Linear, bounded, functional pretty-printing

We present two implementations of Oppen's pretty-printing algorithm in Haskell that meet the efficiency of Oppen's imperative solution but have a simpler, clear structure. We start with an implementation that uses lazy evaluation to simulate two co-operating processes. Then we present an implementation that uses higher-order functions for delimited continuations to simulate co-routines with explicit scheduling

Fine-grained visualization pipelines and lazy functional languages

The pipeline model in visualization has evolved from a conceptual model of data processing into a widely used architecture for implementing visualization systems. In the process, a number of capabilities have been introduced, including streaming of data in chunks, distributed pipelines, and demand-driven processing. Visualization systems have invariably built on stateful programming technologies, and these capabilities have had to be implemented explicitly within the lower layers of a complex hierarchy of services. The good news for developers is that applications built on top of this hierarchy can access these capabilities without concern for how they are implemented. The bad news is that by freezing capabilities into low-level services expressive power and flexibility is lost. In this paper we express visualization systems in a programming language that more naturally supports this kind of processing model. Lazy functional languages support fine-grained demand-driven processing, a natural form of streaming, and pipeline-like function composition for assembling applications. The technology thus appears well suited to visualization applications. Using surface extraction algorithms as illustrative examples, and the lazy functional language Haskell, we argue the benefits of clear and concise expression combined with fine-grained, demand-driven computation. Just as visualization provides insight into data, functional abstraction provides new insight into visualization

FliPpr: A Prettier Invertible Printing System

When implementing a programming language, we often write a parser and a pretty-printer. However, manually writing both programs is not only tedious but also error-prone; it may happen that a pretty-printed result is not correctly parsed. In this paper, we propose FliPpr, which is a program transformation system that uses program inversion to produce a CFG parser from a pretty-printer. This novel approach has the advantages of fine-grained control over pretty-printing, and easy reuse of existing efficient pretty-printer and parser implementations

A pretty-printer for every occasion

Tool builders dealing with many different languages, and language designers require sophisticated pretty-print techniques to minimize the time needed for constructing and adapting pretty-printers. We combined new and existing pretty-print techniques in a generic pretty-printer that satisfies modern pretty-print requirements. Its features include language independence, customization, and incremental pretty-printer generation. Furthermore, we emphasize that the recent acceptance of XML as international standard for the representation of structured data demands flexible pretty-print techniques, and we demonstrate that our pretty-printer provides such technology

Maximum Segment Sum, Monadically (distilled tutorial, with solutions)

The maximum segment sum problem is to compute, given a list of integers, the largest of the sums of the contiguous segments of that list. This problem specification maps directly onto a cubic-time algorithm; however, there is a very elegant linear-time solution too. The problem is a classic exercise in the mathematics of program construction, illustrating important principles such as calculational development, pointfree reasoning, algebraic structure, and datatype-genericity. Here, we take a sideways look at the datatype-generic version of the problem in terms of monadic functional programming, instead of the traditional relational approach; the presentation is tutorial in style, and leavened with exercises for the reader.Comment: Revision of the article in Proceedings DSL 2011, EPTCS 66, arXiv:1109.0323, to provide solutions to the exercise

Pretty-printing within the ASF+SDF meta-environment : a generic approach

The automatic generation of formatters for (programming) languages within the Asf+Sdf Meta-Environment is a research topic that is concerned with the construction of language specific formatters (or pretty-printers) given a language definition in Sdf. In this paper, we give an overview of pretty-printers that have been developed within this project and observe that these pretty-printers are either language dependent or non-customizable. Language independence and customizability are inevitable properties of pretty-printers however, when faced with the problem of formatting many different, evolving languages. Therefore, we introduce in this paper a generic framework for pretty-printing and describe an instantiation of the framework that forms a language independent and customizable pretty-printer

Encoding types in ML-like languages

AbstractThis article presents several general approaches to programming with type-indexed families of values within a Hindley–Milner type system. A type-indexed family of values is a function that maps a family of types to a family of values. The function performs a case analysis on the input types and returns values of possibly different types. Such a case analysis on types seems to be prohibited by the Hindley–Milner type system. Our approaches solve the problem by using type encodings. The compile-time types of the type encodings reflect the types themselves, thereby making the approaches type-safe, in the sense that the underlying type system statically prevents any mismatch between the input type and the function arguments that depend on this type.A type encoding could be either value-dependent, meaning that the type encoding is tied to a specific type-indexed family, or value-independent, meaning that the type encoding can be shared by various type-indexed families. Our first approach is value-dependent: we simply interpret a type as its corresponding value. Our second approach provides value-independent type encodings through embedding and projection functions; they are universal type interpretations, in that they can be used to compute other type interpretations. We also present an alternative approach to value-independent type encodings, using higher-order functors.We demonstrate our techniques through applications such as C printf-like formatting, type-directed partial evaluation, and subtype coercions