Design and quality are fundamental themes in engineering education. Functionalprogramming builds software from small components, a central element of gooddesign, and facilitates reasoning about correctness, an important aspect ofquality. Software engineering courses that employ functional programming providea platform for educating students in the design of quality software. This pearldescribes experiments in the use of ACL2, a purely functional subset of CommonLisp with an embedded mechanical logic, to focus on design and correctness insoftware engineering courses. Students find the courses challenging andinteresting. A few acquire enough skill to use an automated theorem prover onthe job without additional training. Many students, but not quite a majority,find enough success to suggest that additional experience would make themeffective users of mechanized logic in commercial software development. Nearlyall gain a new perspective on what it means for software to be correct andacquire a good understanding of functional programming.

Delimited continuations are more expressive than traditional abortive continuations and they apparently require a framework beyond traditional continuation-passing style (CPS). We show that this is not the case: standard CPS is sufficient to explain the common control operators for delimited continuations. We demonstrate this fact and present an implementation as a Scheme library. We then investigate a typed account of delimited continuations that makes explicit where control effects can occur. This results in a monadic framework for typed and encapsulated delimited continuations, which we design and implement as a Haskell library.

Monads are commonplace programming devices that are used to uniformly structure computations; in particular, they are often used to mimic the effects of impure features such as state, error handling, and I/O. This paper further develops the monadic programming paradigm by investigating the extent to which monadic computations can be optimised by using generalisations of short cut fusion to eliminate monadic structures whose sole purpose is to “glue together” monadic program components. Ghani, Uustalu, and Vene have recently shown that every inductive type has an associated build combinator and an associated short cut fusion law. They have also used the notion of a parameterised monad to describe those monads that give rise to inductive types, and have shown that the standard augment combinators and cata/augment fusion rules for algebraic data types can be generalised to fixed points of all parameterised monads. We revisit these augment combinators and generalised short cut fusion rules for such types but consider them from a functional programming perspective, rather than a categorical one. In addition to making the category-theoretic ideas of Ghani, Uustalu, and Vene more easily accessible to a wider audience of functional programmers, we demonstrate their practical applicability by developing nontrivial application programs and performing modest benchmarking on them. We also show how the cata/augment rules can serve as the basis for deriving additional generic fusion laws, thus opening the way for an algebra of fusion. Finally, we offer deep theoretical insights, arguing that the augment combinators are monadic in nature, and thus that the cata/build and cata/augment rules are arguably the best generally applicable fusion rules obtainable.

Asynchronous exceptions, or interrupts, are important for writing robust, modular programs, but are traditionally viewed as being difficult from a semantic perspective. In this article, we present a simple, formally justified, semantics for interrupts. Our approach is to show how a high-level semantics for interrupts can be justified with respect to a low-level implementation, by means of a compiler and its correctness theorem. In this manner we obtain two different perspectives on the problem, formally shown to be equivalent, which gives greater confidence in the correctness of our semantics.

We bridge two distinct approaches to one-pass CPS transformations, i.e, CPS transformations that reduce administrative redexes at transformation time instead of in a post-processing phase. One approach is compositional and higher-order, and is independently due to Appel, Danvy and Filinski, and Wand, building on Plotkin's seminal work. The other is non-compositional and based on a reduction semantics for the lambda-calculus, and is due to Sabry and Felleisen. To relate the two approaches, we use three tools: Reynolds's defunctionalization and its left inverse, refunctionalization; a special case of fold–unfold fusion due to Ohori and Sasano, fixed-point promotion; and an implementation technique for reduction semantics due to Danvy and Nielsen, refocusing. This work is directly applicable to transforming programs into monadic normal form.