- Haskell-Cafe - Haskell.org

CTO Opportunity
by Charles Weitzer 03 Feb '14

03 Feb '14

My name is Charles Weitzer. I do recruiting for major quantitative hedge funds worldwide. I have a client, a startup quantitative hedge fund located in Northern California, that would like to hire a Chief Technology Officer as soon as possible. Their job description can be found below. * Chief Technology Officer Fast-growing science and technology driven company seeks a Chief Technology Officer. We apply statistical machine learning to develop automated trading systems. We are a growing group of exceptional software and infrastructure professionals and seek an experienced candidate to lead and grow the team. The CTO will manage the implementation of our next generation infrastructure, including production trading systems, software infrastructure for our research department, and our compute and storage hardware systems. The CTO will work directly with the Head of Research and the CEO to set the technical direction of the company. A strong candidate will be well-versed in state-of-the-art technology (particularly distributed systems and cluster computing), and will have a track record of building and leading elite technical teams and successfully delivering complex projects (especially in a startup environment). A background in finance is not required. We are a science-driven systematic trading firm, built on the principle that statistical machine learning provides the best solutions to the scientific problems we must solve. Our CEO is a CS PhD and founded a successful Internet startup, and our Head of Research/Chief Investment Officer is a Berkeley statistics professor; both have a background in finance. Our trading is entirely automated and based on cutting-edge machine learning techniques. We have a collegial, academic working environment, rely on open source software, and have built our own software stack. We have a track record of strong performance and have been raising money and growing fast. Willingness to take initiative, and a gritty determination to productize, are essential. Benefits and compensation are highly competitive. I look forward to speaking with you and anyone you might highly recommend about this opportunity. Thank you, Charles Weitzer CEO/Senior Recruiter Charles Weitzer and Associates, Inc. Global Financial Recruiting Services Charles(a)CharlesWeitzer.com Voice: USA (510) 558-9182

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Dispatch a type-function on the existence (or not) of instances?
by Hans Höglund 03 Feb '14

03 Feb '14

Dear all, I have been curious about the ability to detect the presence of a certain instance (ClassFoo TypeBar) in the type system. Specifically, is it possible to "dispatch" a type on the existence (or not) of such an instance. For example given two functions: withInstance :: (ClassFoo TypeBar) => TypeIfInstanceExists withoutInstance :: TypeIfInstanceDoesNotExists I would be able to consolidate them into something like this: withOrWithoutInstance :: (r ~ InstanceExists ClassFoo TypeBar, a ~ If r TypeIfInstanceExists TypeIfInstanceDoesNotExists) => a I guess what I need is: 1) A type-level "if". 2) The possibility of "converting" a constraint into a type-level bool. I am sure (1) is possible but have no idea about (2). Anyone? Best regards, Hans

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What game libraries should I use?
by Alexander Berntsen 03 Feb '14

03 Feb '14

-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA256 I need: - -2D graphics (preferably with simple shapes available) - -menus (I can make menus myself with shapes though) - -simple audio - -fonts (better than Gloss at least) - -keyboard input - -networking (simple direct connections between two computers) I need to be able to express my game system as declaratively as possible[0]. If the library is based on SDL/OpenGL, that would be nice[1]. This is, however, not necessary. What game libraries are the most mature and adequate for this? The only library I have used previously with Haskell is Gloss. I am not experienced in FRP, though I have read about and somewhat groked the point. I am willing to learn an FRP library. [0] I am writing it as part of a thesis in which I will look at the modularity and expressiveness of purely functional programming compared to object-oriented programming. Writing code that is technically purely functional, but in practice looks like imperative code, is sub-optimal. [1] For the thesis I am writing, I am implementing a C++ version of the same game. This will probably use SDL 2.0 and OpenGL bindings. If the Haskell version could use libraries based on that, this would make it easier for me to write my thesis. I.e., I would not have to spend time justifying that the modularity and expressiveness I am investigating is due to the chosen languages and programming paradigms, and not the libraries I use. - -- Alexander alexander(a)plaimi.net http://plaimi.net/~alexander -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) Comment: Using GnuPG with Thunderbird - http://www.enigmail.net/ iF4EAREIAAYFAlLrlMoACgkQRtClrXBQc7VkiAEAnEbfjiSLovcXttmjpdD5OSFI uEMBVBJdWonY9ZMPIc8BAIAQn+YMRvGILgb8WmuB9oTWJDVZfqDMyB47qzjyfimO =YGLW -----END PGP SIGNATURE-----

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ANNOUNCE: fpnla - A library for NLA operations
by Mauro Blanco 02 Feb '14

