294 papers · page 13 of 15
The Haskell programming language is more-or-less divided into two "branches". The Haskell 98 standard is the "stable" branch of the language, and that has been a big success. A lot of progress has been made over the last few years in the "research" branch of the Haskell language.…
In languages that support polymorphic variants, a single variant value can be passed to many contexts that accept different sets of constructors. Polymorphic variants can be used in order to introduce extensible algebraic datatypes into functional programming languages and are po…
In this article we present GenI, a chart based surface realisation tool implemented in Haskell. GenI takes as input a set of first order terms (the input semantics) and a grammar for a given target language (e.g., English, French, Spanish, etc.) and generates sentences in the tar…
In this paper we address the lack of extensibility of the exception type in Haskell. We propose a lightweight solution involving the use of existential types and the Typeable class only, and show how our solution allows a fully extensible hierarchy of exception types to be declar…
Haskell programmers who deal with complex data types often need to apply functions to specific nodes deeply nested inside of terms. Typically, implementations for those applications require so-called boilerplate code, which recursively visits the nodes and carries the functions t…
Haskell's type system with multi-parameter constructor classes and functional dependencies allows static (compile-time) computations to be expressed by logic programming on the level of types. This emergent capability has been exploited for instance to model arbitrary-length tupl…
Correct handling of concurrently accessed external resources is a demanding problem in programming. The standard approaches rely on database transactions or concurrency mechanisms like locks. The paper considers two such resources, global variables and databases, and defines tran…
Some type class instances can be automatically derived from the structure of types. As a result, the Haskell language includes the "deriving" mechanism to automatic generates such instances for a small number of built-in type classes. In this paper, we present RepLib, a GHC libra…
Program errors are hard to detect and are costly both to programmers who spend significant efforts in debugging, and to systems that are guarded by runtime checks. Extended static checking can reduce these costs by helping to detect bugs at compile-time, where possible. Extended …
Proof assistants based on dependent type theory are closely related to functional programming languages, and so it is tempting to use them to prove the correctness of functional programs. In this paper, we show how Agda, such a proof assistant, can be used to prove theorems about…
Invertible programming occurs in the area of data conversion where it is required that the conversion in one direction is the inverse of the other. For that purpose, we introduce bidirectional arrows (bi-arrows). The bi-arrow class is an extension of Haskell's arrow class with an…
We describe the design and implementation of a full-featured Haskell development environment, based on Microsoft's extensible Visual Studio environment.Visual Haskell provides a number of features not found in existing Haskell development environments: interactive error-checking,…
Calculational developments of functional programs have been likened to conjuring tricks: enjoyable to watch but often a mystery as to how they are done. This pearl explains the trick. The aim is to give new calculations of two famous algorithms in string matching, the Knuth-Morri…
Haskell Server Pages (HSP) is a domain specific language, based on Haskell, for writing dynamic web pages. Its main features are concrete XML expressions as first class values, pattern-matching on XML, and a runtime system for evaluating dynamic web pages.The first design of HSP …
Multi-core processors are coming, and we need ways to program them. The combination of purely-functional programming and explicit, monadic threads, communicating using transactional memory, looks like a particularly promising way to do so. This paper describes a full-scale implem…
In the course of developing a web server for an embedded operating system, we had need of a filesystem which was small enough to alter to our needs and written in a high-level language so that we could show certain high assurance properties about its behavior. Since we had alread…
A type-indexed function is a function that is defined for each member of some family of types. Haskell's type class mechanism provides collections of open type-indexed functions, in which the indexing family can be extended by defining a new type class instance but the collection…
A common reaction from people who hear about darcs, the source control system I created, is that it sounds like a great tool, but it is a shame that it is written in Haskell. People think that because darcs is written in Haskell it will be a slow memory hog with very few contribu…
Haskell has proved itself to be a suitable implementation language for large software projects. Nevertheless, surprisingly few graphical end-user applications have been written in Haskell. Based on our experience with the development of the Bayesian network toolbox Dazzle, we arg…
Abstract The Curry-Howard isomorphism states that types are propositionsand that programs are proofs. This allows programmers to state and enforce invariants of programs by using types. Unfortunately,the type systems of today's functional languages cannot directly express interes…