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My objective is to create an intuitive computer for laypeople who want to go beyond ready-made apps and create programs to control their electronic environment. I submit Loke, a new kind of computer that is a universe of objects and nothing but objects. I call it an object computer. Loke is implemented in Squeak, a variant of Smalltalk, and is an extensible, conceptual model for execution, inspection, and exploration. It was first used to demonstrate how Ellen, a novice, programs a smart alarm clock through a GUI adapted to her competence, needs, and preferences. Informal demonstrations indicated that laypeople immediately grasp the idea of communicating objects that represent real things in their environment. They also wanted to use it for their own purposes. They were creative in identifying personal opportunities for Loke and in sketching out their implementations. Interestingly, expert programmers who attended the demonstration did not see the point of Loke. I have completed the programming of Loke qua conceptual model. The model underpins its potential security and privacy and sustains its object and message models. The Loke qua programming environment is still in its infancy, and its inherent security and privacy properties are still not realized in practice. A future Loke device will be accessible from anywhere and embedded in its own hardware to achieve them. The Loke IDE rests on Data–Context–Interaction (DCI), a new programming paradigm that leads to readable code with a clear architecture. I submit Loke for the pleasure of personal programming. [ABSTRACT FROM AUTHOR]

Concurrency issues are inherently harder to identify and fix than issues in sequential programs, due to aspects like indeterminate order of access to shared resources and thread synchronisation. Live debuggers are often used by developers to gain insights into the behaviour of concurrent programs by exploring the call stacks of threads. Nevertheless, contemporary live debuggers for concurrent programs are usually sequential debuggers augmented with the ability to display different threads in isolation. To these debuggers every thread call stack begins with a designated start routine and the calls that led to the creation of the thread are not visible, as they are part of a different thread. This requires developers to manually link stack traces belonging to related but distinct threads, adding another burden to the already difficult act of debugging concurrent programs. To improve debugging of concurrent programs we address the problem of incomplete call stacks in debuggers through a thread and debugger model that enables live debugging of child threads within the context of their parent threads. The proposed debugger operates on a virtual thread that merges together multiple relevant threads. To better understand the features of debuggers for concurrent programs we present an in-depth discussion of the concurrency related features in current live debuggers. We test the applicability of the proposed model by instantiating it for simple threads, local and remote promises, and a remote object-oriented database. Starting from these use cases we further discuss implementation details ensuring a practical approach. [ABSTRACT FROM AUTHOR]

The software industry has to offer increasingly individualized software for a large number of platforms. In a constantly evolving technical context, the appropriateness and the profitableness of a software has to be ensured earlier, before most of the costs have been incurred and before most of the risks have been taken. Feature-Oriented Model-Driven Development (FOMDD) is a promising paradigm to tackle the issue of developing software variants when multiple platforms are targeted. However, because of its model-driven fundament, FOMDD suffers from limited capabilities regarding model execution and early validation. In this paper, we present CrossFabrik, an approach for the design and the early functional validation of feature-based applications. This approach allows the live debugging and editing of the underlying models during a simulation without being forced to stop and restart a validation process. Such an approach relies on the reflective capability of the development environment. An implementation of our approach within Pharo is also presented. [ABSTRACT FROM AUTHOR]

LOGO has been evolving in incremental steps for 40 years. This has resulted in steady progress but some regions of the space of all programming languages for children cannot be reached without passing through unacceptable intermediate designs. What are the ultimate aims of LOGO? What criteria and aesthetics should be used in determining which areas of the design space are most promising? What would the ideal programming language look like? Would a family of special-purpose languages be more effective than a single language? In looking to the future what can we learn from the history of LOGO? What can we learn from other programming systems for children? Alan Kay is leading a new project entitled, ``Steps toward the Reinvention of Programming''. What are its strengths and weaknesses? We can conceptualise the design alternatives as defining an n-dimensional space. Some dimensions represent major alternatives for syntax, others for dealing with concurrency, others for the underlying computational models, and others for features of the programming environment. The goal of this paper is to spur a discussion of these issues. I will present my personal opinions based upon 30 years of research experience in this field.

