- Haskell-Cafe - Haskell.org

Hacking GHC's Stack for Fun and Profit (featuring The Glorious Haskell Debugger v0.0.1 Pre-alpha)
by Tim C. Schroeder 20 Jan '14

20 Jan '14

Hello, I have developed various profiling and debugging tools in the past, but haven't done any work in that direction for GHC compiled Haskell programs. I thought a good start might be to write a document detailing how the call stack works in GHC, and also write a basic debugger stack trace tool. Here: https://github.com/blitzcode/ghc-stack I hope this is helpful to people trying to pin down crashes, and people interested in working on debugging / profiling tools. I'd also really appreciate if somebody with more GHC / RTS knowledge than me would have a look and see if I got things right. Cheers, Tim

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Re: [Haskell-cafe] different behaviours with or without putStrLn
by Corentin Dupont 20 Jan '14

20 Jan '14

One question: Since it works with putStrLn, can I simulate the behaviour of putStrLn without actually... printing anything? As a workaround... On Mon, Jan 13, 2014 at 12:40 AM, Corentin Dupont <corentin.dupont(a)gmail.com > wrote: > I doesn't seems to be easy, either with deepseq-th or deepseq-generic... > With deepseq-generic, the derivation of Generic doesn't work because I'm > using a GATD. > It says *"NewVar must be a vanilla data constructor"*. > > For deepseq-th, I have this error: > > *deriveNFData: 'forall' not supported in constructor declaration* > I have some complex data constructor... > > > So it looks like both deepseq-th and deepseq-generic are out of the game > :(( > > > > > On Mon, Jan 13, 2014 at 12:08 AM, Erik de Castro Lopo < > mle%2Bhs(a)mega-nerd.com> wrote: > >> James ‘Twey’ Kay wrote: >> >> > You can (probably) automatically derive it via Template Haskell using >> > the deepseq-th package: >> > >> > {-# LANGUAGE TemplateHaskell #-} >> > import Control.DeepSeq.TH >> > >> > data MyState = ... >> > >> > $(deriveNFData ''MyState) >> >> In most cases where you think >> >> You should probably try the deepseq-generics package before you try >> deepseq-th. >> >> The generics version was suggested to me by the author of the TH version, >> Herbert Valerio Riedel. It seems to be just as fast as the TH version and >> doesn't require TH. >> >> Cheers, >> Erik >> -- >> ---------------------------------------------------------------------- >> Erik de Castro Lopo >> http://www.mega-nerd.com/ >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

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Combining databases from packages installed with cabal install
by Marco Túlio Pimenta Gontijo 20 Jan '14

20 Jan '14

Hi. I'm configuring haddock via cabal install (see [0]) to build the hoogle database. The database is being installed in ~/.cabal/share/doc/$package-$version/html/$package.txt, but is not being combined with the default database. That is, if right after the installation I try to search with the hoogle command for some a function, it will not work. I wrote the following script, which I called cabal-install: #!/bin/sh set -e set -x cabal \ install \ --enable-documentation \ --enable-library-profiling \ --haddock-hyperlink-source \ --haddock-hoogle \ --haddock-html \ "$@" cd ~/.cabal/share/hoogle-4.2.13/databases/ for file in ~/.cabal/share/doc/*/html/*.txt do hoo=`echo $file | sed 's/.txt$/.hoo/;s#.*/##'` if [ ! -f $hoo ] then hoogle convert $file $hoo || true hoogle combine default.hoo $hoo -o /tmp/cabal-install-$$.hoo mv /tmp/cabal-install-$$.hoo default.hoo fi done Basically, it searches for .txt hoogle databases installed that were not combined yet with the default database, and combines them. I think it would be good if this was the default behaviour of cabal install when called with --haddock-hoogle. Is this a bug? Greetings. 0: http://hackage.haskell.org/trac/hackage/ticket/517 -- marcot http://marcot.eti.br/

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ANN: unsafely, Flexible access control for unsafe operations and instances
by Hiromi ISHII 19 Jan '14

