In functional programming, intermediate data structures are often used to "glue" together small programs. Deforestation is a program transformation to remove these intermediate data structures automatically. We present a simple algorithm for deforestation based on two fusion rules for hylomorphism, an expressive recursion pattern. A generic notation for hylomorphisms is introduced, where natural transformations are explicitly factored out, and it is used to represent programs. Our method successfully eliminates intermediate data structures of any algebraic type from a much larger class of compositional functional programs than previous techniques. 1 Introduction In functional programming, programs are often constructed by "gluing" together small components, using intermediate data structures to convey information between them. Such data are constructed in one component and later consumed in another component, but never appear in the result of the whole program. The compositional styl...

Languages that integrate functional and logic programming with a complete operational semantics are based on narrowing, a unification-based goal-solving mechanism which subsumes the reduction principle of functional languages and the resolution principle of logic languages. Formal methods of transformation of functional logic programs can be based on this well-established operational semantics. In this paper, we present a partial evaluation scheme for functional logic languages based on an automatic unfolding algorithm which builds narrowing trees. We study the semantic properties of the transformation and the conditions under which the technique terminates, is sound and complete, and is also generally applicable to a wide class of programs. We illustrate our method with several examples and discuss the relation with Supercompilation and Partial Evaluation. To the best of our knowledge this is the first formal approach to partial evaluation of functional logic programs.

. The aim of this work is to compute descriptions of successful computation paths in logic or functional program executions. Computation paths are represented as terms, built from special constructor symbols, each constructor symbol corresponding to a specific clause or equation in a program. Such terms, called trace-terms, are abstractions of computation trees, which capture information about the control flow of the program. A method of approximating trace-terms is described, based on well-established methods for computing regular approximations of terms. The special function symbols are first introduced into programs as extra arguments in predicates or functions. Then a regular approximation of the program is computed, describing the terms occurring in some set of program executions. The approximation of the extra arguments (the trace-terms) can then be examined to see what computation paths were followed during the computation. This information can then be used to control both off-l...

We compare transformations for the elimination of intermediate results in first-order functional programs. We choose the well known deforestation technique of Wadler and composition techniques from the theory of tree transducers, of which the implementation of functional programs yet does not take advantage. We identify syntactic classes of function definitions for which both techniques deliver equally efficient results and for which one technique is more powerful than the other.

Functional programming languages are an ideal medium for program optimisations based on source-to-source transformation techniques. Referential transparency affords opportunities for a wide range of correctness-preserving transformations leading to potent optimisation strategies. This thesis builds on deforestation, a program transformation technique due to Wadler that removes intermediate data structures from first-order functional programs. Our contribution is to reformulate deforestation for higher-order functional programming languages, and to show that the resulting algorithm terminates given certain syntactic and typing constraints on the input. These constraints are entirely reasonable, indeed it is possible to translate any typed program into the required syntactic form. We show how this translation can be performed automatically and optimally. The higher-order deforestation algorithm is transparent. That is, it is possible to determine by examination of the source program w...

We show that the power of supercompilation can be increased by constructing a hierarchy of supercompilers, in which a lower-level supercompiler is used by a higher-level one for proving improvement lemmas. The lemmas thus obtained are used to transform expressions labeling nodes in process trees, in order to avoid premature generalizations. Such kind of supercompilation, based on a combination of several metalevels, is called higher-level supercompilation (to differentiate it from higher-order supercompilation related to transforming higher-order functions). Higher-level supercompilation may be considered as an application of a more general principle of metasystem transition.

Supercompilation is a technique due to Turchin [1] which allows for the construction of program optimisers that are both simple and extremely powerful. Supercompilation is capable of achieving transformations such as deforestation [2], function specialisation and constructor specialisation [3]. Inspired by Mitchell’s promising results [4], we show how the call-by-need supercompilation algorithm can be recast to be based explicitly on an evaluator, and in the process extend it to deal with recursive let expressions.

The dominant approach to model-driven development and domain-specific language engineering is to write a translator, or compiler, that defines a strategy for executing the high-level language. In this paper we introduce a new approach to strategic programming by writing interpreters of high-level modeling languages, rather than compilers. This technique is demonstrated by interpreting data models and user interface models. The interpreters are compiled by partial evaluation and deforestation. Although partial evaluation is traditionally applied to functions, we show that it can also be applied to implement data abstractions as objects. Generic functions, for equality and reading, can also be defined as interpreters and partially evaluated. The user interface interpreter illustrates a solution to integrating two modeling languages. The system described here is bootstrapped from Scheme, although the goal is to build a complete software development environment based on model interpretation.

Languages that integrate functional and logic programming with a complete operational semantics are based on narrowing, a unification-based goal-solving mechanism which subsumes the reduction principle of functional languages and the resolution principle of logic languages. In this article, we present a partial evaluation scheme for functional logic languages based on an automatic unfolding algorithm which builds narrowing trees. The method is formalized within the theoretical framework established by Lloyd and Shepherdson for the partial deduction of logic programs, which we have generalized for dealing with functional computations. A generic specialization algorithm is proposed which does not depend on the eager or lazy nature of the narrower being used. To the best of our knowledge, this is the first generic algorithm for the specialization of functional logic programs. We study the semantic properties of the transformation and the conditions under which the technique terminates, is...

Supercompilation is a powerful technique for program optimisation and theorem proving. In this paper we describe and evaluate three improvements to the Cambridge Haskell Supercompiler (CHSC). We reduce supercompiled program size by the use of a weak normaliser and aggressive rollback, and we improve the performance of supercompiled programs by heap speculation and generalisation. Our generalisation method is simpler than those in the literature, and is better at generalising computations involving primitive operations such as those on machine integers. We also provide the first comprehensive account of the tag-bag termination mechanism.