Jamie Willis

Teaching Fellow

Huxley 306
Department of Computing
Imperial College London

About Me

I am a Teaching Fellow in the Department of Computing at Imperial where I coordinate the Second-Year of the UG programme. My interests include functional programming, parsing, and compiler writing. I predominantly program in Scala and Haskell, though mostly the former these days.

Teaching

I am involved in both lab support and lecturing at Imperial.

Modules

• COMP40009 Computing Practical 1
  I taught the first 6 weeks of the course in Haskell in 2024 covering for Nicolas Wu, who was on sabbatical. This is an introduction to functional programming, including polymorphism, lists, higher-order functions, functors, applicatives, monads, and containers. Since Autumn 2025, I teach the practical side of the course, managing the weekly exercises and teaching practical concepts such as containers, applicative parsing, and benchmarking performance. From 2025, I started writing the yearly Haskell interim and final tests, taking over from Tony Field.
  Autumn 2024–present
• COMP50001 Algorithm Design and Analysis
  I covered this course for Nicolas Wu, who was on sabbatical. This is an interesting take on an algorithms course, taught in Haskell, focusing on building algorithmic thinking using persistent, structural-sharing, data structures as a motivating backdrop. The course also discusses amortized complexity analysis and algorithm design via numerical systems culminating in a linear-time building for Red-Black Trees based on strange new counting system.
  Autumn 2024
• COMP50006 Compilers
  I took over the first half of the old compilers course, covering parsing and semantic analysis. I modernised the content, removing detailed discussion of LL and LR parsing strategies and instead focused on scannerless PEG parsing. I introduced renamers and taught top-down typechecking via a constraints-like system. While the course was taught for the last time in the second-year that year, the module will be reworked both as an advanced third-year module as well as a new compilers crash course: COMP50007.2 Introduction to Compilers.
  Spring 2025
• COMP50007 Computing Practical 2
  Since Spring 2020 I've been a part of CP2, involved in both the Autumn term PintOS Operating Systems project (which is really a concurrency project in disguise) and the Spring term WACC compilers project (which is really a software engineering project in disguise). I have ran the WACC project since Spring 2023, and became the module lead in Autumn 2023.
  Autumn+Spring 2023-present
• COMP50010 Designing for Real People
  Co-taught with the Royal College of Arts, this module exposes students to Human-Centered Design, getting them to develop an interactive app or website that connects people, solving a real problem in a way that really supports the people its designed for. It's a really fun and interesting module, which is quite different to anything else the students are exposed to at Imperial!
  Summer 2024-present

Programming Tests

Open-Source Contribution

I enjoy doing open-source work for both the Scala and Haskell communities, including the following libraries:

• parsley (owner): a modern parser combinator library for Scala; evolution of my Master's thesis.
• gigaparsec (owner): a reimagining of the parsley API in Haskell.
• parsley-cats (owner): cats support for parsley.
• dill (owner): interactive debugger for parsley. Developed as part of a Software Engineering Group Project at Imperial written with a Rust backend and Scala frontend.
• sbt-typelevel (maintainer): SBT plugin to remove boilerplate from configuration of Scala libraries.

I also maintain sites and tools here at Imperial. Some of the more public efforts are:

• WACC Reference Compiler: web frontend for the (private) reference compiler implementation for the second-year WACC compilers project, live here. It is implemented in pure Scala, using Scala.js and Laminar on the frontend and Scala on the backend.

Publications

• Parsley: Optimising and Improving Parser Combinators
  Jamie Willis. PhD Thesis, Department of Computing, Imperial College London, 2024. https://doi.org/10.25560/110313
• Design Patterns for Parser Combinators in Scala
  Jamie Willis & Nicolas Wu. Proceedings of the 13th ACM SIGPLAN Scala Symposium, 2022. https://doi.org/10.1145/3550198.3550427
• Oregano: Staging Regular Expressions with Moore Cayley Fusion
  Jamie Willis, Nicolas Wu & Tom Schrijvers. Proceedings of the 15th ACM SIGPLAN International Symposium on Haskell (Haskell ’22), 2022. https://doi.org/10.1145/3546189.3549916
• Design Patterns for Parser Combinators
  Jamie Willis & Nicolas Wu. Proceedings of the 14th ACM SIGPLAN International Symposium on Haskell (Haskell ’21), 2021. https://doi.org/10.1145/3471874.3472984
• Staged Selective Parser Combinators
  Jamie Willis, Nicolas Wu & Matthew Pickering. Proceedings of the ACM on Programming Languages (ICFP), 2020. https://doi.org/10.1145/3409002
• Garnishing Parsec with Parsley
  Jamie Willis & Nicolas Wu. Proceedings of the 9th ACM SIGPLAN International Symposium on Scala (Scala ’18), 2018. https://doi.org/10.1145/3241653.3241656

Last updated: Dec '25