A Quick Look at Impredicativity (Simon Peyton Jones)

Simon Peyton Jones presents Quick Look, a practical and deployable design for impredicative type inference in GHC.

Type inference for parametric polymorphism is wildly successful, but has always suffered from an embarrassing flaw: polymorphic types are themselves not first class. I’ve been trying to fix this flaw for over 15 years , but every time I ended up with a system that was unusably complicated. But now I think we have it! Quick Look is a practical, implemented, and deployable design for impredicative type inference. It is simple to explain (although you can be the judge of that), and crucially it can be implemented with modest, localised changes that are fully compatible with GHC’s myriad other type system extensions. Bio: Simon Peyton Jones, FRS, graduated from Trinity College Cambridge in 1980. 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. 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. audience: Anyone interested in statically-typed functional programming. Link: microsoft.com/en-us/research/publication/a-quick-look-at-imp…