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Algebra of logic programming
 International Conference on Logic Programming
, 1999
"... At present, the field of declarative programming is split into two main areas based on different formalisms; namely, functional programming, which is based on lambda calculus, and logic programming, which is based on firstorder logic. There are currently several language proposals for integrating th ..."
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At present, the field of declarative programming is split into two main areas based on different formalisms; namely, functional programming, which is based on lambda calculus, and logic programming, which is based on firstorder logic. There are currently several language proposals for integrating the expressiveness of these two models of computation. In this thesis we work towards an integration of the methodology from the two research areas. To this end, we propose an algebraic approach to reasoning about logic programs, corresponding to the approach taken in functional programming. In the first half of the thesis we develop and discuss a framework which forms the basis for our algebraic analysis and transformation methods. The framework is based on an embedding of definite logic programs into lazy functional programs in Haskell, such that both the declarative and the operational semantics of the logic programs are preserved. In spite of its conciseness and apparent simplicity, the embedding proves to have many interesting properties and it gives rise to an algebraic semantics of logic programming. It also allows us to reason about logic programs in a simple calculational style, using rewriting and the algebraic laws of combinators. In the embedding, the meaning of a logic program arises compositionally from the meaning of its constituent subprograms and the combinators that connect them. In the second half of the thesis we explore applications of the embedding to the algebraic transformation of logic programs. A series of examples covers simple program derivations, where our techniques simplify some of the current techniques. Another set of examples explores applications of the more advanced program development techniques from the Algebra of Programming by Bird and de Moor [18], where we expand the techniques currently available for logic program derivation and optimisation. To my parents, Sandor and Erzsebet. And the end of all our exploring Will be to arrive where we started And know the place for the first time.
Generic Downwards Accumulations
 Science of Computer Programming
, 2000
"... . A downwards accumulation is a higherorder operation that distributes information downwards through a data structure, from the root towards the leaves. The concept was originally introduced in an ad hoc way for just a couple of kinds of tree. We generalize the concept to an arbitrary regular d ..."
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Cited by 19 (3 self)
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. A downwards accumulation is a higherorder operation that distributes information downwards through a data structure, from the root towards the leaves. The concept was originally introduced in an ad hoc way for just a couple of kinds of tree. We generalize the concept to an arbitrary regular datatype; the resulting denition is coinductive. 1 Introduction The notion of scans or accumulations on lists is well known, and has proved very fruitful for expressing and calculating with programs involving lists [4]. Gibbons [7, 8] generalizes the notion of accumulation to various kinds of tree; that generalization too has proved fruitful, underlying the derivations of a number of tree algorithms, such as the parallel prex algorithm for prex sums [15, 8], Reingold and Tilford's algorithm for drawing trees tidily [21, 9], and algorithms for query evaluation in structured text [16, 23]. There are two varieties of accumulation on lists: leftwards and rightwards. Leftwards accumulation ...
The Many Disguises of Accumulation
, 1991
"... Several descriptions of basically one transformation technique, viz. accumulation, are compared. Their basis, viz. the associativity and the existence of a neutral element inherent in a monoid, is identified. Keywords transformational programming, factorial, fast reverse, accumulation, continuation ..."
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Cited by 7 (0 self)
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Several descriptions of basically one transformation technique, viz. accumulation, are compared. Their basis, viz. the associativity and the existence of a neutral element inherent in a monoid, is identified. Keywords transformational programming, factorial, fast reverse, accumulation, continuations, lambda abstraction, generalisation, tail recursion, implementation of lists. This research has been sponsored by the Netherlands Organisation for Scientific Research (NWO), under grant NF 63/62518 (the STOP  Specification and Transformation Of Programs  project). 1 Introduction One of the first program transformations that appeared in the literature was the accumulation transformation. The transformation is now classic, although not everyone may know it under exactly this name. In this note, I try to relate several descriptions of this program transformation technique. In a purely algebraic view, it is the exploitation of the properties of a monoid. In literature, it can be fou...
