Generic traversals over recursive data structures are often referred to as boilerplate code. The definitions of functions involving such traversals may repeat very similar patterns, but with variations for different data types and different functionality. Libraries of operations abstracting away boilerplate code typically rely on elaborate types to make operations generic. The motivating observation for this paper is that most traversals have value-specific behaviour for just one type. We present the design of a new library exploiting this assumption. Our library allows concise expression of traversals with competitive performance.

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Abstract. In this paper we compare three systems for tracing and debugging Haskell programs: Freja, Hat and Hood. We evaluate their usefulness in practice by applying them to a number of moderately complex programs in which errors had deliberately been introduced. We identify the strengths and weaknesses of each system and then form ideas on how the systems can be improved further.

Abstract. We describe the design and implementation of a system for tracing computations in a lazy functional language. The basis of our tracing method is a program transformation carried out by the compiler: transformed programs compute the same values as the original, but embedded in functional data structures that also include redex trails showing how the values were obtained. A special-purpose display program enables detailed but selective exploration of the redex trails, with cross-links to the source program.

We describe the design, implementation and use of a new kind of profiling tool that yields valuable information about the memory use of lazy functional programs. The tool has two parts: a modified functional language implementation which generates profiling information during the execution of programs, and a separate program which converts this information to graphical form. With the aid of profile graphs, one can make alterations to a functional program which dramatically reduce its space consumption. We demonstrate this in the case of a genuine example -the first to which the tool was applied -for which the results are strikingly successful. Capsule reviewProfiling technology for lazy functional programs is long overdue. Runciman and Wakeling have produced a practical and useful tool, notably because it works in the context of a fullyfledged compiler. Their work highlights the lack of information we have about the dynamic behaviour of lazy functional programs and the potential performance improvements which may be possible given profiling tools to provide us with it. This paper opens up new areas of practical research designing and building such tools.Runciman and Wakeling have started this work with the design and implementation of a heap profiling tool. They place considerable emphasis on the design of an appropriate graphical presentation of the large quantity of profiling data produced. It is interesting that they profile space and not time; ideally one would like both. An upper bound on execution time improvements from improving space behaviour is the garbage collection and paging time. However, they found that the task of fixing space bugs does sometimes lead to beneficial algorithmic changes too.We await with interest the continued development of practical profiling tools for lazy functional programs.