Statically enforcing safe resource management is challenging due to tensions between flexible lifetime dis-ciplines and expressive sharing patterns. Region-based systems offer lexically scoped regions under a stack discipline, wherein resources are managed in bulk. In many such systems, however, resources are second-class and can neither escape their scope nor be freely returned from functions. Ownership and linear type systems, such as Rust, offer first-class, non-lexical lifetimes with robust static guarantees, but rely on invariants that limit higher-order patterns and expressive sharing. In this work, we propose a type system that uniformly treats all heap-allocated resources under diverse lifetime, granularity, and sharing settings. Our system provides programmers with three allocation modes: (1) fresh allocation for first-class, non-lexical resources; (2) fresh allocation for second-class resources with lexically bounded lifetimes; and (3) coallocation that groups resources by shadow arenas for bulk tracking and deallocation. Regardless of mode, resources are represented uniformly at the type level, supporting generic abstraction and preserving the higher-order parametric nature of the language. Obtaining static safety in higher-order languages with flexible sharing is nontrivial. To address this, our solution builds on reachability types, and our extension adds the capability to track both individual and grouped resources, enables the expression of cyclic store structures, and allows the selective enforcing of stack lifetime discipline. These mechanisms are formalized in the A < : ∗ and { A } < : ∗ type systems, which are proven type safe and memory safe in Rocq.

Managing stateful resources safely and expressively is a longstanding challenge in programming languages, especially in the presence of aliasing. For example, scope-based constructs like Java’s synchronized blocks offer ease of reasoning, but they restrict expressiveness and parallelism. Conversely, imperative, flow-sensitive approaches enable fine-grained control, but they require sophisticated typestate analyses and often burden programmers with explicit state tracking. In this work, we present a novel approach that unifies the ease of scoped reasoning with the expressiveness of imperative typestate management. Our design extends traditional flow-insensitive capability mechanisms to a flow-sensitive setting. In particular, we decouple capability lifetimes from lexical scopes, allowing functions to receive, revoke, or return capabilities in a flow-sensitive manner, building on existing mechanisms for the safety and ergonomics of scoped capability programming. We implement our approach as an extension to the Scala 3 compiler, leveraging path-dependent types and implicit resolution to enable concise, statically safe, and expressive typestate programming. Our prototype generically supports a wide range of patterns, including file operations, advanced locking protocols, DOM construction, and session types, showing that expressive and safe typestate management can be achieved with minimal extensions to an existing language with capability support.

Reasoning about programs in the presence of mutation and aliasing is notoriously difficult. Rust has popularized lifetime-based ownership tracking in systems programming, but its “shared XOR mutable” model is fundamentally at odds with higher-level functional programming. Reachability types offer an alternative: they enable safe sharing and escape of mutable data by tracking which resources each expression can reach. To track internal reachability within complex object graphs, reachability types adopt self-references that let components refer to enclosing resources from inside, just like this pointers in OO languages. While natural for declaratively typing escaping data, self-references complicate subtyping and furthermore type inference: variance restricts where self-references may appear, yet useful type conversions must allow them to vary in controlled ways, which in turn imposes constraints on inference. As an undesirable result, prior works require programmers to insert term-level coercions for even just avoidance —avoiding ill-scoped names in types. With all prior works being declarative, we investigate algorithmic reachability types in this work. We introduce a refined subtyping relation that permits more flexible usages of self-references. We further develop a sound and decidable bidirectional typing algorithm, implemented and verified in Lean. The algorithm automatically avoids ill-scoped names in types, and infers qualifiers via a lightweight unification mechanism. As a step towards practical reachability programming, we show that the system is capable of tracking diverse reachability patterns without explicit coercions in complex Church-encoded datatypes.

