Changes between Version 16 and Version 17 of Status/May11
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 Apr 29, 2011 8:31:14 AM (6 years ago)
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Status/May11
v16 v17 1 2 1 '''WORK IN PROGRESS''' 3 2 … … 5 4 6 5 GHC is still busy as ever. The GHC 7.0 branch has come and gone, and now that the branch has been closed we have finally made the longplanned switch from darcs to git. Meanwhile, we are busily working towards the 7.2 branch, and hope to make the 7.2.1 release in June. Some of the forthcoming highlights are: 6 7 * In the autumn, Dimitrios and Simon PJ implemented a completely 8 new constraint solver for the type checker; we also complete an 9 epic JFP paper describing how it works [[http://research.microsoft.com/enus/um/people/simonpj/papers/constraints/ OutsideIn]]. The new 10 solver is far more tractable and maintainable than the old type 11 checker, and has fixed many outstanding problems. We are still 12 shaking out the last bugs, and we have some nifty ideas for improving 13 performance. Based on this new foundation, we are planning to 14 develop the type system further, notably by adding a richer kind 15 system along the lines of Conor !McBride's SHE system [[http://personal.cis.strath.ac.uk/~conor/pub/she/ SHE]]. 7 16 8 17 * GHC's intermediate language (which we call "Core") is a simple, … … 19 28 Core necessarily has to become a bit more complicated. For a few 20 29 years wa have been using an extension of System F, called System 21 FC, as described in our paper [ FC}. However, the way that System FC30 FC, as described in our paper [[http://research.microsoft.com/enus/um/people/simonpj/papers/extf/ FC]]. However, the way that System FC 22 31 was actually ''implemented'' in GHC's Core language was a bit unsatisfactory 23 32 so, with help from Brent Yorgey, Simon PJ is busy reengineering it. … … 26 35 squeezed into `Type`. Moreover, these coercion terms can get big, 27 36 so there's a new "coercion optimiser" to replace big coercions by 28 equivalent smaller ones. All this is described in our new paper [ NewFC].37 equivalent smaller ones. All this is described in our new paper [http://research.microsoft.com/enus/um/people/simonpj/papers/extf/ !NewFC]. 29 38 These changes will (finally) complete the typefamily story by 30 39 making socalled "equality superclasses" work for the first time. 31 40 32 * In the autumn, Dimitrios and Simon PJ implemented a completely 33 new constraint solver for the type checker; we also complete an 34 epic JFP paper describing how it works [OutsideIn]. The new 35 solver is far more tractable and maintainable than the old type 36 checker, and has fixed many outstanding problems. We are still 37 shaking out the last bugs, and we have some ideas for improving 38 performance. Based on this new foundation, we are planning to 39 develop the type system further, notably by adding a richer kind 40 system along the lines of Conor McBride's SHE system [SHE]. 41 * '''Pedro Magalhaes''' has nearly completed his implementation of the 42 '''derivable type classes''' mechanism described in his 2010 43 Haskell Symposium paper [[http://www.dreixel.net/research/pdf/gdmh_nocolor.pdf Derivable]]. It will be in GHC 7.2. 41 44 42 * Pedro Magalhaes has nearly completed his implementation of the 43 '''derivable type classes''' mechanism described in his 2010 44 Haskell Symposium paper [Derivable]. It will be in GHC 7.2. 45 46 * Edward Yang has done a lot of work on the longpromised new 45 * '''Edward Yang''' has done a lot of work on the longpromised new 47 46 codegeneration path. Hoopl is now fully part of GHC, and 48 47 the new path uses it extensively. We are now working on making 49 48 the new pipeline generate better code than the old one. Stay 50 tuned. * '''Simon PJ: New coercions''' 51 52 53 54 * '''Simon PJ: Any update? Any regressions remaining?''' Previous entry: ''As long promised, Simon PJ and Dimitrios have spent a good chunk of the summer doing a '''complete rewrite of the constraint solver in the type inference engine'''. Because of GHC's myriad typesystem extensions, especially GADTs and type families, the old engine had begun to resemble the final stages of a game of Jenga. It was a delicatelybalanced pile of blocks that lived in constant danger of complete collapse, and had become extremely different to modify (or even to understand). The new inference engine is much more modular and robust; it is described in detail in our paper [[http://haskell.org/haskellwiki/Simonpj/Talk:OutsideIn OutsideIn]]. A blog post describes some consequential changes to let generalisation [[http://hackage.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7 LetGen]].'' 55 49 tuned. 56 50 57 51 * '''Simon Marlow: Any update?''' Previous entry: ''In joint work with Phil Trinder and his colleagues at Herriot Watt, Simon M designed implemented a new '''parallel strategies library''', described in their 2010 Haskell Symposium paper [[http://www.haskell.org/~simonmar/papers/strategies.pdf Seq]].'' … … 84 78 Here's a selection that we know about. 