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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, you will learn 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. On the way, you will explore how GHC’s Mighty Simplifier, which is responsible for many optimisations, works.
Understanding join points can help you are a programmer too, because you can write code confident that it will optimise well. You will discover 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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Senior Principal Researcher
Microsoft Research, Cambridge
Simon Peyton Jones, MA, MBCS, CEng, graduated from Trinity College Cambridge in 1980. Simon 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.
After two years in industry, he spent seven years as a lecturer at University College London, and nine years as a professor at Glasgow University before moving to Microsoft Research (Cambridge) in 1998.
His main research interest is in functional programming languages, their implementation, and their application. He has led a succession of research projects focused around the design and implementation of production-quality functional-language systems for both uniprocessors and parallel machines.
More generally, he is interested in language design, rich type systems, software component architectures, compiler technology, code generation, runtime systems, virtual machines, and garbage collection. He is particularly motivated by direct use of principled theory to practical language design and implementation -- that's one reason he loves functional programming so much.