Static Type Research Articles

On the reaction to deprecation of clients of 4 + 1 popular Java APIs and the JDK

Application Programming Interfaces (APIs) are a tremendous resource—that is, when they are stable. Several studies have shown that this is unfortunately not the case. Of those, a large-scale study of API changes in the Pharo Smalltalk ecosystem documented several findings about API deprecations and their impact on API clients. We extend this study, by analyzing clients of both popular third-party Java APIs and the JDK API. This results in a dataset consisting of more than 25,000 clients of five popular Java APIs on GitHub, and 60 clients of the JDK API from Maven Central. This work addresses several shortcomings of the previous study, namely: a study of several distinct API clients in a popular, statically-typed language, with more accurate version information. We compare and contrast our findings with the previous study and highlight new ones, particularly on the API client update practices and the startling similarities between reaction behavior in Smalltalk and Java. We make a comparison between reaction behavior for third-party APIs and JDK APIs, given that language APIs are a peculiar case in terms of wide-spread usage, documentation, and support from IDEs. Furthermore, we investigate the connection between reaction patterns of a client and the deprecation policy adopted by the API used.

The VM already knew that: leveraging compile-time knowledge to optimize gradual typing

Programmers in dynamic languages wishing to constrain and understand the behavior of their programs may turn to gradually-typed languages, which allow types to be specified optionally and check values at the boundary between dynamic and static code. Unfortunately, the performance cost of these run-time checks can be severe, slowing down execution by at least 10x when checks are present. Modern virtual machines (VMs) for dynamic languages use speculative techniques to improve performance: If a particular value was seen once, it is likely that similar values will be seen in the future. They combine optimization-relevant properties of values into cacheable “shapes”, then use a single shape check to subsume checks for each property. Values with the same memory layout or the same field types have the same shape. This greatly reduces the amount of type checking that needs to be performed at run-time to execute dynamic code. While very valuable to the VM’s optimization, these checks do little to benefit the programmer aside from improving performance. We present in this paper a design for intrinsic object contracts, which makes the obligations of gradually-typed languages’ type checks an intrinsic part of object shapes, and thus can subsume run-time type checks into existing shape checks, eliminating redundant checks entirely. With an implementation on a VM for JavaScript used as a target for SafeTypeScript’s soundness guarantees, we demonstrate slowdown averaging 7% in fully-typed code relative to unchecked code, and no more than 45% in pessimal configurations.

Type test scripts for TypeScript testing

TypeScript applications often use untyped JavaScript libraries. To support static type checking of such applications, the typed APIs of the libraries are expressed as separate declaration files. This raises the challenge of checking that the declaration files are correct with respect to the library implementations. Previous work has shown that mismatches are frequent and cause TypeScript's type checker to misguide the programmers by rejecting correct applications and accepting incorrect ones. This paper shows how feedback-directed random testing, which is an automated testing technique that has mostly been used for testing Java libraries, can be adapted to effectively detect such type mismatches. Given a JavaScript library with a TypeScript declaration file, our tool TSTEST generates a "type test script", which is an application that interacts with the library and tests that it behaves according to the type declarations. Compared to alternative solutions that involve static analysis, this approach finds significantly more mismatches in a large collection of real-world JavaScript libraries with TypeScript declaration files, and with fewer false positives. It also has the advantage that reported mismatches are easily reproducible with concrete executions, which aids diagnosis and debugging.

The LISP 2 Project

John McCarthy designed the LISP programming language for the symbolic computation typical of artificial intelligence at the time, and LISP was strongly associated with AI at least through the 1990s. By 1963, a number of ideas had been proposed for how LISP 1.5 could be improved and extended. This lead to the LISP 2 project, which was carried out at System Development Corporation by personnel from SDC and Information International, Inc., using the military AN/FSQ-32 computer. LISP 2 extended LISP 1.5 with ALGOL-like syntax, static type checking, efficient support for arithmetic and arrays, pattern-matching, and more, but the LISP 2 language failed to displace LISP 1.5. Despite this, LISP 2 foreshadowed later languages, such as ECL, Common Lisp, and Java. An online archive of LISP 2 documents and source code exists at the Computer History Museum, providing a snapshot of mid-1960s ARPA-funded research and development.

