Imperative Programming Research Articles

Software synthesis procedures

Automated synthesis of program fragments from specifications can make programs easier to write and easier to reason about. To integrate synthesis into programming languages, software synthesis algorithms should behave in a predictable way: they should succeed for a well-defined class of specifications. We propose to systematically generalize decision procedures into synthesis procedures , and use them to compile implicitly specified computations embedded inside functional and imperative programs. Synthesis procedures are predictable, because they are guaranteed to find code that satisfies the specification whenever such code exists. To illustrate our method, we derive synthesis procedures by extending quantifier elimination algorithms for integer arithmetic and set data structures. We then show that an implementation of such synthesis procedures can extend a compiler to support implicit value definitions and advanced pattern matching.

Constraints as control

We present an extension of Scala that supports constraint programming over bounded and unbounded domains. The resulting language, Kaplan, provides the benefits of constraint programming while preserving the existing features of Scala. Kaplan integrates constraint and imperative programming by using constraints as an advanced control structure; the developers use the monadic 'for' construct to iterate over the solutions of constraints or branch on the existence of a solution. The constructs we introduce have simple semantics that can be understood as explicit enumeration of values, but are implemented more efficiently using symbolic reasoning. Kaplan programs can manipulate constraints at run-time, with the combined benefits of type-safe syntax trees and first-class functions. The language of constraints is a functional subset of Scala, supporting arbitrary recursive function definitions over algebraic data types, sets, maps, and integers. Our implementation runs on a platform combining a constraint solver with a standard virtual machine. For constraint solving we use an algorithm that handles recursive function definitions through fair function unrolling and builds upon the state-of-the art SMT solver Z3. We evaluate Kaplan on examples ranging from enumeration of data structures to execution of declarative specifications. We found Kaplan promising because it is expressive, supporting a range of problem domains, while enabling full-speed execution of programs that do not rely on constraint programming.

Recursive proofs for inductive tree data-structures

We develop logical mechanisms and procedures to facilitate the verification of full functional properties of inductive tree data-structures using recursion that are sound, incomplete, but terminating. Our contribution rests in a new extension of first-order logic with recursive definitions called Dryad, a syntactical restriction on pre- and post-conditions of recursive imperative programs using Dryad, and a systematic methodology for accurately unfolding the footprint on the heap uncovered by the program that leads to finding simple recursive proofs using formula abstraction and calls to SMT solvers. We evaluate our methodology empirically and show that several complex tree data-structure algorithms can be checked against full functional specifications automatically, given pre- and post-conditions. This results in the first automatic terminating methodology for proving a wide variety of annotated algorithms on tree data-structures correct, including max-heaps, treaps, red-black trees, AVL trees, binomial heaps, and B-trees.

Унификация программ

To unify a pair of algebraic expressions t1 and t2 is to find out such a substitution θ that both terms t1θ and t2θ have the same meaning. Unification problem can be extended to computational programs. To unify a pair of programs π1 and π2 is to build two sequences of assignment statements ρ1 : x1 := t1; x2 := t2; … xn := tn and ρ1 : y1 := s1; y2 := s2; … ym := sm, such that both compositions of programs ρ1;π1 and ρ2;π2 are equivalent (i.e. they compute the same function). In this paper we deal with logic-and-term equivalence introduced in 1972 by V. Itkin. This is the most weak decidable equivalence on programs that approximates the functional equivalence. Based on the polynomial-time equivalence checking algorithm for logic-and-term equivalence in the firstorder model of imperative programs we introduce a polynomial-time unification algorithm which computes the most general unifier (ρ1, ρ2) for every pair of sequential imperative (π1, π2) w.r.t. logic-and-term equivalence. After discussing the importance of unification proble for program refactoring and optimization we briefly recall the basic concepts of term substitution theory and theory of program schemata. Then we introduce a formal model of sequential programs we deal with, and finally we present our unification algorithm, prove its correctness and show that its complexity is polynomial on the size of programs to be unified.

Discovering invariants via simple component analysis

We propose a new technique combining dynamic and static analysis of programs to find linear invariants. We use a statistical tool, called simple component analysis, to analyze partial execution traces of a given program. We get a new coordinate system in the vector space of program variables, which is used to specialize numerical abstract domains. As an application, we instantiate our technique to interval analysis of simple imperative programs and show some experimental evaluations.

