Léonard Oest O'Leary

About

For the past five years, I have been building compilers and programming languages in both research and industry settings. I was hired at Meta (Facebook), developed my own compiler, Ribbit, as part of my master’s degree, contributed to LLVM, and published at renowned conferences such as ISMM, where our paper received a Best Paper Award.

Currently, I’m working on Ribbit with support from an NLnet grant. Ribbit is a Scheme compiler that uses a unique compilation technique called Virtual Machine Tailoring developed as part of my master’s research. The goal of the grant is to bring Ribbit to more people by adding Scheme (R7RS) and Lua support as source languages.

I started my academic journey before university, publishing research papers during Cégep with Jihene Rezgui, Ph.D. Upon entering university, I worked with Prof. Marc Feeley who sparked my interest in functional languages and their implementations. I was fortunate enough to be surrounded by exceptional mentors such as Prof. Stefan Monnier and Prof. Ian Arawjo during my bachelor’s and master’s studies.

Research interests

Here is a non-exhaustive list of my research interests grounded in previous experience:

• Meta-compilation: I love to think about the compiler as a program that can be extended and even generated. This can take different forms, from Lispy macros to meta-compilers generating parts or entire compilers. During my master’s studies, I explored a new compilation technique called Virtual Machine Tailoring, which generates a specialized interpreter given a source program. I’m amazed by the power this approach provides.

• Optimization for constrained environments: Many compiler optimizations aim to increase the execution speed of programs. However, some environments might not be able to benefit from these optimizations because of memory or power constraints. Furthermore, programs may be subject to other requirements, such as strict timing or low latency, which demand novel optimizations. I have designed optimizations for memory-constrained environments and co-designed a garbage collector algorithm when synchronous and immediate collection of objects is required.

• Designing better interfaces for programmers: While working, programmers use interfaces to communicate their intent to computers. These interfaces can take the form of a programming language, a debugger, a code editor or more recently a coding agent. I’m interested in ways to design these interfaces to improve the productivity of programmers. For example, I led a user-study with 18 participants on the impact of back-stepping while debugging and experimented with reactive programming in Scheme to ease the development of Web applications.

In my free time, you can find me climbing, competing in water polo tournaments, dancing Lindy Hop (swing) and playing piano. Also, look at these games that I made. I also built this DuckieBot that I taught to drive!

You can reach me by email at: leonard <at> oestoleary <dot> com, by replacing the <dot> with a . and the <at> with an @. Don’t hesitate to send me an email, even just to say hi!

You can also find me on GitHub, LinkedIn, orcid and Google Scholar.

I have been a teaching assistant for the following courses at the Université de Montréal during my bachelor’s and master’s studies:

• Programming Languages and Compiling (IFT3065/IFT6232) - Winter 2023, Winter 2025, Fall 2026.
• Introduction to programming (IFT1015) - Fall 2020, Fall 2021, Winter 2022.
• Introduction to programming for Neuroscience (IFT1016) - Fall 2019, Fall 2020.

I have also been president of AÉDIROUM, the student association of the Department of Computer Science and Operations Research (DIRO) at the Université de Montréal. I was elected to serve during the 2021–2022 term.

• NLnet through NGI0 Commons Fund. Ribbit: An Portable Platform for Language Interoperability.
• Best Paper Award @ ISMM25 (International Symposium on Memory Management). This was awarded for Arborescent Garbage Collection: A Dynamic Graph Approach to Immediate Cycle Collection.
• Natural Sciences and Engineering Research Council (NSERC), Canada Graduate Scholarship, Master’s.
• Fonds de recherche du Québec Nature et technologies (FRQNT), Bourses de formation à la maîtrise.
• Natural Sciences and Engineering Research Council (NSERC), Undergraduate Student Research Awards. Awarded twice.
• Fonds de recherche du Québec Nature et technologies (FRQNT), Suppléments aux bourses de 1er cycle. Awarded twice.
• Université de Montréal, Bachelor’s entry scholarship.