• Who I am and what I do.
• Current work.
• The Computing at School Working Group
• The Glasgow Haskell Compiler.
• The C-- project
• My publications, and some of those of my students.
• Research skills: how to write a good research paper, give a good research talk, and write a good grant proposal.
• My Win32 cheat sheet

My GPG key fingerprint is: CABA 2C32 0D13 B715 8611 0390 6B2B 1815 5F25 C538

Current work

There is a Wiki talk page on which you are most welcome to discuss or offer constructive feedback on any of these papers.

• New papers
  • [July 2015] Injective type families for Haskell, with Jan Stolarek and Richard Eisenberg, Haskell Symposium 2015.
  • [July 2015] GADTs meet their match: Pattern-matching warnings that account for GADTs, guards, and laziness, with Georgios Karachalias, Tom Schrijvers, and Dimitrios Vytiniotis. ICFP 2015.
  • [June 2014] Refinement types for Haskell, with Niki Vazou, Eric Seidel, Ranjit Jhala, Dimitrios Vytiniotis, ICFP 2014.  Here we describe Liquid Haskell, and in particular how to adapt refinement types for a lazy language.
  • [Apr 2014] Call arity, by Joachim Breitner.   This interesting new analysis is in GHC; Joachim implemented it during an internship at MSR.
  • [June 2014] Safe zero-cost coercions for Haskell, with Joachim Breitner, Richard Eisenberg, and Stephanie Weirich.  Describes the new Coercible mechanism that allows zero-cost coercions between deeply-nested newtypes.
  • [July 2013] Backpack: retrofitting Haskell with interfaces, with Scott Kilpatrick, Derek Dreyer and Simon Marlow.  An exploration of a mixin-module approach to separate modular development (SMD) for Haskell.  In submission.
  • [July 2013] Higher order cardinality analysis in theory and practice,with Ilya Sergy and Dimitrios Vytiniotis, describes an analysis that detects when a lambda is called at most once, or a thunk is used at most once, and shows how to exploit that information to generate better code. Much improved version 2! In submission.
  • [July 2013] Closed type families with overlapping equations, with Richard Eisenberg,
    Dimitrios Vytiniotis, and Stephanie Weirich.  In submission.
  • [June 2013] Composable scheduler activations for Haskell, with KC Sivaramakrishnan, Tim Harris, and Simon Marlow.  This paper gives a new design for our long-standing goal of allowing user-written schedulers in concurrent/parallel Haskell.
  • [May 2013] Computing at school  in the UK, with Simon Humphreys and Bill Mitchell; submitted to CACM.  This paper summarises the rapid and radical developments during 2012-2013 in the K-12 school computing curriculum in UK. We draw out lessons from
    our experience that may be useful to others.
  • [May 2013] Call-by-need supercompilation, PhD thesis, Max Bolingbroke, Cambridge University, May 2013.  Max's thesis summarises three years work on supercompilation as an optimisation technique. Lots of great insights.
  • [Apr 2013] Equality normalization for System FC, with Dimitrios Vytiniotis, describes how GHC optimses big coersions into little ones.  This turns out to be extremely important in practice; without the optimisation GHC can choke on type-function-rich programs.
  • [July 2013] Exploiting vector instructions with generalised stream fusion describes how Geoff made stream fusion work so well that we can write numerically intensive Haskell programs that run faster than their C equivalents. ICFP'13.
  • [Sept 2012] Bringing Computer Science Back Into Schools: Lessons from the UK, with Neil Brown, Michael Kolling, Tom Crick, Simon Humphreys, and Sue Sentance.  This paper tells the still-developing story of the UK's Computing at School Working Group.
  • [July 2012] Vectorisation avoidance, with Gabriele Keller, Manuel Chakravarty, Roman Leshchinskiy, Ben Lippmeier, Haskell Symposium 2012.  Describes a major improvement to the "vectorisation transformation" in Data Parallel Haskell.
  • [July 2012] Safe Haskell, with David Terei, David Mazieres, and Simon Marlow, describes how to make Haskell safe enough to confine and safely execute untrusted, possibly malicious code.
