Strategic polymorphism requires just two combinators!

In previous work, we introduced the notion of functional strategies: first-class generic functions that can traverse terms of any type while mixing uniform and type-specific behaviour. Functional strategies transpose the notion of term rewriting strategies (with coverage of traversal) to the functional programming paradigm. Meanwhile, a number of Haskell-based models and combinator suites were proposed to support generic programming with functional strategies. In the present paper, we provide a compact and matured reconstruction of functional strategies. We capture strategic polymorphism by just two primitive combinators. This is done without commitment to a specific functional language. We analyse the design space for implementational models of functional strategies. For completeness, we also provide an operational reference model for implementing functional strategies (in Haskell). We demonstrate the generality of our approach by reconstructing representative fragments of the Strafunski library for functional strategies.Comment: A preliminary version of this paper was presented at IFL 2002, and included in the informal preproceedings of the worksho

Strategic polymorphism requires just two combinators!

In previous work, we introduced the notion of functional strategies: first-class generic functions that can traverse terms of any type while mixing uniform and type-specific behaviour. Functional strategies transpose the notion of term rewriting strategies (with coverage of traversal) to the functional programming paradigm. Meanwhile, a number of Haskell-based models and combinator suites were proposed to support generic programming with functional strategies. In the present paper, we provide a compact and matured reconstruction of functional strategies. We capture strategic polymorphism by just two primitive combinators. This is done without commitment to a specific functional language. We analyse the design space for implementational models of functional strategies. For completeness, we also provide an operational reference model for implementing functional strategies (in Haskell). We demonstrate the generality of our approach by reconstructing representative fragments of the Strafunski library for functional strategies

PARALLELIZING TIME-SERIES SESSION DATA ANALYSIS WITH A TYPE-ERASURE BASED DSEL

The Science Information Network (SINET) is a Japanese academic backbone network.  SINET consists of more than 800 universities and research institutions.  In the operation of a huge academic backbone network, more flexible querying technology is required to cope with massive time series session data and analysis of sophisticated cyber-attacks. This paper proposes a parallelizing DSEL (Domain Specific Embedded Language) processing for huge time-series session data. In our DESL, the function object is implemented by type erasure for constructing internal DSL for processing time-series data. Type erasure enables our parser to store function pointer and function object into the same *void type with class templates. We apply to scatter/gather pattern for concurrent DSEL parsing. Each thread parses DSEL to extract the tuple timestamp, source IP, and destination IP in the gather phase. In the scattering phase, we use a concurrent hash map to handle multiple thread outputs with our DSEL. In the experiment, we have measured the elapsed time in parsing and inserting IPv4 address and timestamp data format ranging from 1,000 to 50,000 lines with 24-row items. We have also measured CPU idle time in processing 100,000,000 lines of session data with 5, 10 and 20 multiple threads. It has been turned out that the proposed method can work in feasible computing time in both cases

Strong (X)HTML Compliance with Haskell\u27s Flexible Type System

We report on the embedding of a domain specific language, (X)HTML, into Haskell and demonstrate how this superficial non-context-free language can be represented and rendered to guarantee World Wide Web Consortium (W3C) compliance. Compliance of web content is important for the health of the Internet, accessibility, visibility, and reliable search. While tools exist to verify web content is compliant according to the W3C, few systems guarantee that all produced content is compliant. We present CH-(X)HTML, a library for generating compliant (X)HTML content by using Haskell to encode the nontrivial syntax of (X)HTML set forth by the W3C. Any compliant document can be represented with this library, while a compilation error will occur if non-compliant markup is attempted. To demonstrate our library we present examples and performance measurements

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

Encoding Types in ML-like Languages (Preliminary Version)

A Hindley-Milner type system such as ML's seems to prohibit typeindexed values, i.e., functions that map a family of types to a family of values. Such functions generally perform case analysis on the input types and return values of possibly different types. The goal of our work is to demonstrate how to program with type-indexed values within a Hindley-Milner type system.Our first approach is to interpret an input type as its correspondingvalue, recursively. This solution is type-safe, in the sense that the ML type system statically prevents any mismatch between the input type and function arguments that depend on this type.Such specific type interpretations, however, prevent us from combining different type-indexed values that share the same type. To meet this objection, we focus on finding a value-independent type encoding that can be shared by different functions. We propose and compare two solutions. One requires first-class and higher-order polymorphism, and, thus, is not implementable in the core language of ML, but itcan be programmed using higher-order functors in Standard ML of New Jersey. Its usage, however, is clumsy. The other approach uses embedding/projection functions. It appears to be more practical. We demonstrate the usefulness of type-indexed values through examples including type-directed partial evaluation, C printf-like formatting, and subtype coercions. Finally, we discuss the tradeoffs between our approach and some other solutions based on more expressive typing disciplines

Modular Normalization with Types

With the increasing use of software in today’s digital world, software is becoming more and more complex and the cost of developing and maintaining software has skyrocketed. It has become pressing to develop software using effective tools that reduce this cost. Programming language research aims to develop such tools using mathematically rigorous foundations. A recurring and central concept in programming language research is normalization: the process of transforming a complex expression in a language to a canonical form while preserving its meaning. Normalization has compelling benefits in theory and practice, but is extremely difficult to achieve. Several program transformations that are used to optimise programs, prove properties of languages and check program equivalence, for instance, are after all instances of normalization, but they are seldom viewed as such.Viewed through the lens of current methods, normalization lacks the ability to be broken into sub-problems and solved independently, i.e., lacks modularity. To make matters worse, such methods rely excessively on the syntax of the language, making the resulting normalization algorithms brittle and sensitive to changes in the syntax. When the syntax of the language evolves due to modification or extension, as it almost always does in practice, the normalization algorithm may need to be revisited entirely. To circumvent these problems, normalization is currently either abandoned entirely or concrete instances of normalization are achieved using ad hoc means specific to a particular language. Continuing this trend in programming language research poses the risk of building on a weak foundation where languages either lack fundamental properties that follow from normalization or several concrete instances end up repeated in an ad hoc manner that lacks reusability.This thesis advocates for the use of type-directed Normalization by Evaluation (NbE) to develop normalization algorithms. NbE is a technique that provides an opportunity for a modular implementation of normalization algorithms by allowing us to disentangle the syntax of a language from its semantics. Types further this opportunity by allowing us to dissect a language into isolated fragments, such as functions and products, with an individual specification of syntax and semantics. To illustrate type-directed NbE in context, we develop NbE algorithms and show their applicability for typed programming language calculi in three different domains (modal types, static information-flow control and categorical combinators) and for a family of embedded-domain specific languages in Haskell