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Live coding focuses on improvising content by coding in textual interfaces, but this reliance on low level text editing impairs usability by not allowing for high level manipulation of content. VJing focuses on remixing existing content with graphical user interfaces and hardware controllers, but this focus on high level manipulation does not allow for fine-grained control where content can be improvised from scratch or manipulated at a low level. This thesis proposes the code jockey practice (CJing), a new hybrid practice that combines aspects of live coding and VJing practice. In CJing, a performer known as a code jockey (CJ) interacts with code, graphical user interfaces and hardware controllers to create or manipulate real-time visuals. CJing harnesses the strengths of live coding and VJing to enable flexible performances where content can be controlled at both low and high levels. Live coding provides fine-grained control where content can be improvised from scratch or manipulated at a low level while VJing provides high level manipulation where content can be organised, remixed and interacted with. To illustrate CJing, this thesis contributes Visor, a new environment for live visual performance that embodies the practice. Visor's design is based on key ideas of CJing and a study of live coders and VJs in practice. To evaluate CJing and Visor, this thesis reflects on the usage of Visor in live performances and feedback gathered from creative coders, live coders, and VJs who experimented with the environment.

Though some software development teams are highly effective at delivering security, others either do not care or do not have access to security experts to teach them how. Unfortunately, these latter teams are still responsible for the security of the systems they build: systems that are ever more important to ever more people. We propose that a series of lightweight interventions, six hours of facilitated workshops delivered over three months, can improve a team’s motivation to consider security and awareness of assurance techniques, changing its security culture even when no security experts are involved. The interventions were developed after an Appreciative Inquiry and Grounded Theory survey of security professionals to find out what approaches work best. They were then validated in fieldwork with a Participatory Action Research study that de-livered the workshops to three development organizations. This approach has the potential to be applied by many development teams, improving the security of software worldwide.

Though some software development teams are highly effective at delivering security, others either do not care or do not have access to security experts to teach them how. Unfortunately, these latter teams are still responsible for the security of the systems they build: systems that are ever more important to ever more people. We propose that a series of lightweight interventions, six hours of facilitated workshops delivered over three months, can improve a team’s motivation to consider security and awareness of assurance techniques, changing its security culture even when no security experts are involved. The interventions were developed after an Appreciative Inquiry and Grounded Theory survey of security professionals to find out what approaches work best. They were then validated in fieldwork with a Participatory Action Research study that de-livered the workshops to three development organizations. This approach has the potential to be applied by many development teams, improving the security of software worldwide.

One form of type checking used in gradually typed language is transient type checking: whenever an object 'flows' through code with a type annotation, the object is dynamically checked to ensure it has the methods required by the annotation. Just-in-time compilation and optimisation in virtual machines can eliminate much of the overhead of run-time transient type checks. Unfortunately this optimisation is not uniform: some type checks will significantly decrease, or even increase, a program's performance. In this paper, we refine the so called "Takikawa" protocol, and use it to identify which type annotations have the greatest effects on performance. In particular, we show how graphing the performance of such benchmarks when varying which type annotations are present in the source code can be used to discern potential patterns in performance. We demonstrate our approach by testing the Moth virtual machine: for many of the benchmarks where Moth's transient type checking impacts performance, we have been able to identify one or two specific type annotations that are the likely cause. Without these type annotations, the performance impact of transient type checking becomes negligible. Using our technique programmers can optimise programs by removing expensive type checks, and VM engineers can identify new opportunities for compiler optimisation.

Effect systems are used to statically reason about the effects an expression may have when evaluated. In the literature, such effects include various behaviours as diverse as memory accesses and exception throwing. Here we present CallE, an object-oriented language that takes a flexible approach where effects are just method calls: this works well because ordinary methods often model things like I/O operations, access to global state, or primitive language operations such as thread creation. CallE supports both flexible and fine-grained control over such behaviour, in a way designed to minimise the complexity of annotations. CallE's effect system can be used to prevent OO code from performing privileged operations, such as querying a database, modifying GUI widgets, exiting the program, or performing network communication. It can also be used to ensure determinism, by preventing methods from (indirectly) calling non-deterministic primitives like random number generation or file reading.

Transient gradual typing imposes run-time type tests that typically cause a linear slowdown. This performance impact discourages the use of type annotations because adding types to a program makes the program slower. A virtual machine can employ standard just-in-time optimizations to reduce the overhead of transient checks to near zero. These optimizations can give gradually-typed languages performance comparable to state-of-the-art dynamic languages, so programmers can add types to their code without affecting their programs' performance.