  • [July 2012] HALO: Haskell to Logic through Denotational Semantics, with Dimitrios Vytiniotis, Koen Claessen, and Dan Rosen.  Describes how to translate Haskell and user-specified contract specifications into first order logic, and thereby prove that the program satisfies the contract.
  • [July 2012] Guiding parallel array fusion with index types, with Ben Lippmeier, Manuel Chakravarty, and Gabriele Keller, Haskell Symposium 2012.  This paper describes the Repa 3 array library, using indexed type families to control the data representation.
  • [May 2012] The Glasgow Haskell Compiler, in The Architecture of Open Source Applications, Volume II, ed Brown & Wilson. This paper gives an up to date (2012) technical overview of GHC.
  • [March 2012] Equality proofs and deferred type errors, with Dimitrios Vytiniotis and Pedro Magalhaes (ICFP12).  An exploration of what happens when you take equality proofs seriously in a compiler.  (A predecessor was our unpublished paper Practical aspects of evidence-based compilation in System FC, still available on the same URL as above.)
  • [March 2012] Work-efficient higher-order vectorisation, with Ben Lippmeir, Gabriele Keller, Manuel Chakravarty, and Roman Leshchinskiy (ICFP12).  It turns out that a naive application of the "vectorisation transformation" in Data Parallel Haskell can be asymptotically less efficient than the original program.  Bad news!  This paper describes how to fix the problem. 
  • [Dec 2011] Closer to Nirvana a Channel 9 interview with Charles Torre.
  • [October 2011] Giving Haskell a promotion (with Brent Yorgey, Stepanie Weirich, Julien Cretin, and Dimitrios Vytiniotis).  How to (a) add kind polymorphism and (b) promote data types to become data kinds.  TLDI 2012.
  • [July 2011] Termination combinators forever (with Max Bolingbroke and Dimitrios Vytiniotis) describes a nice modular combinator library for doing online termination checking.  Very useful in a supercompiler, but with other applications too. Haskell Symposium, Tokyo, Sept 2011.
  • [June 2011] Multicore garbage collection with local heaps (principal author Simon Marlow), International Symposium on Memory Management, June 2011.
  • [May 2011] Parallel and concurrent programming in Haskell.  Simon Marlow's 70-page Summer School tutorial.
  • [April 2011 (JFP final)] Modular type inference with local assumptions (with Dimitrios Vytiniotis, Tom Schrijvers, Martin Suzmann).  This epic 83-page JFP paper brings together, in a single uniform framework, a series of our earlier papers on type inference for type systems involving local constraints, including GADTs and indexed type families.  This is the camera ready copy for JFP.
  • [Mar 2011] Improving supercompilation: tag-bags, rollback, speculation, normalisation, and generalisation, with Max Bolingbroke. Max is on a roll; this paper describes the progress we have made in supercompilation since last year's Haskell Symposium paper.  Rejected by ICFP'11.
  • [Mar 2011] Efficient Parallel Stencil Convolution in Haskell, with Ben Lippmeier, Gabriele Keller. This paper desribes (mainly) Ben's adventures in applying Repa to a practical problem. New stuff includes a multi-region, cursored representation for arrays. Haskell Symposium 2011.
  • [June 2011] Towards Haskell in the cloud, with Jeff Epstein and Andrew Black.  Imitation is the sincerest form of flattery, and this paper does homage to Erlang. We try to combine Erlang's best ideas with Haskell strong typing. On the way we describe a neat new approach to giving programmers control over serialisation for function closures. Haskell Symposium, Tokyo, Sept 2011.
  • [June 2011] A monad for deterministic parallelism, with Simon Marlow and Ryan Newton.  Using par/seq to write parallel Haskell programs can be frustrating; this paper explains why and offers a possible solution.  Haskell Symposium, Tokyo, Sept 2011.
  • [Mar 2011] Parallel = functional: the way of the future: slides (7Mbyte PDF), video.  A keynote talk at the London FP Exchange (18 March 2011), giving a whirlwind overview of what's going on in the world of parallel Haskell. 