02 Feb '14

Hi. Today we are releasing fpnla <http://hackage.haskell.org/package/fpnla>, which defines a framework for linear algebra operations of BLAS and LAPACK. As its main features it allows: - Definition of multiple representations of vectors and matrices. - Arbitrary combination of strategies and structure representations. - Type-safe manipulation of context information associated to each strategy. - Definition of specialized strategies for a given representation. And also fpnla-examples <http://hackage.haskell.org/package/fpnla-examples>, which contains many example implementations of the operations defined in fpnla using various data structures and algorithms. Regards. -- Mauro Blanco

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New book: "Beginning Haskell"
by Alejandro Serrano Mena 02 Feb '14

02 Feb '14

[Disclaimer: I'm the author of the book] Dear Haskell-cafe, I would like to introduce a new book discussing our favourite language from beginner into upper intermediate level: "Beginning Haskell". The book starts assuming zero knowledge about functional programming and builds step by step to get into the realm of web applications, type-level programming, domain specific languages, distributed computing, unit testing and much more! You can look at the Table of Contents in Amazon [ http://www.amazon.com/Beginning-Haskell-A-Project-Based-Approach/dp/1430262… ]. The book revolves around the idea of a Time Machine Store: in each part some functionality is developed. The first part serves as an introduction and how to model the data with Haskell data types and functions; part 2 discusses many concepts around monads while developing two data-mining algorithms; in the third part storing and interfacing with clients serves as an excuse to introduce input/output, database access and web applications; part 4 is devoted to discussing domain specific libraries for describing offers; and the last part discusses testing and other engineering issues. All the "classical" topics in Haskell are discussed: higher-order functions, type classes -- functors, applicatives, monads --, laziness. The focus also lies on libraries use in modern Haskell daily programming, such as lenses, streaming data libraries, functional dependencies and type families, Software Transactional Memory and Cloud Haskell. One topic that is cross-cutting through the book is how to manage projects with Cabal or EclipseFP: initializing a new package, declaring dependencies, building and integrating tests. The book tries thus to offer a comprehensive view of the Haskell ecosystem, not only of the Haskell programming language. The book is published by Apress [http://www.apress.com/9781430262503] and available as paperback and electronic format. If somebody would like to make a review for some FP or programming-related magazine (such as The Monad Reader) or assess its possibilities for use in classroom, please drop me a line. Hope you like it! :)

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Castle: Permission denied
by Henk-Jan van Tuyl 02 Feb '14

02 Feb '14

L.S., I am trying to install castle, but I get the following messages: Downloading castle-0.1.0.0... Configuring castle-0.1.0.0... realgcc.exe: ./specs: Permission denied What can I do about this? I am running Windows XP, Haskell Platform 2013.2.0.0 Regards, Henk-Jan van Tuyl -- Folding@home What if you could share your unused computer power to help find a cure? In just 5 minutes you can join the world's biggest networked computer and get us closer sooner. Watch the video. http://folding.stanford.edu/ http://Van.Tuyl.eu/ http://members.chello.nl/hjgtuyl/tourdemonad.html Haskell programming --

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DSLs and heterogeous lists
by Corentin Dupont 01 Feb '14

01 Feb '14

Hi again, I have a game in which the user can create/write/read variables, using a small DSL. The type of the variable created can be whatever chooses the user, so I'm using existential types to store those variables in a heterogeneous list. This works fine, but the problem is that the "Typeable" class tag leaks into the DSL... The question is, how to get rid of it? > This is literate Haskell > {-# LANGUAGE GADTs, ScopedTypeVariables #-} > module DSLClass where > import Control.Monad > import Control.Monad.State > import Data.Typeable > This is the (simplified) DSL. With it you can read a variable stored in the game state (creation/writing is not shown). How can we get rid of the "Typeable a" in the ReadFirstVar constructor? > -- first type parameter is used to track effects > data Exp a where > ReadFirstVar :: (Typeable a) => Exp a <----- Ugly > Return :: a -> Exp a > Bind :: Exp a -> (a -> Exp b) -> Exp b This is the definition of a variable. The type is unknow, so I use existantial types. > data Var = forall a . (Typeable a) => Var { v :: a} This game state. It holds the heterogenous list. > data Game = Game { variables :: [Var]} The evaluation of "Exp" can be: > eval :: Exp a -> State Game a > eval ReadFirstVar = do > (Game ((Var v):vs)) <- get > case cast v of > Just val -> return val > Nothing -> error "no cast" > eval (Bind exp f) = do > a <- eval exp > eval (f a) As you can see, I'm obliged to cast the variable type to match it with the expression's type. Is that the right place to do it? Thanks!! Corentin

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Cabal version constraint seems to be ignored.
by Carlo Hamalainen 31 Jan '14