Colimits for Concurrent Collectors
 In Verification: Theory and Practice, essays Dedicated to Zohar Manna on the Occasion of His 64th Birthday (2003
, 2003
"... This case study applies techniques of formal program development by specification refinement and composition to the problem of concurrent garbage collection. The specification formalism is mainly based on declarative programming paradigms, the imperative aspect is dealt with by using monads. We ..."
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Cited by 6 (3 self)
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This case study applies techniques of formal program development by specification refinement and composition to the problem of concurrent garbage collection. The specification formalism is mainly based on declarative programming paradigms, the imperative aspect is dealt with by using monads. We also sketch the use of temporal logic in connection with monadic specifications.
ContextMoving Transformations for Function Verification
, 1999
"... Several induction theorem provers have been developed which support mechanized verification of functional programs. Unfortunately, a major problem is that they often fail in verifying tail recursive functions (which correspond to imperative programs). However, in practice imperative programs are ..."
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Cited by 6 (1 self)
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Several induction theorem provers have been developed which support mechanized verification of functional programs. Unfortunately, a major problem is that they often fail in verifying tail recursive functions (which correspond to imperative programs). However, in practice imperative programs are used almost exclusively. We present an automatic transformation to tackle this problem. It transforms functions which are hard to verify into functions whose correctness can be shown by the existing provers. In contrast to classical program transformations, the aim of our technique is not to increase efficiency, but to increase veriability. Therefore, this paper introduces a novel application area for program transformations and it shows that such techniques can in fact solve some of the most urgent current challenge problems in automated verification and induction theorem proving.
On Deforesting Parameters of Accumulating Maps
 In Logic Based Program Synthesis and Transformation, 11th International Workshop, LOPSTR 2001, volume 2372 of LNCS
, 2002
"... Deforestation is a wellknown program transformation technique which eliminates intermediate data structures that are passed between functions. One of its weaknesses is the inability to deforest programs using accumulating parameters. ..."
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Deforestation is a wellknown program transformation technique which eliminates intermediate data structures that are passed between functions. One of its weaknesses is the inability to deforest programs using accumulating parameters.
HigherOrder Transformation of Logic Programs
 In Proceedings of the Tenth International Workshop on Logicbased Program Synthesis and Transformation (LOPSTR 2000
, 2000
"... It has earlier been assumed that a compositional approach to algorithm design and program transformation is somehow unique to functional programming. Elegant theoretical results codify the basic laws of algorithmics within the functional paradigm and with this paper we hope to demonstrate that s ..."
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Cited by 5 (1 self)
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It has earlier been assumed that a compositional approach to algorithm design and program transformation is somehow unique to functional programming. Elegant theoretical results codify the basic laws of algorithmics within the functional paradigm and with this paper we hope to demonstrate that some of the same techniques and results are applicable to logic programming as well.
Flexible Continuations in Logic Programs via Unfold/Fold Transformations and Goal Generalization
 In Proceedings of the 2nd ACM SIGPLAN Workshop on Continuations
, 1997
"... We consider the use of continuations for deriving efficient logic programs. It is known that both in the case of functional and logic programming, the introduction of continuations is a valuable technique for transforming old programs into new, more efficient ones. However, in general, in order to d ..."
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We consider the use of continuations for deriving efficient logic programs. It is known that both in the case of functional and logic programming, the introduction of continuations is a valuable technique for transforming old programs into new, more efficient ones. However, in general, in order to derive programs with high levels of efficiency, one should introduce continuations according to suitable strategies. In particular, we show that it is preferable to introduce continuations in a flexible way, that is, during the process of program transformation itself, rather than at its beginning or at its end. We extend logic programs by allowing variables to range over goals, and we propose a set of transformation rules for this extended language. We propose a generalization strategy for the introduction of goal variables which may be viewed as continuations and they allow for the derivation of very efficient programs. 1 Introduction Continuationbased program transformations [22] have be...