School of Informatics

Informatics Researchers recognised for a historic paper on effect handlers

Ohad Kammar, Sam Lindley and Nicolas Oury were awarded the Most Influential ICFP Paper Award, which is presented annually to the authors of a paper presented at the International Conference on Functional Programming held 10 years prior to the award year. Informatics researchers and a former Informatics PDRA Nicolas Oury, received the recognition for their 2013 paper ‘Handlers in action’.

International Conference on Functional Programming

The findings described in the paper developed the theory of the effect handler construct that had been pioneered by Gordon Plotkin and Matija Pretnar.  

Kammar, Lindley and Oury set out to popularise the handler abstraction with their paper: it includes an introduction to its use, a collection of illustrative examples, and a straightforward operational semantics.

This paper drew the attention of the ICFP community to handlers as an abstraction for effectful computation. In exposition, and in providing the first operational semantics for handlers & effects, and an effect system, it seeded many subsequent works. Pragmatically, it detailed implementation of handlers in Haskell, and outlined the ideas behind OCaml, SML, and Racket implementations, as well as providing experimental results comparing handlers with equivalent monadic code.

The award citation

Ohad Kammar reflects that the collaborative and interactive research culture and traditions at the School and the LFCS fostered and encouraged the authors to develop this work.A SICSA-funded PhD student at the time, the School funded his attendance to an inspirational Domain Theory workshop in Swansea, and Pretnar’s seminar LFCS seminar: both contributed to his interest in the topic of effect handlers and forming the collaboration with Lindley and Oury, both then PDRAs in the School.  

An impact case study on effect handlers was included in the School of Informatics and EPCC’s 2021 REF submission, which received 100% top grades for impact. The case study describes how handlers were used industrially and at scale in the Open Source platform GitHub, for statistical modelling at Uber, and for web programming at Meta. It evidences that the functional programming paradigm, which we teach our first-year undergraduate cohort in their Introduction to Computation in this time of year, serves as a hotbed for advanced programming abstractions that later spread and impact millions of programmers and billions of users world-wide every day.Gordon Plotkin and Matija Pretnar were recognised for their 2009 paper Handlers of Algebraic Effects which with the Test of Time Award at the ETAPS conference in 2022. 

Previous award holders include Prof. Stephanie Weirich who gave the Milner Lecture last year, and Prof. Peter Sewell who will give the Milner Lecture later this year as part of the 60 years of Computer Science celebrations. 

ICFP'23 Grand Ballroom 2 - Speech by Sam Lindley

Related links

Link to full paper

Link to previous news item on 'Informatics researchers awarded for their seminal work on effect handlers'

Link to Informatics 2021 REF results

Examples of Informatics impact case studies