A large-scale study of programming languages and code quality in GitHub

What is the effect of programming languages on software quality? This question has been a topic of much debate for a very long time. In this study, we gather a very large data set from GitHub (728 projects, 63 million SLOC, 29,000 authors, 1.5 million commits, in 17 languages) in an attempt to shed some empirical light on this question. This reasonably large sample size allows us to use a mixed-methods approach, combining multiple regression modeling with visualization and text analytics, to study the effect of language features such as static versus dynamic typing and allowing versus disallowing type confusion on software quality. By triangulating findings from different methods, and controlling for confounding effects such as team size, project size, and project history, we report that language design does have a significant, but modest effect on software quality. Most notably, it does appear that disallowing type confusion is modestly better than allowing it, and among functional languages, static typing is also somewhat better than dynamic typing. We also find that functional languages are somewhat better than procedural languages. It is worth noting that these modest effects arising from language design are overwhelmingly dominated by the process factors such as project size, team size, and commit size. However, we caution the reader that even these modest effects might quite possibly be due to other, intangible process factors, for example, the preference of certain personality types for functional, static languages that disallow type confusion.

Structural Resolution for Abstract Compilation of Object-Oriented Languages

We propose abstract compilation for precise static type analysis of object-oriented languages based on coinductive logic programming. Source code is translated to a logic program, then type-checking and inference problems amount to queries to be solved with respect to the resulting logic program. We exploit a coinductive semantics to deal with infinite terms and proofs produced by recursive types and methods. Thanks to the recent notion of structural resolution for coinductive logic programming, we are able to infer very precise type information, including a class of irrational recursive types causing non-termination for previously considered coinductive semantics. We also show how to transform logic programs to make them satisfy the preconditions for the operational semantics of structural resolution, and we prove this step does not affect the semantics of the logic program.

Study on The Relationship Between the Structural Design and Shell Fabric of Men's Trousers Based on Skin Stretch

In general, for the majority of men, the amount of exercise is relatively large, so the dress requirements for the men's trousers gradually have new requirements. It pays more attention to comfort and personality. The theoretical basis of the clothing loose amount and structural design are both the shape change caused by skin stretch of human body under various movement conditions, the human body has different postures, which will generate different skin stretch data. The combination of static body type and dynamic movements of human body determines clothing structure design, different body movements, different degree of movements and changes in skin stretch all have a direct impact on the form of clothing attached to the human body.

Rapid Frequency Response From Smart Loads in Great Britain Power System

Flexibility in certain types of loads could be exploited to provide fast and controllable power reserve if the supply voltage/frequency is controlled using existing power electronic interfaces (e.g., motor drives) or additional ones like recently proposed electric springs. Such a load together with its power electronic interface forms a so called smart load. Effectiveness of static smart loads for primary frequency response provision has been shown in the previous papers through case studies on a segment of the low voltage/medium voltage (LV/MV) distribution network. In this paper, collective contribution of both static and motor type smart loads to rapid frequency response provision is demonstrated through a case study on the Great Britain (GB) transmission system. The active power reserve available from such smart loads are quantified and aggregated at each node at the transmission level (275/400 kV). The study shows that the smart loads collectively offer a short-term power reserve which is comparable to the spinning reserve in the GB system, and thus can ensure acceptable frequency deviation and its rate of change following a large infeed loss.

Static Analysis of Model Transformations

Model transformations are central to Model-Driven Engineering (MDE), where they are used to transform models between different languages; to refactor and simulate models; or to generate code from models. Thus, given their prominent role in MDE, practical methods helping in detecting errors in transformations and automate their verification are needed. In this paper, we present a method for the static analysis of ATL model transformations. The method aims at discovering typing and rule errors, like unresolved bindings, uninitialized features or rule conflicts. It relies on static analysis and type inference, and uses constraint solving to assert whether a source model triggering the execution of a given problematic statement can possibly exist. Our method is supported by a tool that integrates seamlessly with the ATL development environment. To evaluate the usefulness of our method, we have used it to analyse a public repository of ATL transformations. The high number of errors discovered shows that static analysis of ATL transformations is needed in practice. Moreover, we have measured the precision and recall of the method by considering a synthetic set of transformations obtained by mutation techniques, and comparing with random testing. The experiment shows good overall results in terms of false positives and negatives.