31 Jan '14

Hi, I have two versions of Cabal, both are visible: $ ghc-pkg expose Cabal-1.16.0 $ ghc-pkg expose Cabal-1.18.1.2 I clone and build my package. Since I have GHC 7.6.3 it uses Cabal-1.16.0 (as specified in ghc-imported-from.cabal): $ git clone https://github.com/carlohamalainen/ghc-imported-from $ cd ghc-imported-from $ cabal install It looks like Cabal-1.16.0 was chosen, as expected: $ grep Cabal dist/build/autogen/cabal_macros.h /* DO NOT EDIT: This file is automatically generated by Cabal */ /* package Cabal-1.16.0 */ #define VERSION_Cabal "1.16.0" #define MIN_VERSION_Cabal(major1,major2,minor) (\ But my program doesn't run: $ ghc-imported-from src/Main.hs Main getArgs 11 11 --ghc-options --ghc-pkg-options GhcOptions [] GhcPkgOptions [] Language/Haskell/GhcImportedFrom.hs:132:54: Couldn't match expected type `Distribution.PackageDescription.BuildInfo' with actual type `Cabal-1.16.0:Distribution.PackageDescription.BuildInfo' In the fourth argument of `getGHCOptions', namely `binfo' In a stmt of a 'do' block: getGHCOptions [] c (fromJust $ cradleCabalDir c) binfo In the expression: do { c <- findCradle; pkgDesc <- GhcMonad.liftIO $ parseCabalFile $ fromJust $ cradleCabalFile c; let binfo = head $ cabalAllBuildInfo pkgDesc; getGHCOptions [] c (fromJust $ cradleCabalDir c) binfo } I'm surprised that the error didn't appear at compile time. I guess the first reference to Distribution.PackageDescription.BuildInfo is from Cabal-1.18.1.2? If I hide Cabal-1.18.1.2 then things work ok: $ ghc-pkg hide Cabal-1.18.1.2 $ cabal install $ ghc-imported-from .... (runs as expected) But I can't expect a user to know that they have to hide Cabal-1.18.1.2. Is this actually a GHC bug or have I stuffed up my ghc-imported-from.cabal file? Thanks, -- Carlo Hamalainen http://carlo-hamalainen.net

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TFP 2014 - 2nd call for papers
by Peter Achten 31 Jan '14

31 Jan '14

--------------------------------- 2ND C A L L F O R P A P E R S --------------------------------- ======== TFP 2014 =========== 15th Symposium on Trends in Functional Programming May 26-28, 2014 Utrecht University Soesterberg, The Netherlands http://www.cs.uu.nl/wiki/TFP2014/WebHome *** Submission for TFP 2014 is now open: please direct your browser to *** http://www.cs.uu.nl/wiki/TFP2014/PaperSubmission The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below), described in draft papers submitted prior to the symposium. A formal post-symposium refereeing process then selects a subset of the articles presented at the symposium and submitted for formal publication. Selected revised papers will be published as a Springer Lecture Notes in Computer Science (LNCS) volume. TFP 2014 will be the main event of a pair of functional programming events. The other is the International Workshop on Trends in Functional Programming in Education (TFPIE). TFPIE will take place on May 25th. Its website is located at http://www.cs.uwyo.edu/~jlc/tfpie14/ The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in Edinburgh (Scotland) in 2003, in Munich (Germany) in 2004, in Tallinn (Estonia) in 2005, in Nottingham (UK) in 2006, in New York (USA) in 2007, in Nijmegen (The Netherlands) in 2008, in Komarno (Slovakia) in 2009, in Oklahoma (USA) in 2010, in Madrid (Spain) in 2011, St. Andrews (UK) in 2012 and Provo (Utah, USA) in 2013. For further general information about TFP please see the TFP homepage. INVITED SPEAKERS TFP is pleased to announce talks by the following two invited speakers: John Hughes of Chalmers, Goteborg, Sweden, is well-known as author of Why Functional Programming Matters, and as one of the designers of QuickCheck (together with Koen Claessen); the paper on QuickCheck won the ICFP Most Influential Paper Award in 2010. Currently he divides his time between his professorship and Quviq, a company that performs property-based testing of software with a tool implemented in Erlang. Dr. Geoffrey Mainland received his PhD from Harvard University where he was advised by Greg Morrisett and Matt Welsh. After a two year postdoc with the Programming Principles and Tools group at Microsoft Research Cambridge, he is now an assistant professor at Drexel University. His research focuses on high-level programming language and runtime support for non-general purpose computation. SCOPE The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not submitted for simultaneous publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or more experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Using functional techniques to reason about imperative/object-oriented programs Debugging for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2014 program chair, Jurriaan Hage at J.Hage(a)uu.nl. BEST PAPER AWARDS To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. SPONSORS TFP is financially supported by NWO (Netherlands Organisation for Scientific Research), Well-Typed and Erlang Solutions. PAPER SUBMISSIONS Acceptance of articles for presentation at the symposium is based on a lightweight peer review process of extended abstracts (4 to 10 pages in length) or full papers (16 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate whether the main author or authors are research students. In the case of a FULL STUDENT paper, the draft paper will receive additional feedback by one of the PC members shortly after the symposium has taken place. We use EasyChair for the refereeing process. IMPORTANT DATES Submission of draft papers: March 17, 2014 Notification: March 24, 2014 Registration: April 7, 2014 TFP Symposium: May 26-28, 2014 Student papers feedback: June 9th, 2014 Submission for formal review: July 1st, 2014 Notification of acceptance: September 8th, 2014 Camera ready paper: October 8th, 2014 PROGRAM COMMITTEE Peter Achten Radboud University Nijmegen Emil Axelsson Chalmers Lucilia Camarao de Figueiredo Universidade Federal de Ouro Preto Laura Castro University of A Coruna Frank Huch Christian-Albrechts-University of Kiel Matthew Fluet Rochester Institute of Technology Jurriaan Hage (chair) University of Utrecht Yukiyoshi Kameyama University of Tsukuba Andrew Kennedy Microsoft Research Tamas Kozsik Eotvos Lorand University Ben Lippmeier University of New South Wales Luc Maranget INRIA Jay McCarthy (co-chair) Brigham Young University Marco T. Morazan Seton Hall University Ricardo Pena Universidad Complutense de Madrid Alexey Rodriguez LiquidM Sven-Bodo Scholz Heriot-Watt University Manuel Serrano INRIA Sophia Antipolis Simon Thompson University of Kent Tarmo Uustalu Inst of Cybernetics David Van Horn University of Maryland Janis Voigtlaender University of Bonn

