Cellular automata are simulations of cells interacting with each other based on simple rules. Despite the simplicity, they can exhibit complex behaviour, and have a number of applications in fields such as medicine, biology, mathematics, and more. As a result, people from a variety of different backgrounds and skill-sets may find cellular automata useful to their work or research. There exist tools to explore well-known automata, but many require some form of textual programming ability, or do not offer easy and approachable ways to customise automata. Our software aims to be more accessible for those without backgrounds in programming or cellular automata, to allow users to more easily explore and modify automata. To achieve this, we have developed a visual programming language, where users can connect components to create their own automata from scratch, without any textual programming.

Package management is instrumental for programming languages and operating systems, and yet it is neglected by both areas as an implementation detail. For this reason, it lacks the same kind of conceptual organization: we lack terminology to classify them or to reason about their design trade-offs. In this paper, we share our experience in both OS and language-specific package manager development, categorizing families of package managers and discussing their design implications beyond particular implementations. We also identify possibilities in the still largely unexplored area of package manager interoperability.

Since LISP, dynamic languages have supported dynamically-checked type annotations. Even in dynamic languages, these annotations are typically static: tests are restricted to checking low-level features of objects and values, such as primitive types or membership of an explicit programmer-defined class.

We propose much more dynamic types for dynamic languages — first-class objects that programmers can customise, that can be composed with other types and depend on computed values — and to use these first-class type-like values as types. In this way programs can define their own conceptual models of types, extending both the kinds of tests programs can make via types, and the guarantees those tests can provide. Building on a comprehensive pattern-matching system and leveraging standard language syntax lets these types be created, composed, applied, and reused straightforwardly, so programmers can use these truly dynamic first-class types to make their programs easier to read, understand, and debug.

With the increasing need to teach programming to novices using collaborative methods like pair programming, it is important to understand how different input devices can help support collaborative learning. In this paper we present Multi-Device Grace, the first application to explore block-based programming in a cross-device environment consisting of digital tabletops, mobile tablets, and laptops. We conducted a user study (n = 18) to explore how cross-device environments can support co-located collaborative block-based programming. The study used Tiled Grace, an existing block-based programming language, and our extensions: Tabletop Grace (designed for tabletops) and Mobile Grace (designed for tablets). Our results show that the majority of participants felt they were able to collaborate quickly and easily, and the cross device interaction would be particularly beneficial in an education setting.

Function composition is a very natural operation, but most language paradigms provide poor support for it. Without linguistic support programmers must work around or manually implement what would be simple compositions. The Kihi language uses only composition, makes all state visible, and reduces to just six core operations. Kihi programs are easily stepped by textual reduction but provide a foundation for compositional design and analysis.

This article is an apologia for the design of inheritance in the Grace educational programming language: it explains how the design of Grace’s inheritance draws from inheritance mechanisms in predecessor languages, and defends that design as the best of the available alternatives. For simplicity, Grace objects are generated from object constructors, like those of Emerald, Lua, and Javascript; for familiarity, the language also provides classes and inheritance, like Simula, Smalltalk and Java. The design question we address is whether or not object constructors can provide an inheritance semantics similar to classes.

Method names with multiple separate parts are a feature of many dynamic languages derived from Smalltalk. Generalising the syntax of method names to allow parts to be repeated, optional, or alternatives, means a single definition can respond to a whole family of method requests. We show how generalising method names can support flexible APIs for domain-specific languages, complex initialisation tasks, and control structures defined in libraries. We describe how we have extended Grace to support generalised method names, and prove that such an extension can be integrated into a gradually-typed language while preserving type soundness.

“Jigsaw puzzle” programming environments manipulate programs primarily by drag-and-drop. Generally these environments are based on their own special-purpose languages, meaning students must move on to another language as their programs grow. Tiled Grace is a tile-based editor for Grace, an educational programming language with a conventional textual syntax. Using Tiled Grace, programmers can move seamlessly between visualising their programs as tiles or source code, editing their programs via tiles or text, and continue on to traditional textual environments, all within the same programming language. We conducted a user experiment with Tiled Grace, and present the results of that experiment showing that users find dual views helpful.

“Jigsaw puzzle” programming environments manipulate programs primarily by drag-and-drop. Generally these environments are based on their own special-purpose languages, meaning students must move on to another language as their programs grow. Tiled Grace is a tile-based editor for Grace, an educational programming language with a conventional textual syntax. Using Tiled Grace, programmers can move seamlessly between visualising their programs as tiles or source code, editing their programs via tiles or text, and continuing on to traditional textual environments, all within the same programming language.

We are engaged in the design of Grace, a new object-oriented open source programming language aimed at instructors and students in introductory programming courses. Grace aims to include features that have been found useful in software practice, while allowing multiple different teaching approaches without requiring that concepts be introduced to students before they are ready. While many aspects of Grace’s design will be familiar to most object-oriented programmers, Grace cleanly separates the concepts of “object”, “class”, and “type”, and so Grace offers more options for creating objects than most other languages. We have written these patterns to explain how Grace programmers should go about creating objects.

Object orientation and pattern matching are often seen as conflicting approaches to program design. Object-oriented programs place type-dependent behavior inside objects and invoke it via dynamic dispatch, while pattern-matching programs place type-dependent behavior outside data structures and invoke it via multiway conditionals (case statements). Grace is a new, dynamic, object-oriented language designed to support teaching: to this end, Grace needs to support both styles. We explain how this conflict can be resolved grace- fully: by modelling patterns and cases as partial functions, reifying those functions as objects, and then building up complex patterns from simpler ones using pattern combinators. We describe the implementation of this design as an object-oriented framework, and a case study of its effectiveness.

Grace is a new object-oriented programming language aimed at education. Here we describe patterns relating to pattern-matching in this language.