- Haskell-Cafe - Haskell.org

uninstalling ghc-8.0.1-x86_64 installed through "install-haskell-platform.sh"
by Patrice 07 Jun '16

07 Jun '16

Hi all, How can I uninstall cleanly ghc-8.0.1-x86_64 that I installed using the script install-haskell-platform.sh (found on haskell.org website under Generic Linux). I'm on ubuntu Trusty. Thanks, Pat

2 2

Having issue in running Haskell code in Atom
by Balraj Singh 06 Jun '16

06 Jun '16

Hello All, I have started learning Haskell couple of days ago. I was looking for an IDE and found Atom as one of them. When I started using it I installed multiple packages and tried running creating Haskell files and saving it. This IDE always gives me following error. Please help to debug this: [Enter steps to reproduce below:] 1. ... 2. ... **Atom Version**: 1.7.4 **System**: Microsoft Windows 10 Pro **Thrown From**: [haskell-ghc-mod]( https://github.com/atom-haskell/haskell-ghc-mod) package, v1.14.5 ### Stack Trace Haskell-ghc-mod: ghc-mod failed to launch. It is probably missing or misconfigured. ENOENT ``` At Error: spawn ghc-mod ENOENT PATH: undefined path: undefined Path: C:\Program Files (x86)\Intel\iCLS Client\;C:\Program Files\Intel\iCLS Client\;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\DAL;C:\Program Files\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files (x86)\Intel\Intel(R) Management Engine Components\IPT;C:\Program Files (x86)\ATI Technologies\ATI.ACE\Core-Static;C:\Users\Balraj Singh\.dnx\bin;C:\Program Files\Microsoft DNX\Dnvm\;C:\Program Files\Microsoft SQL Server\120\Tools\Binn\;C:\Program Files (x86)\Windows Kits\10\Windows Performance Toolkit\;C:\Program Files\Microsoft SQL Server\130\Tools\Binn\;C:\Program Files (x86)\Java\jdk1.7.0_71\lib;C:\Program Files (x86)\Java\jre7\lib;C:\Program Files (x86)\Java\jdk1.7.0_71\bin;C:\Program Files (x86)\Java\jre7\bin;C:\Program Files\Git\cmd;C:\Program Files (x86)\WinMerge;C:\ghc-8.0.1\bin;C:\Users\Balraj Singh\AppData\Local\atom\bin Error at file:///C:/Users/Balraj Singh/.atom/packages/haskell-ghc-mod/lib/util.coffee:60:26 at exithandler (child_process.js:232:5) at ChildProcess.errorhandler (child_process.js:244:5) at emitOne (events.js:77:13) at ChildProcess.emit (events.js:169:7) at Process.ChildProcess._handle.onexit (internal/child_process.js:198:12) at onErrorNT (internal/child_process.js:344:16) at doNTCallback2 (node.js:465:9) at process._tickCallback (node.js:379:17) ``` ### Commands ``` -8:25.4.0 core:backspace (atom-text-editor.editor.is-focused) 3x -8:22 core:save (atom-text-editor.editor.is-focused) -8:00.7.0 tabs:open-in-new-window (li.texteditor.tab.sortable.active.right-clicked) -7:50.5.0 tree-view:show-in-file-manager (span.name.icon.icon-file-text) -3:30.1.0 core:save (atom-text-editor.editor.is-focused) -3:22.2.0 haskell-ghc-mod:go-to-declaration (atom-text-editor.editor.is-focused) 2x -2:53 ide-haskell:prettify-file (atom-text-editor.editor.is-focused) -2:39.2.0 ide-haskell:toggle-output (atom-text-editor.editor.is-focused) -2:34.6.0 ide-haskell-cabal:build (atom-text-editor.editor.is-focused) -2:24.8.0 ide-haskell-cabal:test (atom-text-editor.editor.is-focused) -2:18.5.0 haskell-ghc-mod:check-file (atom-text-editor.editor.is-focused) -2:14.6.0 haskell-ghc-mod:lint-file (atom-text-editor.editor.is-focused) -2:03.4.0 ide-haskell:prettify-file (atom-text-editor.editor.is-focused) -1:53.1.0 haskell-ghc-mod:lint-file (atom-text-editor.editor.is-focused) 2x -0:59.2.0 haskell-ghc-mod:check-file (atom-text-editor.editor.is-focused) -0:03.8.0 haskell-ghc-mod:shutdown-backend (atom-text-editor.editor.is-focused) ``` ### Config ```json {} ``` ### Installed Packages ```coffee # User haskell-ghc-mod, v1.14.5 ide-haskell, v1.6.5 ide-haskell-cabal, v1.4.0 ide-haskell-repl, v0.0.23 language-haskell, v1.7.16 # Dev No dev packages ``` Regards, Balraj Singh

4 7

New Haddock
by Dominic Steinitz 06 Jun '16

06 Jun '16

I couldn’t find an announcement of the new version of Haddock. You can now document your libraries even more beautifully. For example, > -- \[ > -- f(k;n,p) = \Pr(X = k) = \binom n k p^k(1-p)^{n-k} > -- \] will render as https://hackage.haskell.org/package/random-fu-0.2.7.0/docs/Data-Random-Dist… <https://hackage.haskell.org/package/random-fu-0.2.7.0/docs/Data-Random-Dist…> Also don’t forget you can put really nice diagrams in your documentation e.g. http://hackage.haskell.org/package/diagrams-contrib-1.3.0.7/docs/Diagrams-E… <http://hackage.haskell.org/package/diagrams-contrib-1.3.0.7/docs/Diagrams-E…> and http://hackage.haskell.org/package/diagrams-contrib-1.3.0.7/docs/Diagrams-T… <http://hackage.haskell.org/package/diagrams-contrib-1.3.0.7/docs/Diagrams-T…>. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.wordpress.com