Local reasoning about programs that combine aliasing and mutable state is a longstanding challenge. Existing approaches – ownership systems, linear and affine types, uniqueness types, and lexical effect tracking – impose global restrictions such as uniqueness or linearity, or rely on shallow syntactic analyses. These designs fall short with higher-order functions and shared mutable state. Reachability Types (RT) track aliasing and separation in higher-order programs, ensuring runtime safety and non-interference. However, RT systems face three key limitations: (1) they prohibit cyclic references, ruling out non-terminating computations and fixed-point combinators; (2) they require deep tracking, where a qualifier must include all transitively reachable locations, reducing precision and hindering optimizations like fine-grained parallelism; and (3) referent qualifier invariance prevents referents from escaping their allocation contexts, making reference factories inexpressible. In this work, we address these limitations by extending RT with three mechanisms that enhance expressiveness. First, we introduce cyclic references, enabling recursive patterns to be encoded directly through the store. Second, we adopt shallow qualifier tracking, decoupling references from their transitively reachable values. Finally, we introduce an escaping rule with reference subtyping, allowing referent qualifiers to outlive their allocation context. These extensions are formalized in the F < : ∘ -calculus with a mechanized proof of type soundness, and case studies illustrate expressiveness through fixpoint combinators, non-interfering parallelism, and escaping read-only references.

Reachability types are a recent proposal to bring Rust-style reasoning about memory properties to higher-level languages, with a focus on higher-order functions, parametric types, and shared mutable state - features that are only partially supported by current techniques as employed in Rust. While prior work has established key type soundness results for reachability types using the usual syntactic techniques of progress and preservation, stronger metatheoretic properties have so far been unexplored. This paper presents an alternative semantic model of reachability types using logical relations, providing a framework in which we study key properties of interest: (1) semantic type soundness, including of not syntactically well-typed code fragments, (2) termination, especially in the presence of higher-order mutable references, (3) effect safety, especially the absence of observable mutation, and, finally, (4) program equivalence, especially reordering of non-interfering expressions for parallelization or compiler optimization.

Fueled by the success of Rust, many programming languages are adding substructural features to their type systems. The promise of tracking properties such as lifetimes and sharing is tremendous, not just for low-level memory management, but also for controlling higher-level resources and capabilities. But so are the difficulties in adapting successful techniques from Rust to higher-level languages, where they need to interact with other advanced features, especially various flavors of functional and type-level abstraction. What would it take to bring full-fidelity reasoning about lifetimes and sharing to mainstream languages? Reachability types are a recent proposal that has shown promise in scaling to higher-order but monomorphic settings, tracking aliasing and separation on top of a substrate inspired by separation logic. However, naive extensions on top of the prior reachability type system λ * with type polymorphism and/or precise reachability polymorphism are unsound, making λ * unsuitable for adoption in real languages. Combining reachability and type polymorphism that is precise, sound, and parametric remains an open challenge. This paper presents a rethinking of the design of reachability tracking and proposes new polymorphic reachability type systems. We introduce a new freshness qualifier to indicate variables whose reachability sets may grow during evaluation steps. The new system tracks variables reachable in a single step and computes transitive closures only when necessary, thus preserving chains of reachability over known variables that can be refined using substitution. These ideas yield the simply-typed λ ◆ -calculus with precise lightweight, i.e. , quantifier-free, reachability polymorphism, and the F < : ◆ -calculus with bounded parametric polymorphism over types and reachability qualifiers, paving the way for making true tracking of lifetimes and sharing practical for mainstream languages. We prove type soundness and the preservation of separation property in Coq. We discuss various applications ( e.g. , safe capability programming), possible effect system extensions, and compare our system with Scala’s capture types.

Symbolic execution is a powerful program analysis and testing technique. Symbolic execution engines are usually implemented as interpreters, and the induced interpretation over-head can dramatically inhibit performance. Alternatively, implementation choices based on instrumentation provide a limited ability to transform programs. However, the use of compilation and code generation techniques beyond simple instrumentation remains underexplored for engine construction, leaving potential performance gains untapped. In this paper, we show how to tap some of these gains using sophisticated compilation techniques: We present Gensym, an optimizing symbolic-execution compiler that generates symbolic code which explores paths and generates tests in parallel. The key insight of GensYmis to compile symbolic execution tasks into cooperative concurrency via continuation-passing style, which further enables efficient parallelism. The design and implementation of Gensym is based on partial evaluation and generative programming techniques, which make it high-level and performant at the same time. We compare the performance of Gensym against the prior symbolic-execution compiler LLSC and the state-of-the-art symbolic interpreter KLEE. The results show an average 4.6× speedup for sequential execution and 9.4× speedup for parallel execution on 20 benchmark programs.