19 Jan '14

Yesterday, I uploaded the library `unsafely` to Hackage: http://hackage.haskell.org/package/unsafely This package provides you the functionality for access control for unsafe operations and instances. This purpose is somewhat similar to GHC's `NullaryTypeClasses`[^1] extension, but permits more flexible access control. With this package, you can tag functions and type-class instances as *unsafe* in type constraint. This library is useful when: * You want to restrict the access to *unsafe* operations by type constraint * You have to provide some *unsafe* type-instances for practical reasons. For example, when writing computer algebra system with type-classes, `Double` type doesn't even form a semi ring, but we need the instance `Semiring Double` if we want to combine the symbolic computations and the numerical methods. A simple example: ```haskell {-# LANGUAGE FlexibleContexts, FlexibleInstances, RankNTypes #-} {-# LANGUAGE UndecidableInstances #-} module Main where import Data.Constraint.Unsafely import Data.IORef import Data.Proxy import System.IO.Unsafe saferUnsafePerformIO :: Unsafely IO => IO a -> a saferUnsafePerformIO = unsafePerformIO global :: Unsafely IO => IORef Int global = saferUnsafePerformIO $ newIORef 0 unsafelyIO :: (Unsafely IO => a) -> a unsafelyIO = unsafely (Proxy :: Proxy IO) main :: IO () main = do unsafelyIO $ readIORef global -- | uncommenting following line causes type-error! -- readIORef global return () ``` For more detail, please read Haddock[^2]. [^1]: https://ghc.haskell.org/trac/ghc/ticket/7642 [^2]: http://hackage.haskell.org/package/unsafely-0.1.0.0.1/docs/Data-Constraint-… -- Hiromi ISHII konn.jinro(a)gmail.com

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Help with Binary Serialization
by Joey Eremondi 18 Jan '14

18 Jan '14

I was wondering if somebody could talk me through the default derived format for binary serialization used, either by binary or by cereal. I'm trying to share data between Haskell and another function language (Elm) which also supports algebraic data types, so the conversion of data should be pretty trivial. I'd like to be able to just derive encode and decode in Haskell using either binary/cereal, and then write a parser for the same format in Elm. The trick is, I don't know what that format is. Is there any documentation on it, or if not, is anybody familiar enough with it that they could explain the format to me? Thanks!

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Standard implementation of asynchronous helpers?
by Tristan Seligmann 18 Jan '14

18 Jan '14

I was wondering if a standard implementation of these helpers (or something similar) existed somewhere: startAsync :: IO a -> IO (MVar a) startAsync action = do var <- newEmptyMVar forkIO $ action >>= putMVar var return var wait :: MVar a -> IO a wait = readMVar I've found a few throwaway examples that implement something similar, and I can imagine some improvements already (I guess the MVar should be wrapped, for example, and some higher) but I was unable to find any released library that does something like this. Is it just too trivial for anyone to have bothered? -- mithrandi, i Ainil en-Balandor, a faer Ambar

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Building ghc-7.6.3 under cygwin
by Dmitry Malikov 18 Jan '14

18 Jan '14

Trying to build 7.6.3-x86_64-unknown-linux under cygwin. $ ./configure checking for path to top of build tree... ./configure: line 2121: utils/ghc-pwd/dist-install/build/tmp/ghc-pwd: cannot execute binary file configure: error: cannot determine current directory Not sure it is a libgmp issue, because linking doesn't help: $ ln -s /usr/lib/libgmp.dll.a /usr/lib/libgmp.so.3 Any ideas what is going on and how to fix this?

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Re: [Haskell-cafe] [Haskell] Just started working with Haskell. Need some help
by Henning Thielemann 18 Jan '14

18 Jan '14

moving to Haskell-Cafe ... Am 18.01.2014 18:25, schrieb Pyro Crane: > But, when I try to run a simple script, I keep getting the error : > "*Could not find module XXXXXX*".............. What precisely did you try? > And, now, I've come up against a module/package, which I am unable to > locate in Google. It's missing from my installation, and Google does > not know what it is, or where I can find it > > Is there any way to simply install ALL required packages??? I thought > I already did this, but obviously I missed something $ cabal install wantedpkg should install all dependencies of 'wantedpkg'. If it does not I am interested in how you tried to install 'wantedpkg'.

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ANNOUNCE: Diagrams 1.0
by Brent Yorgey 18 Jan '14

