- Haskell-Cafe - Haskell.org

how to read CPU time vs wall time report from GHC?
by Wishnu Prasetya 14 Aug '11

14 Aug '11

Hi guys, I'm new in parallel programming with Haskell. I made a simple test program using that par combinator etc, and was a bit unhappy that it turns out to be slower than its sequential version. But firstly, I dont fully understand how to read the runtime report produced by GHC with -s option: SPARKS: 5 (5 converted, 0 pruned) INIT time 0.02s ( 0.01s elapsed) MUT time 3.46s ( 0.89s elapsed) GC time 5.49s ( 1.46s elapsed) EXIT time 0.00s ( 0.00s elapsed) Total time 8.97s ( 2.36s elapsed) As I understand it from the documentation, the left time-column is the CPU time, whereas the right one is elapses wall time. But how come that the wall time is less than the CPU time? Isn't wall time = user's perspective of time; so that is CPU time + IO + etc? Any help? --Wish.

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Evolving faster Haskell programs - where are the files?
by Robert Clausecker 14 Aug '11

14 Aug '11

I just read the enlightening article by Don Stewart[1], and wanted to test this method on one of my own programs, but it seems that there some of the attached files are missing, namely [2], [3] and [4]. Is there anybody who knows, where I can get those files? I don't really want to rewrite those file by hand. Yours, Robert Clausecker [1]: http://donsbot.wordpress.com/2009/03/09/evolving-faster-haskell-programs [2]: http://galois.com/~dons/acovea/gcc43_core2.acovea [3]: http://galois.com/~dons/acovea/ghc-basic.acovea [4]: http://galois.com/~dons/acovea/ghc-6_10.acovea

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Invitation to connect on LinkedIn
by Andrew Smith B.Sc(Hons),MBA 14 Aug '11

14 Aug '11

LinkedIn ------------ I'd like to add you to my professional network on LinkedIn. - Andrew Andrew Smith B.Sc(Hons),MBA Founder and CEO at VTRL - Value Technology Research Ltd Edinburgh, United Kingdom Confirm that you know Andrew Smith B.Sc(Hons),MBA https://www.linkedin.com/e/uc6lxc-grc8ge3y-3d/isd/3853824536/atjCCKYr/ -- (c) 2011, LinkedIn Corporation

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Re: [Haskell-cafe] Proposal #3339: Add (+>) as a synonym for mappend
by Brandon Allbery 14 Aug '11

14 Aug '11

On Sun, Aug 14, 2011 at 13:38, Yitzchak Gale <gale(a)sefer.org> wrote: > Brandon Allbery wrote: > > Umm, I think the semigroups package will break everything that creates > > Monoid instances anyway. > > It has never broken anything for me. What do you mean? > Anything useful has to be modified to depend on SemiGroup as well to get mconcat or its replacement; that's why you jumped the proposal to begin with.... As others have noted, this is a rather intrusive change to the Haskell ecosystem. *If* it has in fact been decided to go ahead with it, *then* this proposal should be merged with yours since the best time to do it is when mconcat is being relocated anyway. I don't think we've made it past the "if", especially given the comments so far. -- brandon s allbery allbery.b(a)gmail.com wandering unix systems administrator (available) (412) 475-9364 vm/sms

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Array and Ix for custom Graph ADT
by Mark Spezzano 14 Aug '11

14 Aug '11

Hi, I'm creating a Graph data structure, and I want to use the array list approach, implemented as an Array. I need my Nodes to be instances of Ix for this to work and my Node type is roughly as follows: data Node = MyNode Int [Int] Type1 Type2 (Type1 and Type2 are nullary algebraic datatypes--enumerations in other words) How can I "index" the Array with an instance of a Node. I think I need to make Node an instance of Ix somehow?? Is this a sensible approach? Sample code of the instance declaration for Ix would be helpful. Thanks Mark Spezzano

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Diffs for hackage
by Luite Stegeman 13 Aug '11

13 Aug '11

hi all, often when a new version of a package is available on hackage, I want to see what has changed since the previous release. Unfortunately many packages don't have a changelog or a public source code repository. That's why I have made a simple website with git repositories that contain all versions of all hackage packages: http://hdiff.luite.com/ The home page contains a bookmarklet that takes you directly from the index page of a package version (for example http://hackage.haskell.org/package/parsec-3.1.0 ) to the commit diff, showing the difference with the previous version ( http://hdiff.luite.com/cgit/parsec/commit?id=3.1.0 ) I hope some people will find this useful, luite

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Subtitles for "Programming in Haskell" videos
by José Romildo Malaquias 13 Aug '11

13 Aug '11

Hello. Are there subtitles (in English or Portuguese) for the video lectures[1] given by Erik Meijer using the book "Programming in Haskell", by Graham Hutton? [1] http://www.cs.nott.ac.uk/~gmh/book.html Romildo

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ML Workshop: register early by August 15
by Chung-chieh Shan 13 Aug '11

