Simon Peyton Jones

Lead designer of the Glasgow Haskell Compiler, Principal researcher at Microsoft Research

Simon Peyton Jones, FRS, spent seven years as a lecturer at University College London, and nine years as a professor at Glasgow University, before joining Microsoft Research (Cambridge) in 1998. He moved to Epic Games as an Engineering Fellow in 2022.

Simon’s main research interest is in functional programming languages, their implementation, and their application. He was a key contributor to the design of the now-standard functional language Haskell, and is the lead designer of the widely-used Glasgow Haskell Compiler (GHC). He has written two textbooks about the implementation of functional languages. He is particularly motivated by direct application of principled theory to practical language design and implementation — that is one reason he loves functional programming so much.

Simon is chair of Computing at School, the grass-roots organisation that was at the epicentre of the 2014 reform of the English computing curriculum.

The world’s most widely used programming language is a purely functional language! It’s called Excel. No mutable cells, assignment statements, or sequencing; just pure functions and immutable values. But, despite its phenomenal success, considered as a functional programming language, Excel’s formulas constitute a very limited language: it is largely restricted to scalar values, and you can’t write new user-defined functions.   Until now. Excel has just released LAMBDA, in its full higher-order glory, just as Alonzo Church defined it in the 1930s. That’s pretty exciting, because now you can define new functions, which can call other lambda-defined functions, to arbitrary depth, and even recursively. It represents a qualitative change not an incremental one: Excel just became Turing-complete.   In this talk we’ll tell you some things you may not know about Excel’s existing formula language, we’ll describe the journey that led a few geeks at Microsoft Research Cambridge to influence one of the most widely used programs in history, and we’ll show you some other ideas we’ve been playing around with.   Lambda Days indeed!

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