On polymorphic gradual typing

We study an extension of gradual typing—a method to integrate dynamic typing and static typing smoothly in a single language—to parametric polymorphism and its theoretical properties, including conservativity of typing and semantics over both statically and dynamically typed languages, type safety, blame-subtyping theorem, and the gradual guarantee—the so-called refined criteria, advocated by Siek et al. We develop System F G , which is a gradually typed extension of System F with the dynamic type and a new type consistency relation, and translation to a new polymorphic blame calculus System F C , which is based on previous polymorphic blame calculi by Ahmed et al. The design of System F G and System F C , geared to the criteria, is influenced by the distinction between static and gradual type variables, first observed by Garcia and Cimini. This distinction is also useful to execute statically typed code without incurring additional overhead to manage type names as in the prior calculi. We prove that System F G satisfies most of the criteria: all but the hardest property of the gradual guarantee on semantics. We show that a key conjecture to prove the gradual guarantee leads to the Jack-of-All-Trades property, conjectured as an important property of the polymorphic blame calculus by Ahmed et al.

Effect-driven QuickChecking of compilers

How does one test a language implementation with QuickCheck (aka. property-based testing)? One approach is to generate programs following the grammar of the language. But in a statically-typed language such as OCaml too many of these candidate programs will be rejected as ill-typed by the type checker. As a refinement Pałka et al. propose to generate programs in a goal-directed, bottom-up reading up of the typing relation. We have written such a generator. However many of the generated programs has output that depend on the evaluation order, which is commonly under-specified in languages such as OCaml, Scheme, C, C++, etc. In this paper we develop a type and effect system for conservatively detecting evaluation-order dependence and propose its goal-directed reading as a generator of programs that are independent of evaluation order. We illustrate the approach by generating programs to test OCaml's two compiler backends against each other and report on a number of bugs we have found doing so.

Gradual session types

Session types are a rich type discipline, based on linear types, that lift the sort of safety claims that come with type systems to communications. However, web-based applications and micro services are often written in a mix of languages, with type disciplines in a spectrum between static and dynamic typing. Gradual session types address this mixed setting by providing a framework which grants seamless transition between statically typed handling of sessions and any required degree of dynamic typing. We propose GradualGV as an extension of the functional session type system GV with dynamic types and casts. We demonstrate type and communication safety as well as blame safety, thus extending previous results to functional languages with session-based communication. The interplay of linearity and dynamic types requires a novel approach to specifying the dynamics of the language.

Chaperone contracts for higher-order sessions

Contracts have proved to be an effective mechanism that helps developers in identifying those modules of a program that violate the contracts of the functions and objects they use. In recent years, sessions have established as a key mechanism for realizing inter-module communications in concurrent programs. Just like values flow into or out of a function or object, messages are sent on, and received from, a session endpoint. Unlike conventional functions and objects, however, the kind, direction, and properties of messages exchanged in a session may vary over time, as the session progresses. This feature of sessions calls for contracts that evolve along with the session they describe. In this work, we extend to sessions the notion of chaperone contract (roughly, a contract that applies to a mutable object) and investigate the ramifications of contract monitoring in a higher-order language that features sessions. We give a characterization of correct module, one that honors the contracts of the sessions it uses, and prove a blame theorem. Guided by the calculus, we describe a lightweight implementation of monitored sessions as an OCaml module with which programmers can benefit from static session type checking and dynamic contract monitoring using an off-the-shelf version of OCaml.

A framework for adaptive differential privacy

Differential privacy is a widely studied theory for analyzing sensitive data with a strong privacy guarantee—any change in an individual's data can have only a small statistical effect on the result—and a growing number of programming languages now support differentially private data analysis. A common shortcoming of these languages is poor support for adaptivity . In practice, a data analyst rarely wants to run just one function over a sensitive database, nor even a predetermined sequence of functions with fixed privacy parameters; rather, she wants to engage in an interaction where, at each step, both the choice of the next function and its privacy parameters are informed by the results of prior functions. Existing languages support this scenario using a simple composition theorem , which often gives rather loose bounds on the actual privacy cost of composite functions, substantially reducing how much computation can be performed within a given privacy budget. The theory of differential privacy includes other theorems with much better bounds, but these have not yet been incorporated into programming languages. We propose a novel framework for adaptive composition that is elegant, practical, and implementable. It consists of a reformulation based on typed functional programming of privacy filters , together with a concrete realization of this framework in the design and implementation of a new language, called Adaptive Fuzz . Adaptive Fuzz transplants the core static type system of Fuzz to the adaptive setting by wrapping the Fuzz typechecker and runtime system in an outer adaptive layer , allowing Fuzz programs to be conveniently constructed and typechecked on the fly. We describe an interpreter for Adaptive Fuzz and report results from two case studies demonstrating its effectiveness for implementing common statistical algorithms over real data sets.

