Type specialization can serve as a powerful tool in enforcing safety properties on foreign code. Using the specification of a monitoring interpreter, polyvariant type specialization can produce compiled code that is guaranteed to obey a specified safety policy. It propagates a security state at compile-time and generates code for each different security state. The resulting code contains virtually no run-time operations on the security state, at the price of some code duplication. A novel extension of type specialization by intersection types limits the amount of code duplication considerably, thus making the approach practical. A few years back, mobile code was merely an exciting research subject. Meanwhile, the situation has changed dramatically and mobile code is about to invade our everyday lives. Many applications load parts of their code - or even thirdparty extension modules - from the network and run it on the local computer. Web browsers are the most prominent of these a...

Polyvariant expansion is a binding-time-improving transformation for offline partial evaluation. We show how to achieve it automatically for a higher-order functional language using the interpretive approach. We have designed and implemented an interpreter that statically propagates binding times. When specialized with respect to a source program, it performs polyvariant expansion. Extending the interpreter to an online specializer allows us to generate a binding-time-polyvariant compiler generator. Maintaining the binding times affords an abstract interpretation equivalent to a constraint-based binding-time analysis.

An approach for systematically modifying the semantics of programming languages by semantics modifiers is described. Semantics modifiers are a class of programs that allow the development of general and reusable "semantics components". Language independence is achieved through the interpretive approach: an interpreter serves as a mediator between the new language and the language for which the non-standard semantics was implemented. Inverse computation, equivalence transformation and neighborhood analysis are shown to be semantics modifiers. Experiments with these modifiers show the computational feasibility of this approach. Seven modifier projections are given which allow the e#cient implementation of non-standard interpreters and non-standard compilers by program specialization or other powerful program transformation methods.

Jones optimality tells us that a program specializer is strong enough to remove an entire level of self-interpretation. We show that Jones optimality, which was originally aimed at the Futamura projections, plays an important role in binding-time improvements. The main results show that, regardless of the binding-time improvements which we apply to a source program, no matter how extensively, a specializer that is not Jones-optimal is strictly weaker than a specializer which is Jones optimal. By viewing a binding-time improver as a generating extension of a self-interpreter, we can connect our results with previous work on the interpretive approach.

Interpretation is an implicit part of today’s programming; it has great power but is overused and has significant costs. For example, interpreters are typically significantly hard to understand and hard to reason about. The methodology of “Totally Functional Programming” (TFP) is a reasoned attempt to redress the problem of interpretation. It incorporates an awareness of the undesirability of interpretation with observations that definitions and a certain style of programming appear to offer alternatives to it. Application of TFP is expected to lead to a number of significant outcomes, theoretical as well as practical. Primary among these are novel programming languages to lessen or eliminate the use of interpretation in programming, leading to better-quality software. However, TFP contains a number of lacunae in its current formulation, which hinder development of these outcomes. Among others, formal semantics and type-systems for TFP languages are yet to be discovered, the means to reduce interpretation in programs is to be determined, and a detailed explication is needed of interpretation, definition, and the differences between the two. Most important of all however is the need to develop a complete understanding of the nature of interpretation. In this work, suitable type-systems for TFP languages are identified, and guidance given regarding the construction of appropriate formal semantics. Techniques, based around the ‘fold’ operator, are identified and developed for modifying programs so as to reduce the amount of interpretation they contain. Interpretation as a means of language-extension is also investigated. v Finally, the nature of interpretation is considered. Numerous hypotheses relating to it considered in detail. Combining the results of those analyses with discoveries from elsewhere in this work leads to the proposal that interpretation is not, in fact, symbol-based computation, but is in fact something more fundamental: computation that varies with input. We discuss in detail various implications of this characterisation, including its practical application. An often more-useful property, ‘inherent interpretiveness’, is also motivated and discussed in depth. Overall, our inquiries act to give conceptual and theoretical foundations for practical TFP.