A symbolic analysis framework for static analysis of imperative programming languages

We present a generic symbolic analysis framework for imperative programming languages. Our framework is capable of computing all valid variable bindings of a program at given program points. This information is invaluable for domain-specific static program analyses such as memory leak detection, program parallelization, and the detection of superfluous bound checks, variable aliases and task deadlocks.We employ path expression algebra to model the control flow information of programs. A homomorphism maps path expressions into the symbolic domain. At the center of the symbolic domain is a compact algebraic structure called supercontext. A supercontext contains the complete control and data flow analysis information valid at a given program point.Our approach to compute supercontexts is based purely on algebra and is fully automated. This novel representation of program semantics closes the gap between program analysis and computer algebra systems, which makes supercontexts an ideal symbolic intermediate representation for all domain-specific static program analyses.Our approach is more general than existing methods because it can derive solutions for arbitrary (even intra-loop and nested loop) nodes of reducible and irreducible control flow graphs. We prove the correctness of our symbolic analysis method. Our experimental results show that the problem sizes arising from real-world applications such as the SPEC95 benchmark suite are tractable for our symbolic analysis framework.

C program verification in SPECTRUM multilanguage system

An extendable multilanguage analysis and verification system SPECTRUM is presented; this system is being developed in the framework of the project SPECTRUM. The prospects of the application of this system are demonstrated, as exemplified by the verification of C programs. The project SPECTRUM is aimed at the creation of a new integrated approach to the verification of imperative programs that makes it possible to integrate, unify, and combine methods and approaches for verification of imperative programs and accumulate and apply information about these programs. The specific feature of this approach is the application of a specialized executable specification language Atoment for the development of program verification tools; this language makes it possible to represent methods and approaches for verification and data for them (program models, annotations, logical formulae) in a unified format. The C component of the SPECTRUM system uses a two-level C program verification method. This method is a good illustration of the integrated approach, since it provides complex verification of C programs based on a combination of the operational, axiomatic, and transformational approaches.

Reactive imperative programming with dataflow constraints

Dataflow languages provide natural support for specifying constraints between objects in dynamic applications, where programs need to react efficiently to changes of their environment. Researchers have long investigated how to take advantage of dataflow constraints by embedding them into procedural languages. Previous mixed imperative/dataflow systems, however, require syntactic extensions or libraries of ad hoc data types for binding the imperative program to the dataflow solver. In this paper we propose a novel approach that smoothly combines the two paradigms without placing undue burden on the programmer. In our framework, programmers can define ordinary statements of the imperative host language that enforce constraints between objects stored in special memory locations designated as "reactive". Differently from previous approaches, reactive objects can be of any legal type in the host language, including primitive data types, pointers, arrays, and structures. Statements defining constraints are automatically re-executed every time their input memory locations change, letting a program behave like a spreadsheet where the values of some variables depend upon the values of other variables. The constraint solving mechanism is handled transparently by altering the semantics of elementary operations of the host language for reading and modifying objects. We provide a formal semantics and describe a concrete embodiment of our technique into C/C++, showing how to implement it efficiently in conventional platforms using off-the-shelf compilers. We discuss common coding idioms and relevant applications to reactive scenarios, including incremental computation, observer design pattern, and data structure repair. The performance of our implementation is compared to ad hoc problem-specific change propagation algorithms, as well as to language-centric approaches such as self-adjusting computation and subject/observer communication mechanisms, showing that the proposed approach is efficient in practice.

Backstage Java

We propose Backstage Java (BSJ), a Java language extension which allows algorithmic, contextually-aware generation and transformation of code. BSJ explicitly and concisely represents design patterns and other encodings by employing compile-time metaprogramming: a practice in which the programmer writes instructions which are executed over the program's AST during compilation. While compile-time metaprogramming has been successfully used in functional languages such as Template Haskell, a number of language properties (scope, syntactic structure, mutation, etc.) have thus far prevented this theory from translating to the imperative world. BSJ uses the novel approach of difference-based metaprogramming to provide an imperative programming style amenable to the Java community and to enforce that metaprograms are consistent and semantically unambiguous. To make the feasibility of BSJ metaprogramming evident, we have developed a compiler implementation and numerous working code examples.

