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. Keywords: debugging, graph reduction, Haskell, program transformation. 1 Introduction 1.1 Why trace functional computations? Functional programming languages have many advantages over the conventional alternative of procedural languages. For example, program construction is more rapid, more modular and less error-prone. Programs themselves are more concise. Yet functional programming systems are not very widely used. There are various reasons for this, but one that crops up time ...

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