85 79 86 * ''Pedro Magalhaes is implementing the '''derivable type classes''' mechanism described in his 2010 Haskell Symposium paper [[http://www.dreixel.net/research/pdf/gdmh_nocolor.pdf Derivable]]. I plan for this to replace GHC's current derivabletypeclass mechanism, which has a poor powertoweight ratio and is little used.'' 87 88 * ''Stephanie Weirich and Steve Zdancewic had a great sabbatical year at Cambridge. One of the things we worked on, with Brent Yorgey who came as an intern, was to close the embarrassing hole in the type system concerning '''newtype deriving''' (see Trac bug #1496). I have delayed fixing until I could figure out a Decent Solution, but now we know; see our 2011 POPL paper [[http://www.cis.upenn.edu/~sweirich/newtypes.pdf Newtype]]. Brent is working on some infrastructal changes to GHC's Core language, and then we'll be ready to tackle the main issue.'' 89 90 * ''Next after that is a mechanism for '''promoting types to become kinds''', and data constructors to become types, so that you can do ''typed'' functional programming at the type level. Conor !McBride's SHE prototype is the inspiration here [[http://personal.cis.strath.ac.uk/~conor/pub/she/ SHE]]. Currently it is, embarrassingly, essentially untyped.'' 91 92 * '' '''Template Haskell''' seems to be increasingly widely used. Simon PJ has written a proposal for a raft of improvements, which we plan to implement in the new year [[http://hackage.haskell.org/trac/ghc/blog/Template%20Haskell%20Proposal TemplateHaskell]].'' 93 94 * ''Iavor Diatchki plans to add '''numeric types''', so that you can have a type like `Bus 8`, and do simple arithmetic at the type level. You can encode this stuff, but it's easier to use and more powerful to do it directly.'' 80 * '''Jeff Epstein''' has implemented a library that brings Erlang's programming model to Haskell programmers. In particular, you can write a Haskell program that runs on a cluster of machines that do not share memory. It is all based on a modest but powerful language extension that makes it possible for a programmer to work with "static" functions; that is, ones consisting of pure code with no free variables. The paper that describes all this is called "Haskell for the cloud" [[http://research.microsoft.com/enus/um/people/simonpj/papers/parallel/ Cloud]]. 95 81 96 82 * ''David Mazieres at Stanford wants to implement '''Safe Haskell''', a flag for GHC that will guarantee that your program does not use `unsafePerformIO`, foreign calls, RULES, and other stuff stuff.'' … … 111 97 with consulting and engineering support from WellTyped. Each organisation is working on its own particular project making use of parallel Haskell. The overall goal is to demonstrate successful serious use of parallel Haskell, and along the way to apply engineering effort to any problems with the tools that the organisations might run into. 112 98 113 For more details, see the '''link:'''parallel GHC project entry .99 For more details, see the '''link:'''parallel GHC project entry, and the project home page [[http://www.haskell.org/haskellwiki/Parallel_GHC_Project !ParallelGHCProject]] 114 100 115 101 == Data Parallel Haskell == … … 124 110 '''TODO: Remove redundant entries''' 125 111 126 * [Bryan] "A brief tale of faster equality", Bryan O'Sullivan blog post, Oct 2010, http://www.serpentine.com/blog/2010/10/19/abrieftaleoffasterequality/. 127 128 * [Containers] "The performance of the Haskell containers package", Straka, Haskell Symposium 2010, http://research.microsoft.com/~simonpj/papers/containers/containers.pdf 112 * [Cloud] "Haskell for the cloud", Epstein, Black, Peyton Jones, submitted to ICFP 2011, http://research.microsoft.com/enus/um/people/simonpj/papers/parallel/ 129 113 130 114 * [Derivable] "A generic deriving mechanism for Haskell", Magalhães, Dijkstra, Jeuring and Löh, Haskell Symposium 2010, http://www.dreixel.net/research/pdf/gdmh_nocolor.pdf. 131 115 132 * [ !LetGen] "Let generalisation in GHC 7.0", Peyton Jones, blog post Sept 2010, http://hackage.haskell.org/trac/ghc/blog/LetGeneralisationInGhc7116 * [FC] "System F with type equality coercions", Sulzmann, Chakravarty, Peyton Jones, TLDI 2007, http://research.microsoft.com/enus/um/people/simonpj/papers/extf/ 133 117 134 * [ Newtype] "Generative Type Abstraction and Typelevel Computation", Weirich, Zdancewic, Vytiniotis, and Peyton Jones, POPL 2010, http://www.cis.upenn.edu/~sweirich/newtypes.pdf118 * [!NewFC] "Practical aspects of evidencebased compilation in System FC", Vytiniotis and Peyton Jones, submitted to ICFP 2011, http://research.microsoft.com/enus/um/people/simonpj/papers/extf/ 135 119 136 * [Llvm] "An LLVM Backend for GHC", Terei and Chakravarty, Haskell Symposium 2010, http://www.cse.unsw.edu.au/~davidt/downloads/ghcllvmhs10.pdf 120 * [!OutsideIn] "Modular type inference iwth local assumptions", Vytiniotis, Peyton Jones, Schrijvers, and Sulzmann, Journal of Functional Programming (to appear), http://research.microsoft.com/enus/um/people/simonpj/papers/constraints/ 121 122 * [!ParallelGhcProject] "The Parallel GHC Project home page", http://www.haskell.org/haskellwiki/Parallel_GHC_Project 137 123 138 124 * [Seq] "Seq no more", Marlow, Maier, Trinder, Loidl, and Aswad, Haskell Symposium 2010, http://www.haskell.org/~simonmar/papers/strategies.pdf