1 0

New version of itself
by martin 06 Jun '16

06 Jun '16

Hello all, I find myself frequentlly writing types like this data Logger a l = Lgr { runLogger :: a -> Log l -> (Log l, Logger a l) } The purpose is to give a logger a chance to carry an internal state. It could e.g. choose to log only every n invocations. To do this it must keep track of how many times it has been called. I want to leave such things private to the Logger. (1) I know that this is not an unusal thing to do, but it has an OO feel to it. Is there a more functional alternative to it. Should I just not worry? (2) I can write a combinator which creates a Logger from a list of Loggers. Since each Logger potentially returns a new version of itself, I must always re-assemble the combined logger from all the returned new versions. I am worried that this is a costly operation, particularly when most Loggers just return themselves unaltered. I don't have any hard numbers about the performance penalty though. These Loggers are used in a discrete-event-simulation and they will get called many times (once for each event), but only occastionally actually write to the Log.

6 9

haskell-ide-engine versus hsdev (and Debuggers)
by Leonard Janke 06 Jun '16

06 Jun '16

Hello, I am new to Haskell and thinking of contributing to the IDE efforts. I've noticed two projects which aim to provide a "service" that editors and IDEs can call to help present useful information to programmers. I am wondering how these projects differ and why they are separate efforts since they seem to have very similar end goals? Another thing that I am wondering is if either of these two projects aims to provide debugger support and what the general state of debuggers for Haskell is? I've seen a project for a Haskell remote debugger which looks it was ghci/interpreter based and was being used by Eclipse and IntelliJ. It didn't work when I tried it, however, and I am not sure that the project is still active. It also looks like ghc only recently began adding support for debugging compiled Haskell and that initial efforts may be to get things working with gdb or lldb. Am I correctly understanding the current landscape as far as Haskell debuggers go? Thanks! Leonard

2 1

Final CFP: 4th ACM SIGPLAN International Workshop on Functional Art, Music, Modelling and Design
by Michael Sperber 05 Jun '16

05 Jun '16

4th ACM SIGPLAN International Workshop on Functional Art, Music, Modelling and Design http://functional-art.org/2016/ Co-located with ICFP Nara, Japan, 24 September, 2016 Key Dates: Submission deadline - June 24 Author Notification - 15 July Camera Ready - 31 July Workshop - September 24, 2016 We welcome submissions from academic, professional, and independent programmers and artists. Final Call for Papers, Demos, *and* Performances The ACM SIGPLAN International Workshop on Functional Art, Music, Modelling and Design (FARM) gathers together people who are harnessing functional techniques in the pursuit of creativity and expression. Functional Programming has emerged as a mainstream software development paradigm, and its artistic and creative use is booming. A growing number of software toolkits, frameworks and environments for art, music and design now employ functional programming languages and techniques. FARM is a forum for exploration and critical evaluation of these developments, for example to consider potential benefits of greater consistency, tersity, and closer mapping to a problem domain. FARM encourages submissions from across art, craft and design, including textiles, visual art, music, 3D sculpture, animation, GUIs, video games, 3D printing and architectural models, choreography, poetry, and even VLSI layouts, GPU configurations, or mechanical engineering designs. Theoretical foundations, language design, implementation issues, and applications in industry or the arts are all within the scope of the workshop. The language used need not be purely functional ("mostly functional" is fine), and may be manifested as a domain specific language or tool. Moreover, submissions focusing on questions or issues about the use of functional programming are within the scope. Submit at : https://easychair.org/conferences/?conf=farm2016

1 0

Strange type error with -XTypeApplications
by Mitchell Rosen 05 Jun '16

05 Jun '16

This program: * {-# LANGUAGE TypeApplications #-}* * main = print (fromDynamic @Int undefined)* produces this error message: * foo.hs:3:15: error:* * • Cannot apply expression of type ‘t0’* * to a visible type argument ‘Int’* * • In the first argument of ‘print’, namely* * ‘(fromDynamic @Int undefined)’* * In the expression: print (fromDynamic @Int undefined)* * In an equation for ‘main’:* * main = print (fromDynamic @Int undefined)* However, I'd expect it to be "Not in scope: fromDynamic"

1 0

Accumulating and threading output of functions
by martin 05 Jun '16

05 Jun '16

Hello all, I have a number of functions, whose type is something like this: f:: a -> b -> (b, c) i.e. it returns a modified b and an additional c. Now I want to write a combinator, which assembles a list of such functions into a single one. This combinator will have to thread the bs from one function to the next and accumulate the cs into a single c. While I was able to write this using a fold, I am not happy with it (my first attempt had a bad error in it, which is always a bad sign). Are you aware of any idioms, how to do such things on the beaten track?

4 3

announce: arithmoi 0.4.2.0
by Carter Schonwald 04 Jun '16

04 Jun '16

It is with great pleasure that the arithmoi maintainers (andrew lelechenko and myself) would like to share the 0.4.2.0 release with the haskell community. This release https://hackage.haskell.org/package/arithmoi-0.4.2.0 includes a multiplicatively infinite (but addititively finite) increase in test coverage and correspondingly every known bug in arithmoi has been fixed (so theres no known crashing/faulting bugs, and all tested code gives mathematically correct answers) I would especially like to thank Andrew Lelechenko for becoming a fellow maintainer, his incredibly meticulous, clean, thorough engineering is really what made this release possible and excellent. this should treated as a stable library version release.

1 0

Month in Haskell Mode May 2016
by Gracjan Polak 04 Jun '16

04 Jun '16

Hi, Month in Haskell Mode May 2016 progress report is available: https://github.com/haskell/haskell-mode/wiki/Month-in-Haskell-Mode-May-2016 -- Gracjan

1 0