Last update: 28th September 2014

Papers, Teaching, Media, Biography, Contact, Links

Laurence E. Day

I'm a few-weeks-shy-of-no-longer-being-one research PhD student in the Functional Programming Laboratory of the School of Computer Science at the University of Nottingham, supervised by Professor Graham Hutton. I'm predominantly a Haskell programmer, but also meddle with Standard ML, OCaml, Clojure and Python.

My current research concerns investigating the possibilities of using monads as an aid to constructing modular compilers within a functional framework, building upon previous work in the field on modular interpreters. I'm also interested in methods of proving program correctness, category theory, automated theorem proving within functional languages and computational complexity theory.

I'm in the arduous process of writing up my thesis, entitled `The Modular Compilation of Effects'. A thesisometer detailing its progress is available here. Put more succinctly, check for the single bit of information you're looking for.

In Q4 2013, I worked at Intel Labs in Hillsboro, Oregon as part of the Programming Systems Lab on the Haskell Research Compiler. The paper describing the work I undertook is given below, having appeared at FHPC 2014.

I've also recently become involved in the hacking community. I was one-quarter of the winning team at Hackference 2.0.14 in Birmingham, presenting a Rube Goldberg machine constructed via multiple languages, platforms and APIs. I'm also part of the Ground Control team for Major League Hacking UK, as well as a member of Hacksoc Nottingham.


Native Offload of Haskell Repa Programs to Integrated GPUs (with Hai Liu, Neal Glew, Todd A. Anderson and Rajkishore Barik, FHPC 2014)

In light of recent hardware advances, General Purpose Graphics Processing Units (GPGPUs) are becoming increasingly commonplace, and demand novel programming models to account for their radically different architecture. For the most part, existing approaches to programming GPGPUs within a high-level programming language choose to embed a domain specific language (DSL) within a host metalanguage and implement a compiler mapping programs written within said DSL to code in low-level languages such as OpenCL and CUDA. We question this design choice, and argue that by directly implementing a GPGPU offload primitive as part of a general-purpose language compiler, we gain access to a substantial number of existing optimisations without having to reimplement them in a DSL compiler. In this paper we describe the structure of our prototypical treatment of this research direction, demonstrating the applicability of our approach by showing how to bridge between APIs by extending the Repa library of Haskell with an offload primitive, and detailing an experimental implementation of our approach within the Intel Labs Haskell Research Compiler (HRC). We also provide a detailed study of a set of nine benchmarks, by compiling them to both GPU and two distinct CPUs and comparing their performance.

Pick'n'Fix: Capturing Control Flow in Modular Compilers (with Patrick Bahr, TFP 2014)

We present a modular framework for implementing languages with effects and control structures such as loops and conditionals. This framework enables modular definitions of both syntax and semantics as well as modular implementations of compilers and virtual machines. In order to compile control structures, in particular cyclic ones, we employ Oliveira and Cook's purely functional representation of graphs. Moreover, to separate control flow features semantically from other language features, we represent source languages using Johann and Ghani's encoding of generalised algebraic datatypes as fixpoints of higher-order functors. We demonstrate the usage of our modular compiler framework with two running examples and highlight the extensibility of our modular semantic definitions and compiler implementations.

Compilation À La Carte (with Graham Hutton, IFL 2013)

In previous work, we proposed a new approach to the problem of implementing compilers in a modular manner, by combining earlier work on the development of modular interpreters using monad transformers with the a la carte approach to modular syntax. In this article, we refine and extend our existing framework in a number of directions. In particular, we show how generalised algebraic datatypes can be used to support a more modular approach to typing individual language features, we increase the expressive power of the framework by considering mutable state, variable binding, and the issue of noncommutative effects, and we show how the Zinc Abstract Machine can be adapted to provide a modular universal target machine for our modular interpreters.

Programming Macro Tree Transducers (with Patrick Bahr, WGP 2013)

Tree transducers are tree automata defining functions from trees to trees. Put simply, a tree transducer is a set of mutually recursive functions transforming an input tree into an output tree. Macro tree transducers extend this recursion scheme by allowing each function to be defined in terms of an arbitrary number of accumulation parameters. In this paper, we show how macro tree transducers can be concisely represented in Haskell, and demonstrate the benefits of using such an approach with a number of examples. In particular, tree transducers afford a modular programming style as thy can be easily composed and manipulated. Our Haskell representation generalises the original definition of (macro) tree transducers, abolishing a restriction on finite state spaces. However, as we demonstrate, this generalisation does not affect compositionality.

Towards Modular Compilers For Effects (with Graham Hutton, TFP 2011) [winner: Best Paper Award]

Compilers are traditionally factorised into a number of separate phases, such as parsing, type checking, code generation, etc. However, there is another potential factorisation that has received comparatively little attention: the treatment of separate language features, such as mutable state, input/output, exceptions, concurrency, etc. In this article we focus on the problem of modular compilation, where the aim is to develop compilers for separate language features and prove their correctness independently, which can then be combined as required. We summarise our progress so far, issues that have arisen, and further work.


As of January 2014, I stopped tutoring any undergraduate modules, as I am now primarily based in Leeds for the purposes of writing my thesis (that and winning the Staff Oscar for Best Postgraduate That Teaches in 2013 meant I wanted to leave on a high!). However, a failure to be anywhere in person has never stopped me before! If you have a question related to any of the below modules, I am more than happy to respond to emails or Facebook messages, provided you aren't asking me as a last ditch effort for a piece of coursework or revision!

Teaching Assistant

Spring Semester

G51FUN Functional Programming ['12-'13] ['11-'12] ['10-'11], ['09-'10]

G52AFP Advanced Functional Programming ['12-'13] ['11-'12] ['10-11]

G52MAL Machines and their Languages ['12-'13] ['11-'12] ['10-'11]

Autumn Semester

G51MCS Mathematics for Computer Scientists ['12-'13] ['11-'12] ['10-'11]

G51APS Algorithmic Problem Solving ['12-'13] ['11-'12]

G53CMP Compilers ['12-'13] ['11-'12]


No stranger to ridicule, I filmed an instructional video for the Computerphile project in August 2013 contrasting Java and Haskell. My silly delimiter error aside, you can view said video here:

In Q4 2014 I will be filming a series of videos for Computerphile on the topic of cryptocurrencies, in particular the rise and usage of Bitcoin. Stay tuned!


IRL: Office A04, Functional Programming Laboratory, School of Computer Science, Jubilee Campus, Nottingham NG8 1BB

Facebook: Laurence E. Day - I keep this account public to all, but opinions are obviously my own, and nobody should take anything depicted there as fact.

Email: led at cs dot nott dot ac dot uk [soon to default to dizzeehaskell at gmail dot com]

Twitter: @dizzeehaskell


Functional Programming Laboratory

School of Computer Science, University of Nottingham

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