Assessment Training in Principal Preperation Programs

The role of the administrator has evolved over the past 30 years from manager to instructional leader. As instructional leaders, administrators are now responsible for student achievement on high-stakes state-mandated assessments. Therefore, it is imperative principal preparation programs provide the necessary training instructional leaders need to analyze and interpret assessment data and make informed decisions toward school improvement. This descriptive study analyzes four syllabi components to determine the extent to which testing and measurement are covered in each course: objectives, classroom sessions, resources, and activities. Based on responses from 30 universities across the United States, less than 30% of principal preparation programs are preparing candidates to be data-driven decision-makers. The most frequently adopted textbooks provided practical applications, and respondents used a wide variety of activities that provided relevant data-driven experiences; however, less than 50% of respondents spent at least 19 hours on testing and measurement in a 45-hour semester. The researchers make recommendations principal preparation programs may include to increase data-driven decision-making experiences. Keywords: principal preparation, data-driven decisions, assessment, school leaders

Project and Implementation for a Programming Language Suitable to Express Adaptive Algorithms

This article describes a implementation propose for a high level programming language suitable to express adaptive algorithms following the programming languages proposed in [1] and the programming paradigm described in [2]. Instead specify a new programming language, the Oberon programming language [5] was choose and added to it a special syntax to express adaptive algorithms united with the usual imperative programming. To generate machine code was used LLVM [3] (Low Level Virtual Machine), a avaliable library used to study compiler algorithms and able to generate executable code for several computer achitectures. This propose was performed and the results are shown in the attachments section in this article.

Characteristic formulae for the verification of imperative programs

In previous work, we introduced an approach to program verification based on characteristic formulae. The approach consists of generating a higher-order logic formula from the source code of a program. This characteristic formula is constructed in such a way that it gives a sound and complete description of the semantics of that program. The formula can thus be exploited in an interactive proof assistant to formally verify that the program satisfies a particular specification. This previous work was, however, only concerned with purely-functional programs. In the present paper, we describe the generalization of characteristic formulae to an imperative programming language. In this setting, characteristic formulae involve specifications expressed in the style of Separation Logic. They also integrate the frame rule, which enables local reasoning. We have implemented a tool based on characteristic formulae. This tool, called CFML, supports the verification of imperative Caml programs using the Coq proof assistant. Using CFML, we have formally verified nontrivial imperative algorithms, as well as CPS functions, higher-order iterators, and programs involving higher-order stores.

Two-Language, Two-Paradigm Introductory Computing Curriculum Model and its Implementation

This paper analyzes difficulties with the introduction of object-oriented concepts in introductory computing education and then proposes a two-language, two-paradigm curriculum model that alleviates such difficulties. Our two-language, two-paradigm curriculum model begins with teaching imperative programming using Python programming language, continues with teaching object-oriented computing using Java, and concludes with teaching object-oriented data structures with Java.

Compiler design: virtual machines

While compilers for high-level programming languages are large complex software systems, they have particular characteristics that differentiate them from other software systems. Their functionality is almost completely well-defined ideally there exist complete precise descriptions of the source and target languages, while additional descriptions of the interfaces to the operating system, programming system and programming environment, and to other compilers and libraries are often available. The implementation of application systems directly in machine language is both difficult and error-prone, leading to programs that become obsolete as quickly as the computers for which they were developed. With the development of higher-level machine-independent programming languages came the need to offer compilers that were able to translate programs into machine language. Given this basic challenge, the different subtasks of compilation have been the subject of intensive research since the 1950s. This book is not intended to be a cookbook for compilers, instead the authors' presentation reflects the special characteristics of compiler design, especially the existence of precise specifications of the subtasks. They invest effort to understand these precisely and to provide adequate concepts for their systematic treatment. This is the first book in a multivolume set, and here the authors describe what a compiler does, i.e., what correspondence it establishes between a source and a target program. To achieve this the authors specify a suitable virtual machine (abstract machine) and exactly describe the compilation of programs of each source language into the language of the associated virtual machine for an imperative, functional, logic and object-oriented programming language. This book is intended for students of computer science. Knowledge of at least one imperative programming language is assumed, while for the chapters on the translation of functional and logic programming languages it would be helpful to know a modern functional language and Prolog. The book is supported throughout with examples, exercises and program fragments.

Path-based inductive synthesis for program inversion

In this paper, we investigate the problem of semi-automated inversion of imperative programs, which has the potential to make it much easier and less error prone to write programs that naturally pair as inverses, such as insert/delete operations, compressors/decompressors, and so on. Viewing inversion as a subproblem of program synthesis, we propose a novel synthesis technique called Path-based inductive synthesis (PINS) and apply it to inversion. PINS starts from a program P and a template T for its inverse. PINS then iteratively refines the space of template instantiations by exploring paths in the composition of P and T with symbolic execution. PINS uses an SMT solver to intelligently guide the refinement process, based on the paths explored so far. The key idea motivating this approach is the small path-bound hypothesis : that the behavior of a program can be summarized with a small, carefully chosen set of its program paths. We evaluated PINS by using it to invert 14 programs such as compressors (e.g., Lempel-Ziv-Welch), encoders (e.g., UUEncode), and arithmetic operations (e.g., vector rotation). Most of these examples are difficult or impossible to invert using prior techniques, but PINS was able to invert all of them. We also found that a semi-automated technique we developed to mine a template from the program to be inverted worked well. In our experiments, PINS takes between one second to thirty minutes to synthesize inverses. We believe this proof-of-concept implementation demonstrates the viability of the PINS approach to program synthesis.