  • [July 2010] Generative Type Abstraction and Type-level Computation (with Stephanie Weirich, Dimitrios Vytiniotis, and Steve Zdancewic).  This paper, which appeared in POPL'11, describes how to combine Haskell's new abilities to do type-level computation with the old ability to do type abstraction using newtypes.  Rather surprisingly (to me) the two are in tension, and the solution is quite interesting.
  • [June 2010] Seq no more (by Simon Marlow, Patrick Maier, Phil Trinder, Hans-Wolfgang Loidl, and Mustafa Aswad).  A new take on the "algorithms + strategies = parallelism" story, providing a nice Haskell library to support parallel computation.  Haskell Symposium 2010 .
  • [June 2010] Supercompilation by evaluation (with Max Bolingbroke).  This is our first foray into supercompilation.  To appear at the 2010 Haskell Symposium.
  • [June 2010] The performance of Haskell 'containers' package (by Milan Straka).  Milan did this work while an intern here at MSR Cambridge.  Haskell Symposium 2010.
  • [April 2010] Hoopl: A Modular, Reusable Library for Dataflow Analysis and Transformation (with John Dias and Norman Ramsey). This paper, completely rewritten in April 2010, describes our framework for doing dataflow optimisation on imperative C-- programs. Haskell Symposium 2010.
  • [April 2010] Regular, shape-polymorphic, parallel arrays in Haskell (with Manuel Chakravarty, Gabriele Keller, Roman Leshchinskiy, and Ben Lippmeier) describes a high-performance data-parallel library for regular arrays. To appear at ICFP 2010.
  • [Oct 2009] Let should not be generalised, with Dimitrios Vytiniotis and Tom Schrijvers. This paper argues that local let-bindings should not be generalised: although taken for granted, it is a feature that is seldom used, and it greatly with recent type-system developments, such as GADTs and type functions. Appeared at TLDI 2010.
  • [May 2009] Types are calling conventions (with Max Bolingbroke), and its discussion page. Describes an intermediate language that supports much more precise calling conventions than GHC's current Core language. Haskell Symposium 2009.
• About Haskell generally
  • Interviews: It's raining Haskell (with John Hughes, Channel 9, Dec 2011, http://channel9.msdn.com/Blogs/Charles/YOW-2011-Simon-Peyton-Jones-and-John-Hughes-Its-Raining-Haskell); Closer to Nirvana (Channel 9, Dec 2011), InfoQ (Aug 2009), with Joe Armstrong; ComputerWorld (Sept 2008, magazine article); QCon interview (March 2008); Port 25 at OSCON (July 2007, 25 mins video); Channel 9, Haskell and Nirvana (June 2007, 5 mins, video); Software Engineering Radio (Spring 2007, sound).
  • [July 2009] Classes, Jim, but not as we know them. My invited talk for ECOOP 2009 discusses the relationship between Haskell's type classes and object-oriented programming. Channel 9 video of the talk. Here's Joe Duffy's interesting blog post discussing the issues raised in the talk.
  • [June 2009] Haskell and Erlang: growing up together. An invited talk for the Erlang Factory meeting in June 2009. Here's the video of the talk. And video of an InfoQ interview with Joe Armstrong and myself.
  • [2008] Caging the effects monster: the next big challenge. These slides (8Mbytes) are from a talk I gave at QCon'08 and ACCU'08, suggesting that a big programming-language theme over the next ten years will be mechanisms to restrict or control unrestricted side effects. Haskell's monads are one approach, but it is not the only one. One way or another, though, we need to get a handle on those effects.
  • [July 2007] A taste of Haskell. I had the chance to deliver this three-hour tutorial about Haskell at the O'Reilly Open Source Convention in Portland, 2007. There's a video too.
  • [June 2007] Comprehensive comprehensions: comprehensions with "Order by" and "Group by", Phil Wadler and Simon Peyton Jones, submitted to Haskell Workshop 2007. We explore some generalisations of list comprehensions that give them the power of the SQL GROUP BY and ORDER BY constructs.
  • [Jan 2007] A History of Haskell: being lazy with class. Paul Hudak (Yale University), John Hughes (Chalmers University), Simon Peyton Jones (Microsoft Research), Philip Wadler (Edinburgh University), The Third ACM SIGPLAN History of Programming Languages Conference (HOPL-III) San Diego, California, June 9-10, 2007. This long (55-page) paper describes the history of Haskell, including its genesis and principles, technical contributions, implementations and tools, and applications and impact.