Understanding the run-time behavior of software systems can be a challenging activity. Debuggers are an essential category of tools used for this purpose as they give developers direct access to the running systems. Nevertheless, traditional debuggers rely on generic mechanisms to introspect and interact with the running systems, while developers reason about and formulate domain-specific questions using concepts and abstractions from their application domains. This mismatch creates an abstraction gap between the debugging needs and the debugging support leading to an inefficient and error-prone debugging effort, as developers need to recover concrete domain concepts using generic mechanisms. To reduce this gap, and increase the efficiency of the debugging process, we propose a framework for developing domain-specific debuggers, called the Moldable Debugger , that enables debugging at the level of the application domain. The Moldable Debugger is adapted to a domain by creating and combining domain-specific debugging operations with domain-specific debugging views , and adapts itself to a domain by selecting, at run time, appropriate debugging operations and views. To ensure the proposed model has practical applicability (i.e., can be used in practice to build real debuggers), we discuss, from both a performance and usability point of view, three implementation strategies. We further motivate the need for domain-specific debugging, identify a set of key requirements and show how our approach improves debugging by adapting the debugger to several domains. [ABSTRACT FROM AUTHOR]

A proxy object is a surrogate or placeholder that controls access to another target object. Proxy objects are a widely used solution for different scenarios such as remote method invocation, future objects, behavioral reflection, object databases, inter-language communications and bindings, access control, lazy or parallel evaluation, security, among others. Most proxy implementations support proxies for regular objects but are unable to create proxies for objects with an important role in the runtime infrastructure such as classes or methods. Proxies can be complex to install, they can have a significant overhead, they can be limited to certain kind of classes, etc. Moreover, proxy implementations are often not stratified and there is no clear separation between proxies (the objects intercepting messages) and handlers (the objects handling interceptions). In this paper, we present Ghost: a uniform and general-purpose proxy implementation for the Pharo programming language. Ghost provides low memory consuming proxies for regular objects as well as for classes and methods. When a proxy takes the place of a class, it intercepts both the messages received by the class and the lookup of methods for messages received by its instances. Similarly, if a proxy takes the place of a method, then the method execution is intercepted too. [ABSTRACT FROM AUTHOR]

After decades of development in programming languages and programming environments, Smalltalk is still one of few environments that provide advanced features and is used in the industry. However, as Java became prevalent, the ability to call a Java code from Smalltalk became important. A traditional approach to integrate the Java and Smalltalk languages is through low-level communication between separate Java and Smalltalk virtual machines. To our best knowledge there is no other project attempting to execute and integrate the Java language directly in the Smalltalk environment. A direct integration allows for a very tight integration of the languages and their objects within a single environment. Yet integration and language interoperability impose challenging issues related to method naming conventions, method overloading, exception handling and thread-locking mechanisms. In this paper we describe ways to overcome these challenges and to integrate Java into the Smalltalk environment. We focus on a possibility to call a Java code from Smalltalk using standard Smalltalk idioms while the semantics of both languages remains preserved. We present stx:libjava – an implementation of a Java virtual machine within Smalltalk/X – as a validation of our approach. [ABSTRACT FROM AUTHOR]

Version control systems (VCS) have become indispensable software development tools. The version snapshots they store to provide support for change coordination and release management, effectively track the evolution of the versioned software and its development process. Despite this wealth of historical information, it has only been leveraged by tools that are dedicated to a specific task such as empirical validation of software engineering practices or fault prediction. General-purpose tool support for reasoning about the historical information stored in a version control system is limited. This paper provides a comprehensive description of a logic-based, general-purpose history query tool called Absinthe . Absinthe supports querying versioned Smalltalk system using logic queries in which quantified regular path expressions are embedded. These expressions lend themselves to specifying the properties that each individual version in a sequence of successive software versions ought to exhibit. To demonstrate the general-purpose nature of our history query tool, we use it to verify development process constraints, to identify temporal bad smells and to answer questions that developers commonly ask. Finally, we compare a query written in Absinthe to an equivalent one written in Smalltalk. [ABSTRACT FROM AUTHOR]

A modern developer is presented with a continuum of choices of programming languages, ranging from assembly languages and C up to high-level domain-specific languages. It is very rare for a single language to be the best possible choice for everything, and the sweet spot with an optimal trade between ease of development and performance changes depending on the target platform. We present an interoperable framework for allowing code written in C (potentially with inline assembly), Objective-C, Smalltalk, and higher-level domain-specific languages to coexist with very low cognitive or performance overhead. Our implementation shares an underlying object model, in interpreted, JIT-compiled and statically compiled code among all languages, allowing a single object to have methods implemented in any of the supported languages. We also describe several techniques that we have used to improve the performance of late-bound dynamic languages. [ABSTRACT FROM AUTHOR]