Structural operational semantics through context-dependent behaviour

We present a new approach to providing a structural operational semantics for imperative programming languages with concurrency and procedures. The approach is novel because we expose the building block operations—variable assignment and condition checking—in the labels on the transitions; these form the context-dependent behaviour of a program. Using this style results in two main advantages over standard formalisms for imperative programming language semantics: firstly, our individual transition rules are more concise, and secondly, we are able to more abstractly and intuitively describe the semantics of procedures, including by-value and by-reference parameters. Standard techniques in the literature tend to result in complex and hard-to-read rules for even simple language constructs when procedures and parameters are dealt with. Our semantics for procedures utilises the context-dependent behaviour in the transition label to handle variable name scoping, and defines the semantics of recursion without requiring additional rules. In contrast with Plotkin’s seminal structural operational semantics paper, we do not use locations to describe some of the more complex language constructs. Novel aspects of the abstract syntax include local states (in contrast to a single global store), which simplifies the reasoning about local variables, and a command for dynamically renaming variables (in contrast to mapping variables to locations), which simplifies the reasoning about the effect of procedures on by-reference parameters.

Using Graph Transformations and Graph Abstractions for Software Verification

In this paper we describe our intended approach for the verification of software written in imperative programming languages. We base our approach on model checking of graph transition systems, where each state is a graph and the transitions are specified by graph transformation rules. We believe that graph transformation is a very suitable technique to model the execution semantics of languages with dynamic memory allocation. Furthermore, such representation allows us to investigate the use of graph abstractions, which can mitigate the combinatorial explosion inherent to model checking. In addition to presenting our planned approach, we reason about its feasibility, and, by providing a brief comparison to other existing methods, we highlight the benefits and drawbacks that are expected.

Compilation modulaire d´un langage synchrone Spécification, simulation, implémentation et vérification d´applications synchrones

In this paper, we study the modular compilation of imperative synchronous programs. We rely on a formal framework well suited to perform compilation and formal validation of systems. In practice, we design and implement a special purpose language (LE) and its execution equational semantics that allows the modular compilation of programs into software and hardware targets (C code, Vhdl code, FPGA synthesis, Verification tools). We show the correctness of this semantics, and we introduce a new algorithm to check program causality with respect to our modular approach. Relying in this formal approach, we defined a toolkit dedicated to the compilation and the verification of reactive applications. MOTS-CLES : langages synchrones, methodes formelles, compilation separee, verification

E‐assessment of Matlab assignments in Moodle: Application to an introductory programming course for engineers

AbstractThis article introduces a novel extension for Moodle supporting the automatic verification of codes written in Matlab. It has been applied when teaching the basics of imperative programming in a course aimed at chemical engineering students. The extension derives from the module CTPracticals, originally developed by the authors to enable the automatic assessment of VHDL assignments in Moodle. Several major changes have been made, mainly in the automatic verification engine, in the core of the system, and in several user interfaces. The module partially frees teachers from the repetitive task of verifying assignments, allowing them to invest more time assisting students and tackling new pedagogical objectives. An anonymous student survey proved that students are satisfied with the system because they find the feedback and the constantly updated view of the status of their assignments helpful. © 2011 Wiley Periodicals, Inc. Comput Appl Eng Educ 21: 728–736, 2013

Difficulties in Learning Inheritance and Polymorphism

This article reports on difficulties related to the concepts of inheritance and polymorphism, expressed by a group of 22 in-service CS teachers with an experience with the procedural paradigm, as they coped with a course on OOP. Our findings are based on the analysis of tests, questionnaires that the teachers completed in the course, as well as on observations made during the course. The article suggests that the difficulties are mostly caused by the learners’ ignorance about a programming model for inheritance and polymorphism. Such a model is presented in the appendix. The article offers a classification of the difficulties into the following four clusters: (1) alternative (partial) models, (2) analogies to the use of inheritance and conversion in day-to-day life or in imperative programming, (3) lack of understanding of hierarchies and their role in inheritance, and (4) difficulties due to approaches to teaching, and their impact on the students understanding, as well as, with difficulties that arose in previous stages of learning OOP and have yet not been resolved.