• Compiler stuff
  • [April 2007] Constructor specialisation for Haskell programs, Simon Peyton Jones. An in-depth description of a new optimising transformation in GHC.
  • [April 2007] Faster laziness using dynamic pointer tagging, Simon Marlow, Alexey Rodriguez Yakushev, and Simon Peyton Jones. How to squeeze another 10-15% performance out of GHC by tagging pointers.
• Papers about parallelism in Haskell
  • [March 2009] Runtime Support for Multicore Haskell (with Simon Marlow and Satnam Singh), ICFP'09. An overview of GHC's parallel runtime, lots of optimisations, and lots of measurements.
  • [Oct 2008] A Tutorial on Parallel and Concurrent Programming in Haskell (with Satnam Singh), Advanced Functional Progamming Summer School, Nijmegen, May 2008, LNCS (to appear).
  • [Oct 2008] Harnessing the Multicores: Nested Data Parallelism in Haskell (with Gabriele Keller, Roman Leshchinskiy, and Manuel Chakravarty), FSTTCS 2008. This paper describes the Barnes-Hut algorithm in Data Parallel Haskell, and gives a detailed tutorial of the vectorisation transformation.  The same link gets you to slides and video of a talk about the paper.
  • [April 2008] Parallel generational-copying garbage collection with a block-structured heap (with Simon Marlow, Roshan James, Tim Harris).
  • [Jan 2008] Partial vectorisation of Haskell programs, (with Manuel Chakravarty, Roman Leshchinskiy, Gabriele Keller), DAMP'08.
  • [June 2007] Lightweight concurrency primitives for GHC, Peng Li, Andrew Tolmach, Simon Marlow, and Simon Peyton Jones; submitted to Haskell Workshop 2007. In this paper we try to re-factor GHC's large and complex run-time system, so that much of it becomes a vanilla Haskell library, with much less of it written in C.
  • [Nov 2006] Data Parallel Haskell: a status report (with Manuel Chakravarty, Roman Leshchinskiy, Simon Marlow, and Gabriele Keller). This short paper gives an overview of our work to extend Haskell with data parallelism. Here is the home page for our Data Parallel Haskell project.
  • [Apr 2007] Feedback directed implicit parallelism by Tim Harris and Satnam Singh. A limit study of implicit parallelism in Haskell, and a feedback-directed mechanism to increase its granularity.
  • [July 2005] Haskell on a Shared-Memory Multiprocessor (with Simon Marlow and Tim Harris), Haskell workshop 2005. We can now run GHC in parallel on a shared-memory multiprocessor.
• Papers about Software Transactional Memory, (with Tim Harris, Maurice Herlihy, and Simon Marlow). This series of papers about transactional memory in Haskell, describes a new coordination mechanism for concurrent programs.
  • [July 2007] Slides and video from a short 15-minute keynote at OSCON 2007 on STM
  • [Jan 2007] Beautiful concurrency (a tutorial in the O'Reilly book "Beautiful code")
  • [June 2006] Transactional memory with data invariants (FLOPS'06)
  • [Apr 2006] Lock-free data structures using STMs in Haskell (FLOPS'06)
  • [June 2005] Composable memory transactions (PPOPP'05, typos fixed, appendix added)
  • [2006] Channel 9 interview
• Papers about types
  • [May 2009] Fun with type functions (with Ken Shan, and Oleg Kiselyov). A tutorial on indexed type families, and associated types in Haskell. Channel 9 video of the talk: http://channel9.msdn.com/posts/MDCC-TechTalk-Fun-with-type-functions
  • [March 2009] Complete and Decidable Type Inference for GADTs (with Tom Schrijvers, Martin Sulzmann, and Dimitrios Vytiniotis), ICFP'09. Yes, it's another a stab at type inference for GADTs, but I think a great improvement on our previous attempt.
  • [April 2008] FPH : First-class Polymorphism for Haskell ( with Dimitrios Vytiniotis and Stephanie Weirich), submitted to ICFP 2008. This is a completely new paper, much better than our old "boxy type" paper (although you'll still see boxes in it).
  • [April 2008] Type Checking with Open Type Functions, (with Tom Schrijvers, Manuel Chakravarty, Martin Sulzmann), submitted to ICFP'08. This is a much more thorough look at the challenge of type checking in the presence of open type functions.
