structure requires subtraction rather than multiplication, allowing type systems to model resource consumption where variables are "consumed" during evaluation. - **Fair termination is weaker than total termination but stronger than deadlock freedom** (Middle): Well-typed configurations guarantee that termination is always possible, not that it must happen—modeling processes like a barista taking an arbitrary number of orders while ensuring no deadlock, livelock, or orphan messages. - **Graded type systems can enforce resource safety** (Middle): The type system tracks required and produced actor contexts, ensuring that hold expressions never block and that all method calls eventually execute, even in potentially infinite executions. - **Formalized calculus benefits from weakened hypotheses** (Middle): The Coq formalization of the second FTC uses "continuity-within" rather than full interval continuity, making it applicable to functions like indicator functions that are only continuous on open subintervals. ## 【Reading Tips】 - **Skim the preface** (~0%–3%): It provides context on the review process and paper selection but contains no technical content—read it only to understand the symposium's scope. - **Deep-read the Cogent paper** (~10%–23%): This is the Best Paper winner and the most substantial contribution. Focus on the frame conditions (leak freedom, fresh allocation) and the FC Triple theorem, which connects uniqueness types to separation logic. The nominal sets and permutation machinery in the proofs can be skimmed on first reading. - **For the active objects paper** (~29%–42%): Start with the grade monoid definitions and the operational semantics rules, especially the variable reduction rule (vr-rs) that models resource consumption. The typing rules and termination theorems are the payoff—understand what fair termination guarantees before diving into proof details. - **The FTC formalization paper** (~48%): This is self-contained and accessible even without deep PL background. Read it as a case study in how formal verification tools handle real mathematical reasoning, particularly the clever use of weakened continuity hypotheses. - **Skip the extended proofs**: Multiple papers reference extended versions for complete proofs. The proceedings versions are sufficient for understanding contributions and results. ## 【Coverage Limits】 The excerpts cover only three of the thirteen accepted papers in detail. The remaining papers—covering topics like type systems, verification, and other programming language foundations listed in the table of contents—are not represented in this guide. ##