18 Jan '14

The diagrams team is very pleased to announce the 1.0 release of diagrams [1], a framework and embedded domain-specific language for declarative drawing in Haskell. Check out the gallery [2] for some examples of what it can do. Diagrams can be used for a wide range of purposes, from data visualization [3] to illustration [4] to art [5], and diagrams code can be seamlessly embedded in blog posts [6], LaTeX documents [7], and Haddock documentation [8], making it easy to incorporate diagrams into your documents with minimal extra work. [1] http://projects.haskell.org/diagrams [2] http://projects.haskell.org/diagrams/gallery.html [3] http://idontgetoutmuch.wordpress.com/2013/10/23/parking-in-westminster-an-a… [4] https://www.fpcomplete.com/user/edwardk/cellular-automata/part-1 [5] http://mathlesstraveled.com/2013/04/06/stars-of-the-minds-sky-with-diagrams/ [6] http://byorgey.wordpress.com/2012/08/28/creating-documents-with-embedded-di… [7] http://projects.haskell.org/diagrams/doc/latex.html [8] http://byorgey.wordpress.com/2013/03/23/introducing-diagrams-haddock/ What's new ---------- Brent recently gave a talk at the New York Haskell Users' Group [12] presenting the new release. You can find videos of the talk on vimeo: part 1 presents a basic introduction to the library [13], and part 2 talks about mathematical abstraction and DSL design [14]. The slides are also available [15]. [12] http://www.meetup.com/NY-Haskell/ [13] http://vimeo.com/84104226 [14] http://vimeo.com/84249042 [15] http://www.cis.upenn.edu/~byorgey/pub/13-11-25-nyhaskell-diagrams.pdf This release includes a number of significant new features and improvements. Highlights include: - Support for drawing arrows between given points or between diagrams, with many options for customization (tutorial [16], documentation [17], API [18]). [16] http://projects.haskell.org/diagrams/doc/arrow.html [17] http://projects.haskell.org/diagrams/doc/manual.html#arrows [18] http://projects.haskell.org/diagrams/haddock/Diagrams-TwoD-Arrow.html - A new framework for creating custom command-line-driven executables for diagram generation (tutorial [19], API [20]). [19] http://projects.haskell.org/diagrams/doc/cmdline.html [20] http://projects.haskell.org/diagrams/haddock/Diagrams-Backend-CmdLine.html - Offsets of trails and paths, i.e. compute the trail or path lying a constant distance from the given one (documentation [21], API [22]). [21] http://projects.haskell.org/diagrams/doc/manual.html#offsets-of-segments-tr… [22] http://projects.haskell.org/diagrams/haddock/Diagrams-TwoD-Offset.html - A new API, based on Metafont, for constructing cubic splines with control over things like tangents and "tension" (tutorial [23], API [24]). [23] http://projects.haskell.org/diagrams/doc/metafont.html [24] http://projects.haskell.org/diagrams/haddock/Diagrams-TwoD-Path-Metafont.ht… - Tangent and normal vectors of segments and trails (API [25]). [25] http://projects.haskell.org/diagrams/haddock/Diagrams-Tangent.html - Alignment can now be done by trace in addition to envelope (API [26]). [26] http://projects.haskell.org/diagrams/haddock/Diagrams-TwoD-Align.html - The lens [27] package is now used consistently for record fields throughout the library (documentation [28]). [27] http://hackage.haskell.org/package/lens [28] http://projects.haskell.org/diagrams/doc/manual.html#faking-optional-named-… - Across-the-board improvements in performance and size of generated files. See the release notes [29] for full details, and the migration guide [30] for help porting your diagrams 0.7 code to work with diagrams 1.0. [29] http://projects.haskell.org/diagrams/releases.html [30] http://www.haskell.org/haskellwiki/Diagrams/Dev/Migrate1.0 Try it out ---------- For the truly impatient: cabal install diagrams Diagrams is supported under GHC 7.4 and 7.6. To get started, read the quick start tutorial [31], which will introduce you to the fundamentals of the framework and provide links for further reading. For those who are less impatient and want to really dig in and use the power features, read the extensive user manual [32]. There is also a growing collection of tutorials [33] on specific topics. [31] http://projects.haskell.org/diagrams/doc/quickstart.html [32] http://projects.haskell.org/diagrams/doc/manual.html [33] http://projects.haskell.org/diagrams/documentation.html Get involved ------------ Diagrams has a friendly and growing community of users and developers. To connect with the community, subscribe to the project mailing list [34], and/or come hang out in the #diagrams IRC channel on freenode.org for help and discussion. Development continues stronger than ever, and there are a wide range of projects available for new contributors of all levels of Haskell skill. Make some diagrams. Fix some bugs [35]. Submit your cool examples for inclusion in the gallery [36] or your cool code for inclusion in the diagrams-contrib [37] package. [34] http://groups.google.com/group/diagrams-discuss [35] http://github.com/diagrams/ [36] http://projects.haskell.org/diagrams/gallery.html [37] http://hackage.haskell.org/package/diagrams%2Dcontrib Happy diagramming! Brought to you by the diagrams team: - Daniel Bergey - Jeff Rosenbluth - Ryan Yates - Brent Yorgey with contributions from: - Jan Bracker - Conal Elliott - Daniil Frumin - Sam Griffin - Niklas Haas - Peter Hall - Claude Heiland-Allen - Deepak Jois - John Lato - Felipe Lessa - Chris Mears - Ian Ross - Carlos Scheidegger - Vilhelm Sjöberg - Michael Sloan - Jim Snavely - Luite Stegeman - Kanchalai Suveepattananont - Michael Thompson - Scott Walck

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Automatic differentiation and dimension types
by Douglas McClean 18 Jan '14

18 Jan '14

Has anyone explored the intersection between automatic differentiation and dimension types (like those in the dimensional package or along the lines of any of the approaches discussed at http://www.haskell.org/haskellwiki/Physical_units)? It's tricky because for ordinary automatic differentiation the types are all the same, but when dimensions get involved that isn't the case, you have to keep dividing by the dimension of the infinitesimal. -Doug McClean

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