  • [April 2007] Scrap your type applications, Barry Jay and Simon Peyton Jones. Have you ever thought that the type applications in System F are verbose and often redundant? Here's a possible way to get rid of (most of) them.
  • [Sept 2007] Towards open type functions for Haskell, Tom Schrijvers, Martin Sulzmann, Simon Peyton Jones, and Manuel Chakravarty, submitted to the Implementing Functional Languages workshop, Sept 2007 (IFL07).
  • [Apr 2006] System F with Type Equality Coercions (with Martin Sulzmann and Manuel Chakravarty). This paper describes System FC, a modest extension to System F that can accommodate GADTs, associated types, and functional dependencies. GHC now uses FC as its intermediate language. (Rejected by ICFP'06; revised; rejected by POPL'07; revised again; submitted to TLDI'07.)
  • [Revised (again) April 2006] Simple unification-based type inference for GADTs (with Dimitrios Vytiniotis, Stephanie Weirich, and Geoffrey Washburn), ICFP'06. This is a completely-rewitten and much-simplified verison of our orignal "wobbly-type" paper. It has been rewritten from beginning to end so, if you liked the earlier paper, this one is probably worth reading too. The big recent change is the idea of a "fresh most general unifier".
  • [Revised April 2006] Boxy types: type inference for higher-rank types and impredicativity (with Dimitrios Vytiniotis and Stephanie Weirich); ICFP'06. It is also now fully implemented in GHC.
  • [Revised Feb 2006] Understanding functional dependencies via Constraint Handling Rules, Martin Sulzmann, Gregory J. Duck, Simon Peyton Jones, and Peter J. Stuckey. To appear in the Journal of Functional Programming.
  • [Revised Feb 2006] Practical type inference for arbitrary-rank types (with Stephanie Weirich, Dimitrios Vytiniotis, Mark Shields), to appear in the Journal of Functional Programming. Long in gestatation, the paper describes the approach that GHC takes to type inference for higher-rank types. It has a strongly tutorial flavour, and comes with an executable implementation.
  • [April 2005] Associated type synonyms (with Manuel Chakravarty and Gabrielle Keller). Our earlier paper discussed allowing data type declarations in type-class signatures. This follow-up (submitted to ICFP'05) suggests allowing type synonyms too.
• Static verification of Haskell programs
  • [July 2008]Static contract checking for Haskell, (with Dana Xu and Koen Claessen), submitted to POPL 2009. This paper describes progress on static verification of Haskell programs.
• Other papers
  • [May 2009] Finding the needle: stack traces for GHC (with Tristan Allwood and Sue Eisenbach). Lightweight debugging support for lazy functional programs. Haskell Symposium 2009.
  • [Jan 2006] Haskell is not not ML (ESOP'06; main credit to Ben Rudiak-Gould and Alan Mycroft) describes a CPS-based intermediate language that can serve as a target for both call-by-name and call-by-value.
  • [July 2005] A monadic framework for delimited continuations (with Kent Dybvig and Amr Sabry, JFP 17(6) Nov 2007, pp 687-730). This foray into continuations, arising from Amr's sabbatical visit in 2004, gives a monadic way of understanding delimited continuations. You can download an implementation of the approach in the paper, written by Dan Doel.
  • [April 2005] Scrap your boilerplate with class: extensible generic functions (with Ralf Laemmel). The third paper in the "scrap your boilerplate" series; this one shows how to write open or extensible generic functions, something we previously thought was impossible.
  • [Jan 2005] The full text of my out-of-print 1987 book The implementation of functional programming languages is now available online, thanks to the heroic efforts of Marnie Montgomery.
  • [March 2004] Lexically scoped type variables, (with Mark Shields). Rejected by ICFP 2004.
  • [March 2004] Champagne Prototyping: A Research Technique for Early Evaluation of Complex End-User Programming Systems, with Margaret Burnett and Alan Blackwell. VL/HCC'04. This is a follow on to our earlier paper "A user-centred approach to functions in Excel".
  • [Nov 2000] Featherweight concurrency in a portable assembly language.