Theorems for free for free: parametricity, with and without types

The polymorphic blame calculus integrates static typing, including universal types, with dynamic typing. The primary challenge with this integration is preserving parametricity: even dynamically-typed code should satisfy it once it has been cast to a universal type. Ahmed et al. (2011) employ runtime type generation in the polymorphic blame calculus to preserve parametricity, but a proof that it does so has been elusive. Matthews and Ahmed (2008) gave a proof of parametricity for a closely related system that combines ML and Scheme, but later found a flaw in their proof. In this paper we present an improved version of the polymorphic blame calculus and we prove that it satisfies relational parametricity. The proof relies on a step-indexed Kripke logical relation. The step-indexing is required to make the logical relation well-defined in the case for the dynamic type. The possible worlds include the mapping of generated type names to their types and the mapping of type names to relations. We prove the Fundamental Property of this logical relation and that it is sound with respect to contextual equivalence. To demonstrate the utility of parametricity in the polymorphic blame calculus, we derive two free theorems.

Remark on theEPPin Labeling Theory: Evidence from Romance

AbstractThis paper puts forward an account of the Extended Projection Principle (EPP) based on Chomsky's (2013, 2015) Labeling Theory. Departing from Chomsky's (2015) proposal, which adopts “feature strength” (Chomsky 1993, 1995), it is suggested that the need for Spec,TPto be occupied by aDPcan be attributed to labeling reasons, under the assumption that T is a copy of C (these heads being “bundled” in the lexicon of languages of the English type). Given that copies are inert for computational operations (Chomsky 2000, 2001), it follows that they fail to label (Chomsky 2013), which in turn makes it mandatory for Spec,TPto be filled. This article explores the consequences of this proposal for null‐subject languages, in which C and T are regarded as independent lexical items.

Functional BIP: Embedding connectors in functional programming languages

This paper presents a theoretical foundation for functional language implementations of Behaviour–Interaction–Priority (BIP). We introduce a set of connector combinators describing synchronisation, data transfer, priorities and dynamicity in a principled way. A static type system ensures the soundness of connector semantics.Based on this foundation, we implemented BIP as an embedded domain specific language (DSL) in Haskell and Scala. The DSL embedding allows programmers to benefit from the full expressive power of high-level languages. The clear separation of behaviour and coordination inherited from BIP leads to systems that are arguably simpler to maintain and reason about, compared to other approaches.

Преподавание русского языка в новом типе образовательной среды российского вуза

Преподавание русского языка в новом типе образовательной среды российского вуза

On the Quantized Dynamics of Factorial Languages

We study local piecewise conjugacy of the quantized dynamics arising from factorial languages. We show that it induces a bijection between allowable words of same length and thus it preserves entropy. In the case of sofic factorial languages we prove that local piecewise conjugacy translates to unlabeled graph isomorphism of the follower set graphs. Moreover it induces an unlabeled graph isomorphism between the Fischer covers of irreducible subshifts. We verify that local piecewise conjugacy does not preserve finite type nor irreducibility; but it preserves soficity. Moreover it implies identification (up to a permutation) for factorial languages of type $1$ if, and only if, the follower set function is one-to-one on the symbol set.

A toroidal‐lens designed structure for static type table‐top floating image system with horizontal parallax function

AbstractA new structure of horizontal parallax table‐top floating image system with toroidal‐lens optical film was developed. In this design, the circular arranged pico‐projectors limit the angular resolution of this system and display the floating image for surrounding viewing zones. In addition, the pinhole array and toroidal‐lens layer compose the optical film in the system and correspond with each other; both of them could be considered as a repeatable unit to control the spatial resolution of image. After passing through the optical film, the direction, position, shape, and divergence angle of light field could be controlled as fan ray, which has a widely scattered angle in latitude and high directivity in longitude direction. Moreover, to confirm the optical properties, the proposed structure was built in the commercially optical software, LightTools v8.3, which is widely used in the simulation of light distribution. Based on the imaging principle and the inverse light tracking method, displaying floating image with circular viewing zones would be achieved.