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Re: [Haskell-cafe] manage effects in a DSL
by oleg＠okmij.org 31 Jan '14

31 Jan '14

> - What do you mean by "The type Cont Int a describes an impure computation, > which may abort with an Int value, for example". > Aborting with an Int value is akin to exceptions? I see that using Cont monad wasn't a good idea. The point can be made simply, with an Error monad or applicative. Here is a simple function to multiply a list of integers: > muls :: [Integer] -> Either e Integer > muls [] = pure 1 > muls (h:t) = (h*) <$> muls t We give the signature (which the compiler accepts) with the polymorphic return type Either e Integer, fully polymorphic over e. Therefore, muls throws no exceptions. Here is a bit more optimized function, which stops all multiplications once zero is encountered. > mulse :: [Integer] -> Either Integer Integer > mulse [] = pure 1 > mulse (0:t) = Left 0 > mulse (h:t) = (h*) <$> mulse t We cannot make the return type (Either e Integer), it must be (Either Integer Integer). The function can indeed throw an exception. If we handle the exception > muls' :: [Integer] -> Either e Integer > muls' l = either pure pure $ mulse l the effect is encapsulated and the type is polymorphic again. > - for me it's not clear when to choose an "applicative" or a "monadic" DSL? > Betsides, what's the rational behind the name "let_" (never seen it before)? The first rule of thumb is to use the simplest structure that does the job. Another good rule is to distinguish the DSL from its implementation. For example, the DSL below http://okmij.org/ftp/tagless-final/index.html#call-by-any has no monads. It is a simple lambda-calculus with constants. Its implementation in Haskell, the embedding, does use monads, sometimes quite specific monads (e.g., IO, to print the trace of evaluation). But these monads are not exposed to the DSL programmer. That article also shows off let_. > data Eff = Effect | NoEffect > -- first type parameter is used to track effects > data Exp :: Eff -> * -> * where > ReadAccount :: Exp r Int --ReadAccount can be used in whatever > monad (with or without effect) > WriteAccount :: Exp NoEffect Int -> Exp Effect () --WriteAccount > takes an effect-less expression, and returns an effectfull expression This is exactly what I had in mind (and probably Jacques as well). > Other pointers where this idiom is realised?? Lots of places; ST monad comes to mind, and the Region monad. This trick is often used to track, for example, information flow security (the label then reflects the sensitivity level of data processed by the computation, Low or High). See, for example, http://www.cse.chalmers.se/~russo/seclib.htm http://www.scs.stanford.edu/~deian/pubs/stefan:2011:flexible-slides.pdf or just search for information flow control or information flow security in Haskell. Edward Yang has a lot to say on this topic.

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