Haskell stuff

• The International Conference on Functional Programming.
• The Revised Haskell 98 Report, at last completed.
• The main Haskell home page
• The Glasgow Haskell Compiler
• Johan Tibell's State of Haskell 2010 questionnaire results
• John Hughes's links to tutorials on functional programming.
• A History of Haskell: being lazy with class.
• Tackling the awkward squad: monadic input/output, concurrency, exceptions, and foreign-language calls in Haskell.
• Type classes: exploring the design space
• Wearing the hair shirt: a retrospective on Haskell. Slides of my invited talk at POPL'03.
• A taste of Haskell. Video and slides fro my tutorial on Haskell at the O'Reilly Open Source Convention in Portland, 2007.
• A complete archive of the Haskell mailing list (a single gzipped file) from 11 Sept 1990 to 27 Oct 2000. From Nov 200 all the mail is archived at the main Haskell mailing list.

Who I am and what I do

I'm a researcher at Microsoft Research in Cambridge, England. I started here in Sept 1998. I'm also an Honorary Professor of the Computing Science Department at Glasgow University, where I was a professor during 1990-1998.

I am married to Dorothy, a priest in the Church of England. We have six children (three adopted).

I'm interested in the design, implementation, and application of lazy functional languages. In practical terms, that means I spend a most of my time on the design and implementation of the language Haskell. In particular, much of my work is focused around the Glasgow Haskell Compiler, and its ramifications.

Microsoft Research is next door to the Cambridge University Computer Lab, and I co-supervise a number of PhD students at the Computer Lab. If you are interested in doing a PhD at Cambridge in my area, then I am very happy to discuss it with you.

Here is

• A brief biography, suitable for seminar announcements and suchlike.
• A collection of pictures of me, at various resolutions.
• A 2014 profile by MSR
• Muffy Calder's oration at my 2013 honorary DSc ceremony
• For amusement, a collection of pictures of me having fun, taken by John Petersen in 2008.

Social networks

I use LinkedIn for professional networking, but I restrict my connections to people who I know personally, or with whom I have had some meaningful two-way professional interaction; that is, not simply people with whom I share a professional interest.

I use Facebook for non-work networking, but only for people who my family knows too.

I do have a Twitter account, for some reason, but I have yet to find something significant enough to say that it's worth tweeting.

In all three cases my actual use is minimal, so don't hold your breath.

Email: simonpj@microsoft.com
Phone: +44 1223 479 848 (direct)
Fax: +44 1223 479 999
WWW: http://research.microsoft.com/~simonpj/

Directions for how to get to MSR Cambridge