Graph-based intermediate representations (IRs) are widely used for powerful compiler optimizations, either interprocedurally in pure functional languages, or intraprocedurally in imperative languages. Yet so far, no suitable graph IR exists for aggressive global optimizations in languages with both effects and higher-order functions: aliasing and indirect control transfers make it difficult to maintain sufficiently granular dependency information for optimizations to be effective. To close this long-standing gap, we propose a novel typed graph IR combining a notion of reachability types with an expressive effect system to compute precise and granular effect dependencies at an affordable cost while supporting local reasoning and separate compilation. Our high-level graph IR imposes lexical structure to represent structured control flow and nesting, enabling aggressive and yet inexpensive code motion and other optimizations for impure higher-order programs. We formalize the new graph IR based on a λ-calculus with a reachability type-and-effect system along with a specification of various optimizations. We present performance case studies for tensor loop fusion, CUDA kernel fusion, symbolic execution of LLVM IR, and SQL query compilation in the Scala LMS compiler framework using the new graph IR. We observe significant speedups of up to 21 x .

Protecting confidential data against memory disclosure attacks is crucial to many critical applications, especially those involve cryptographic operations. However, it is neither easy to identify involved cryptographic confidential data in a program nor to implement a fine-grained and yet efficient protection. Existing defensive techniques face many shortcomings such as coarse-grained protection or exorbitant overhead. As a result, real world crypto applications seldom applied this kind of protection in practice.To make the protection of cryptographic confidential data practical, we design and implement CRYPTOMPK, a source code analysis and transformation system to implement a domain-based memory isolation. CRYPTOMPK first automatically tracks and labels all sensitive memory buffers and operations in source code with a context-sensitive, crypto-aware information flow analysis. Then it partitions the source code into crypto and non-crypto domains with a context-dependent privilege switch instrumentation. By further utilizing Intel Memory Protection Keys (MPK), CRYPTOMPK generates executables with efficient domain switching, protecting them against typical memory disclosure vulnerabilities such as arbitrary memory read. In particular, by using CRYPTOMPK, a large number of intermediate memory buffers that have been previously ignored before are well protected, and thus the security risks are reduced significantly. We leveraged CRYPTOMPK to protect prevalent applications such as Apache and Nginx with widely used crypto libraries (e.g., OpenSSL, LibSodium). CRYPTOMPK only needs several minutes to analyze each of these complex cryptographic programs and incurs at most 9.53% performance overhead for the protected programs.

Phase noise caused by the unideal local oscillators limits the self-interference cancellation performance severely in full-duplex systems. In this paper, a novel digital polarization self-interference cancellation method is proposed to break the bottleneck of phase noise. The basic idea here is that the polarization is insensitive to the absolute phase and will not be affected by the random phase noise. Without any prior knowledge of the phase noise, the proposed method exploits the polarization signal processing to transform the multiplicative phase noise to a new additive white Gaussian noise, which benefits from the vectorial property of polarization. Based on the polarization system and signal models with the phase noises both in the upconversion and the downconversion, we demonstrate that the self-interference can be cancelled by regeneration where only a transformed additive white Gaussian noise exists. Moreover, the proposed method obtains an upper bound for digital self-interference cancellation when the phase noise exists if the dual-polarized channel estimation is perfect. The simulation is conducted in advanced design system, and results show that the proposed method cancels the self-interference to noise floor.

The cloudbow structure is directly related to the retrieval of cloud droplet size distribution (droplet effective radius and effective variance). This study investigated the effect of the cloud optical thickness, ground surface albedo and the above-cloud absorbing dust layer on the cloudbow structure based on the modeled airborne directional polarimetric camera (DPC) measurements, which are simulated in 670 nm using Mie scattering theory and the vector radiative transfer mode. It is found that the polarized reflectance increase as the increase of the cloud optical thickness (COT) and saturate when COT=10. The absorbing dust layer's signal would cover the signal from the cloud layer as the aerosol optical thickness increased to 1. Additionally, the surface albedo has negligible effect on the cloudbow structure.