Refactoring is a crucial activity in agile software development. As a consequence, automated tools are expected to support refactoring, both for reducing the developer's effort as well as for avoiding errors due to manual changes. In this context, the chosen programming language has a major impact on the level of support that an automated refactoring tool can offer. One important aspect of a programming language concerning the automation of refactoring is the type system. While a static type system, present in languages such as Java, provides information about dependencies in the program, the dynamic type system of the Smalltalk programming language offers little information that can be used by automated refactoring tools. This paper focuses on the challenges in the context of refactoring raised by the dynamic type system of Smalltalk. It highlights the problems caused by the absence of static type information and proposes the use of static code analysis for performing type inference to gather information about the dependencies in the program's source code. It explains the mechanism of the static code analysis using sample code and presents a prototype of an enhanced refactoring tool, which uses the structural information extracted through static code analysis. Empirical samples build the base for evaluating the effectiveness of the approach. [ABSTRACT FROM AUTHOR]

Being able to combine static and dynamic typing within the same language has clear benefits in order to support the evolution of prototypes or scripts into mature robust programs. While being an emblematic dynamic object-oriented language, Smalltalk is lagging behind in this regard. We report on the design, implementation and application of Gradualtalk, a gradually-typed Smalltalk meant to enable incremental typing of existing programs. The main design goal of the type system is to support the features of the Smalltalk language, like metaclasses and blocks, live programming, and to accommodate the programming idioms used in practice. We studied a number of existing projects in order to determine the features to include in the type system. As a result, Gradualtalk is a practical approach to gradual types in Smalltalk, with a novel blend of type system features that accommodate most programming idioms. [ABSTRACT FROM AUTHOR]

Implementing UIs is often a tedious task. To address this, UI Builders have been proposed to support the description of widgets, their location, and their logic. A missing aspect of UI Builders is however the ability to reuse and compose widget logic. In our experience, this leads to a significant amount of duplication in UI code. To address this issue, we built Spec: a UIBuilder for Pharo with a focus on reuse. With Spec, widget properties are defined declaratively and attached to specific classes known as composable classes. A composable class defines its own widget description as well as the model-widget bridge and widget interaction logic. This paper presents Spec, showing how it enables seamless reuse of widgets and how these can be customized. After presenting Spec and its implementation, we discuss how its use in Pharo 2.0 has cut in half the amount of lines of code of six of its tools, mostly through reuse. This shows that Spec meets its goals of allowing reuse and composition of widget logic. [ABSTRACT FROM AUTHOR]

Bootstrapping is a technique commonly known by its usage in language definition by the introduction of a compiler written in the same language it compiles. This process is important to understand and modify the definition of a given language using the same language, taking benefit of the abstractions and expression power it provides. A bootstrap, then, supports the evolution of a language. However, the infrastructure of reflective systems like Smalltalk includes, in addition to a compiler, an environment with several self-references. A reflective system bootstrap should consider all its infrastructural components. In this paper, we propose a definition of bootstrap for object-oriented reflective systems, we describe the architecture and components it should contain and we analyze the challenges it has to overcome. Finally, we present a reference bootstrap process for a reflective system and Hazelnut, its implementation for bootstrapping the Pharo Smalltalk-inspired system. [ABSTRACT FROM AUTHOR]

SUMMARY Because objects need to be stored and reloaded on different environments, serializing object graphs is a very important activity. There is a plethora of serialization frameworks with different requirements and design trade-offs. Most of them are based on recursive parsing of the object graphs, an approach which often is too slow. In addition, most of them prioritize a language-agnostic format instead of speed and language-specific object serialization. For the same reason, such serializers usually do not support features such as class-shape changes, global references or executing pre and post load actions. Looking for speed, some frameworks are partially implemented at Virtual Machine (VM) level, hampering code portability and making them difficult to understand, maintain and extend. In this paper, we present Fuel, a general-purpose object serializer based on these principles: (1) speed, through a compact binary format and a pickling algorithm which invests time in serialization for obtaining the best performance on materialization; (2) good object-oriented design, without special help at VM; and (3) serialize any object, thus have a full-featured language-specific format. We implement and validate this approach in Pharo, where we demonstrate that Fuel is faster than other serializers, even those with special VM support. The extensibility of Fuel made possible to successfully serialize various objects: classes in Newspeak, debugger stacks, and full content management system object graphs. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]