Annual Peter Landin Semantics Seminar: Compiling without continuations

When: 12th Dec 2017, 18:00 - 12th Dec 2017, 21:00
Where: BCS, 1st Floor, The Davidson Building, 5 Southampton Street, London, WC2E 7HA
Town/City: London
Organiser: BCS FACS (Formal Aspects of Computing Science) Group
Price: Free of charge
Further Information: Further Information

Peter Landin (1930 - 2009) was a pioneer whose ideas underpin modern computing. In the 1950s and 1960s, Landin showed that programs could be defined in terms of mathematical functions, translated into functional expressions in the lambda calculus, and their meaning calculated with an abstract mathematical machine. Compiler writers and designers of modern-day programming languages alike owe much to Landin's pioneering work.

Each year, a leading figure in computer science will pay tribute to Landin's contribution to computing through a public seminar. This year's seminar is entitled “Compiling Without Continuations” and will be given by Professor Simon Peyton Jones, FRS (Microsoft Research).

Agenda

  • 5.15pm - Coffee
  • 6.00pm - Welcome & Introduction
  • 6.05pm - Peter Landin Semantics Seminar - Compiling without Continuations
  • 7.20pm - Drinks reception

GHC compiles Haskell via Core, a tiny intermediate language based closely on the lambda calculus. Almost all GHC’s optimisations happen in Core, but until recently there was an important kind of optimisation that Core really did not handle well. In this talk Simon will show you what the problem was, and how Core’s new “join points” solve it simply and beautifully, by effectively allowing Core to express control flow as well as data flow; there are strong links to so-called “continuation passing style” (CPS) here.

Understanding join points can help you are a programmer too, because you can write code confident that it will optimise well. Simon will show you a rather compelling example this: “skip-less streams” now fuse well, for the first time, which allows us to drop the previous (ingenious but awkward) workarounds.

 

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