13 Aug '11

ACM SIGPLAN Workshop on ML Sunday, 18 September 2011, Tokyo, Japan (co-located with ICFP) http://conway.rutgers.edu/ml2011/ CALL FOR PARTICIPATION * Early Registration deadline is August 15! * The ML family of programming languages includes dialects known as Standard ML, Objective Caml, and F#. These languages have inspired a large amount of computer-science research, both practical and theoretical. This workshop aims to provide a forum for discussion and research on ML and related technology (higher-order, typed, or strict languages). The format of ML 2011 will continue the return in 2010 to a more informal model: a workshop with presentations selected from submitted abstracts. Presenters will be invited to submit working notes, source code, and extended papers for distribution to the attendees, but the workshop will not publish proceedings, so any contributions may be submitted for publication elsewhere. We hope that this format will encourage the presentation of exciting (if unpolished) research and deliver a lively workshop atmosphere. INVITED SPEAKERS Naoki Kobayashi (Tohoku University) Atsushi Ohori (Tohoku University) ACCEPTED TALKS Efficiently scrapping boilerplate code in OCaml Dmitri Boulytchev, Sergey Mechtaev Implementing implicit self-adjusting computation (short talk) Yan Chen, Joshua Dunfield, Matthew A. Hammer, Umut A. Acar Lightweight typed customizable unmarshaling Pascal Cuoq, Damien Doligez, Julien Signoles Adding GADTs to OCaml: the direct approach Jacques Garrigue, Jacques Le Normand A demo of Coco: a compiler of monadic coercions in ML (short talk) Nataliya Guts, Michael Hicks, Nikhil Swamy, Daan Leijen Verifying liveness properties of ML programs M. M. Lester, R. P. Neatherway, C.-H. L. Ong, S. J. Ramsay MixML remixed Andreas Rossberg, Derek Dreyer Report on OCaml type debugger Kanae Tsushima, Kenichi Asai Camomile: a Unicode library for OCaml (short talk) Yoriyuki Yamagata PROGRAM COMMITTEE Amal Ahmed (Indiana University) Andrew Tolmach (Portland State University) Anil Madhavapeddy (University of Cambridge) Chung-chieh Shan (chair) Joshua Dunfield (Max Planck Institute for Software Systems) Julia Lawall (University of Copenhagen) Keisuke Nakano (University of Electro-Communications) Martin Elsman (SimCorp) Walid Taha (Halmstad University) STEERING COMMITTEE Eijiro Sumii (chair) (Tohoku University) Andreas Rossberg (Google) Jacques Garrigue (Nagoya University) Matthew Fluet (Rochester Institute of Technology) Robert Harper (Carnegie Mellon University) Yaron Minsky (Jane Street)

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logic and types
by Patrick Browne 13 Aug '11

13 Aug '11

Hi, Below are some questions about the logical interpretation of types and type classes. Thanks, Pat module J where type Id = String type Position = Integer data Person = Person Id Position deriving Show -- Is this an axiom at type level? class Pos a where getPos :: a -> Position -- The :type command says -- forall a. (Pos a) => a -> Position -- How do I write this in logic? (e.g. implies, and, or, etc) -- What exactly is being asserted about the type variable and/or about the class? -- I am not sure of the respective roles of => and -> in a logical context -- Is the following a fact at type level, class level or both? instance Pos Person where getPos (Person i p) = p -- Is it the evaluation or the type checking that provides a proof of type correctness? -- getPos(Person "1" 2) This message has been scanned for content and viruses by the DIT Information Services E-Mail Scanning Service, and is believed to be clean. http://www.dit.ie

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Re: [Haskell-cafe] library on common sub-expression elimination?
by oleg＠okmij.org 13 Aug '11

13 Aug '11

I guess you mean the function that converts an abstract syntax tree to a directed acyclic graph (DAG). Just for completeness I should mention that if the object language has effects including non-termination, one has to be careful eliminating seemingly common expressions. For example, in \a i -> if i >= 0 then a ! i else if i > 0 then a ! i + a ! (i-1) else .... we see the expression (a ! i) repeated in both branches of the conditional. Eliminating the `duplicate' by pulling it out \a i -> let t = a ! i in if i >= 0 then t else if i > 0 then t + a ! (i-1) else .... would be wrong, wouldn't it? This issue has been extensively investigated in the Fortran compiler community; Elliott, Finne and de Moor's ``Compiling Embedded Languages'' (JFP 2003) talks about it at length. The standard technique to detect occurrences of common subexpressions is so-called hash-consing. There are (OCaml) libraries for it: author = {Jean-Christophe Filli{\^a}tre and Sylvain Conchon}, title = {Type-Safe Modular Hash-Consing}, pages = {12--19}, crossref = "ml2006", doi = "10.1145/1159876.1159880", The upcoming distilled tutorial at DSL 2011 http://dsl2011.bordeaux.inria.fr/index.php?option=com_content&view=article&… will present a Haskell library for hash-consing. The library can work with the standard Haskell Hash-tables or without them (using Data.Map, for example). The library does _not_ rely on Stable names and other internal GHC operations with unstable semantics. The library will find all common sub-expressions. Incidentally, despite the Lisp-sounding name, hash-consing was invented before Lisp. It was described, for the English audience, in the first volume of Comm. ACM, in 1958: @Article{ Ershov-hash-consing, author = {A. P. Ershov}, title = {On programming of arithmetic operations}, journal = "Communications of the {ACM}", year = 1958, volume = 1, number = 8, pages = {3--6}, doi ="10.1145/368892.368907", url = "http://portal.acm.org/citation.cfm?id=368907" } The translation is quite accurate, as far as I could see, but misses the flowcharts and the diagram of the original paper. This short paper fully describes what we now call hash tables, hash functions, useful properties of hash functions, and hash-consing. The article analyzes the time complexity of the algorithm. Since the algorithm has two exits, writing programs in the continuation-passing style must have been familiar back then. The library to be presented at DSL 2011 unwittingly follows Ershov's algorithm closely. The library is (hopefully) better described (see the preface to the English translation of Ershov's paper). Nowadays, starting a paper with the phrase ``All unexplained terms are those from [1]'' (where [1] is the single reference) would not be taken kindly by reviewers.

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