October 2014 - Haskell-Cafe

ANN: Haskell plugin for IntelliJ
by Rik van der Kleij 20 Oct '14

20 Oct '14

Hi everyone, I'm glad to announce initial version of Haskell plugin for IntelliJ. It's available in the plugin repository. This plugin is written mainly in Scala and is not mentioned to support GHC/Cabal directly. This plugin support sandbox projects and expects that the Cabal init/install/build is done on command-line. Features - Syntax highlighting (which can be customised); - Error/warning highlighting; - Find Usages of identifiers; - Resolving references of identifiers (also to library code if library source code is added to project and resolves inside import declaration); - Code completion by resolving references; - Renaming variables (which first shows preview so refactoring scope can be adjusted); - View type info from (selected) expression; - View expression info; - View quick documentation; - View quick definition; - Structure view; - Navigate to declaration (called `Class` in IntelliJ menu); - Navigate to identifier (called `Symbol` in IntelliJ menu); - Code completion by looking to import declarations; - Simple form of code formatting; A lot of features are with the help of ghc-mod and ghc-modi. Documentation is provided by haskell-docs. See for more information and getting started: https://github.com/rikvdkleij/intellij-haskell Any feedback is welcome! Regards, Rik

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Eval forgotten unless type specified?
by Jeffrey Brown 19 Oct '14

19 Oct '14

In this passage, after the seq call, :sprint reveals x and y to be evaluated: let x = 1 + 2 :: Int let y = x + 1 :sprint x :sprint y seq y () :sprint x :sprint y The above is a verbatim quote of Marlow's Concurrency book, chapter 2. In the below, however, :sprint shows them unevaluated both before and after the seq call. let x = 1 + 2 let y = x + 1 :sprint x :sprint y seq y () :sprint x :sprint y Why?

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Profiling with an interpreter
by Corentin Dupont 18 Oct '14

18 Oct '14

Hi, I'm trying to profile my game (Nomyx) but I get: "You can't call hscCompileCoreExpr in a profiled compiler". I figured out it's because I'm embbeding an intrepreter. Is there a way to avoid that and profile anyway? Maybe ignoring the calls to the interpreter or something... Cheers Corentin

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What happened to hugs?
by Thorsten Rangwich 18 Oct '14

18 Oct '14

Hi, I suppose this question is not new, but neither google nor a manual search file be file through the archives brought enlightement. www.haskell.org/hugs still exists, but none of the links there does work. Documentation and source point to cvs.haskell.org ("server does not exist") and development points to http://hackage.haskell.org/trac/hugs ("page does not exist"). Was it migrated to somewhere else or is it dead - in latter case the page would not make sense any more. "Raskell" (iPad app) provided a development environment usinh hugs, so I would at least like to install hugs on my Mac as well... Thank you very much in advance. Thorsten. Sent from my mobile phone

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Best way to Introduce FP into a dev team with many C, C++ and Java developers?
by Birmjin In 18 Oct '14

18 Oct '14

Hi, Recently our development team had decided to attempt using Haskell or Scala as one of our programming language. (We had hoped some of our problem will be addressed through taking advantage of some element of FP, like immutability and Rx) Most of our team members have fairly good knowledge of C, C++ and Java. And few of them, including myself, have been self-studying a FP language like Haskell and Scala since last year. Besides some early starters, functional programming is quite new to us. When we held a lecture on FP, we found many of our developers were struggling in grasping some idea of FP. They fumbled with writing functional programming style code. We kept on lecturing several times, but still not quite successful. It seems more difficult than it looks - thinking in functional programming way for the long time C, C++ and Java developers. Does anyone had an experience with initiating FP adoption into a large dev team without pain? Our development team has around 300+ people. Thanks.

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beginnners book
by Roelof Wobben 17 Oct '14

17 Oct '14

Hello, What is a good book to learn Haskell with a lot of exercises so I can check if I understand everything right ? Roelof

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2^770000 triggers Bus Error?
by Erik Rantapaa 17 Oct '14

17 Oct '14

Running ghci under OSX I am seeing the following behavior: Prelude> 2^750000 {... lots of digits...} Prelude> 2^760000 Segmentation Fault: 11 Prelude> 2^770000 Bus Error: 10 and I'm curious why this happens. More details: $ ghci --version The Glorious Glasgow Haskell Compilation System, version 7.8.3 I'm using the 64-bit version of the Haskell Platform (x86_64-darwin-7.8.3).

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Haskell software engineering master thesis
by Jon Kristensen 17 Oct '14

17 Oct '14

Hi, everyone! I'm about to write a software engineering/management master thesis at the IT University of Gothenburg, and I'm considering to do research into the Haskell world. It should probably be in one of the following five fields: empirical software engineering, requirements engineering, software architecture, model-driven engineering or quality management. The focus should probably be more towards an empirical study, rather than something more computer science-related. It should also add to general body of knowledge, and not be too tied to, for example, a specific implementation. Does anyone have any suggestions of relevant topics that I could write about, or perhaps some related papers that I could read? Thanks! Warm regards, Jon Kristensen

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Splicing type signature in TH
by Hugo Pacheco 16 Oct '14

16 Oct '14

Hi list, I am 99.9% sure that this is currently not possible, but I might as well ask: - Is there a way to lift type variables into Template Haskell type splices? What I had in mind would be something like this (erroneous) code: liftT :: a -> Q Type liftT (_::a) = [t| $a |] I have no idea how hard it would be to implement such a feature, or if it is remotely doable. Naively, it seems to me that TH would have to delay evaluating the splice until the type variable is fully expanded, but all the necessary information would still be available at some point during compilation. Cheers, hugo -- www.cs.cornell.edu/~hpacheco

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Converting a Constraint to Bool
by Ivan Lazar Miljenovic 16 Oct '14

16 Oct '14

Using the Constraint type and the ConstraintKinds extension, is there any way we can determine if a Constraint is satisfied (i.e. a type-level function of type Constraint -> Bool using DataKinds)? -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com http://IvanMiljenovic.wordpress.com

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