I started studying computer science at the RWTH Aachen in 1989. I spent the academic year 1992/93 as an Erasmus exchange student at the University of Kent at Canterbury. I graduated in Aachen in June 1995, writing a dissertation about semantics of functional programs. From August 1995 to May 2000 I was employed as research & teaching assistant at the Lehrstuhl für Informatik II at the RWTH Aachen. There I obtained my PhD with a thesis about type-based deforestation of functional programs. Afterwards I came to the University of York as a research associate. Together with Colin Runciman and Malcolm Wallace I developed the Haskell tracer Hat. In 2002 I became a teaching fellow in York. In 2004 I became lecturer at the University of Kent.
As the Lecturer [...] put it: `He [the Archchancellor] called me in and asked me what I did, exactly. Have you ever heard of such a thing? What sort of question is that? This is a university!'
Terry Pratchett, The Last Continent
Besides computer science I enjoy walking, reading, gardening, visiting historical sites and travelling in general.
I belong to the following research groups:
All my research interests are connected to programming and programming languages. I am interested in semantics and theoretical foundations of programming languages, type theory, program transformation, compiler construction, message-passing-based concurrency, programming tools, and how to write programs. I aim to support programmers in developing software more effectively. My favourite programming languages are functional languages, especially Haskell.
Algorithms and Logic - COMP8840
Foundations of Computing II - COMP3250
Do you want to do a PhD? Are you interested in functional programming languages or related topics? Then I would be pleased to hear from you.
General chair and local organiser together with Andy King of PPDP 2014 and LOPSTR 2014.
Programme committee chair of IFL 2007.
Programme committee member of Haskell Symposium 2018, WFLP 2018, WFLP 2017, PEPM 2016, LOPSTR 2015, TFP 2015, SLE 2013, ICFP 2013, Haskell Symposium 2013, IFL 2011, DSL 2011, WFLP 2011, TFP 2011, IFL 2010, PADL 2010, IFL 2008, TFP 2006, WCFLP 2005, WFLP 2004, Haskell Workshop 2003, WFLP 2003, IFL 2002, IFL 2001.
I am a member of the PPDP steering commitee. I am also a member of the IFL advisory committee. A long time ago I co-maintained the Haskell Home Page.
I gave the invited talk at PROLE 2013.
is a source-level tracer for Haskell. Often, programmers find it difficult to understand how the different parts of a program cause the computation to perform the observed input/output actions. Hat enables a user to see and interactively explore the usually invisible computation. Thus Hat assists with debugging, understanding complex programs (which we may not have written ourselves) and is useful for teaching.
- A library for practical typed lazy contracts for Haskell
is a Haskell library for writing assertions that are both prompt and lazy. Properties are formulated in a monadic, parser-combinator-like language. See the APLAS 2007 paper for further information.
is a tool that tests whether a given Haskell function is least-strict. If it is not, StrictCheck suggests how the function could be less strict. See my IFL 2006 paper, slides and later technical report for further information.Chasing Bottoms library and the Glasgow Haskell compiler.
is a library plus viewing tool for lightweight debugging of functional logic programs in Curry by observations. The programmer annotates expressions of interest in their program. With the viewing tool the programmer then views the values the annotated expressions have in a computation.
is a prototype tool implementing the ideas presented in the paper Compositional Explanation of Types and Algorithmic Debugging of Type Errors. It constructs the type explanation graph for programs written in a simple Haskell-like language and enables free navigation through the graph in various ways and algorithmic debugging.
is a Haskell library for pretty printing. The library has the same interface as that of Wadler. It is very efficient, in contrast to Wadler's library and the one by John Hughes and Simon Peyton Jones the pretty printer only takes time linear in the size of the printed document; it does not do any backtracking. This version is based on the latest papers by Doaitse Swierstra and me but provides additional combinators following PPrint by Daan Leijen.