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Re: [Haskell-cafe] Are casts required?
by Ryan Ingram 06 Jun '11

06 Jun '11

I always forget to reply all. Silly gmail. On Mon, Jun 6, 2011 at 2:07 AM, Ryan Ingram <ryani.spam(a)gmail.com> wrote: > Hi Pat. There aren't any casts in that code. There are type annotations, > but this is different than the idea of a cast like in C. > > For example > ((3 :: Integer) :: Int) > is a compile error. > > What you are seeing is that 3 has the type (forall a. Num a => a); that is, > the literal '3' gets converted by the compiler into > > fromInteger (I# 3#) > > where 3# represents the machine word '3' and I# is the internal constructor > Word# -> Integer. > > class Num a where > ... > fromInteger :: Integer -> a > > So by 'casting', or rather, providing a type annotation, you are specifying > what instance of Num gets the call to 'fromInteger'. > > As to whether you *need* a type annotation: it depends. For example: > foo () = sameId newId 3 > the compiler will infer the type of 'foo' to be > foo :: forall a. IDs a => () -> a > > If you declare foo as a value, though, you run into the dreaded > monomorphism restriction, and you might get a complaint from the compiler > about ambiguity. > foo2 = sameId newId 3 > > > The monomorphism restriction forces values to be values; otherwise consider > this > > > -- the usual 'expensive' computation > fib :: Num a => a -> a > fib 0 = 1 > fib n = fib (n-1) + fib (n-2) > > x = fib 100000 > > What's the type of x? Most generally, it's > x :: Num a => a > > But this means that x will be recalculated every time it's used; the value > can't be saved since x doesn't represent a single value but rather a > separate value for each instance of Num. You are allowed to manually > specify this type, but without it, the compiler says 'You meant this to be a > value!' and forces it to a particular type if it can, or complains about > ambiguity if it can't. As to how it does so, look up the rules for > defaulting and monomorphism in the Haskell report. > > -- ryan > > > > On Mon, Jun 6, 2011 at 12:45 AM, Patrick Browne <patrick.browne(a)dit.ie>wrote: > >> Are casts required to run the code below? >> If so why? >> Thanks, >> Pat >> >> >> -- Idetifiers for objects >> class (Integral i) => IDs i where >> startId :: i >> newId :: i -> i >> newId i = succ i >> sameId, notSameId :: i -> i -> Bool >> -- Assertion is not easily expressible in Haskell >> -- notSameId i newId i = True >> sameId i j = i == j >> notSameId i j = not (sameId i j) >> startId = 1 >> >> >> instance IDs Integer where >> >> >> >> -- are casts need here? >> sameId (newId startId::Integer) 3 >> sameId (3::Integer) (4::Integer) >> notSameId (3::Integer) (newId (3::Integer)) >> >> 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 >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> > >

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Are casts required?
by Patrick Browne 06 Jun '11

06 Jun '11

Are casts required to run the code below? If so why? Thanks, Pat -- Idetifiers for objects class (Integral i) => IDs i where startId :: i newId :: i -> i newId i = succ i sameId, notSameId :: i -> i -> Bool -- Assertion is not easily expressible in Haskell -- notSameId i newId i = True sameId i j = i == j notSameId i j = not (sameId i j) startId = 1 instance IDs Integer where -- are casts need here? sameId (newId startId::Integer) 3 sameId (3::Integer) (4::Integer) notSameId (3::Integer) (newId (3::Integer)) 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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ANN: mecha-0.0.5
by Tom Hawkins 06 Jun '11

06 Jun '11

Mecha [1,2,3] is a constructive solid modeling DSL. I haven't worked on Mecha in awhile, so this release just contains some minor cleanup and reorganization. My next step is to build an OpenGL interactive visualization tool, something like a basic CAD window to rotate and zoom around 3D models. What is the easiest way to generate polygon meshes from constructive solid geometry? Marching cubes [4] seems pretty involved. -Tom [1] http://hackage.haskell.org/package/mecha [2] https://github.com/tomahawkins/mecha [3] http://tomahawkins.org/ [4] http://en.wikipedia.org/wiki/Marching_cubes

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lambda abstraction
by Patrick Browne 06 Jun '11

06 Jun '11

Are the following two functions equivalent? (i.e. do they describe the same computation) let add1 a = a + 2 let add2 = \ a -> a + 2 :t add1 add1 :: forall a. (Num a) => a -> a :t add2 add2 :: forall a. (Num a) => a -> a Does Haskell interpreter convert all functions in the form of add1 to the lambda form of add2? Does this lambda form represent the operational semantics of Haskell? How should I translate the type information into English? Thanks Pat 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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OK! I have a Mac with Snow Leopard 10.6.7?, Xcode 3.2.6, Haskell Platform 2011.2.0.1; What are 2or 3 ways so far to get a GUI & graphics?
by KC 06 Jun '11

06 Jun '11

-- -- Regards, KC

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I'm trying to install the Haskell Platform on a Mac and ...
by KC 05 Jun '11

05 Jun '11

I'm trying to install the Haskell Platform on a Mac and I've already installed Xcode 3.2.6 but the platform says that the tools are not installed. Do I need to reboot? -- -- Regards, KC

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Subcategories on Hackage
by Tillmann Vogt 05 Jun '11

05 Jun '11

Hi, There are some categories on Hackage that have become so large that it is hard to find something, i.e. Data(414 packages) and Graphics (191). Thats why I suggest to use subcategories separated from the category with a dot. To show that this makes sense I made subcategories for graphics libraries at the end of this email. Whatever happens to hackage2 this would be an immediate improvement. How ------ I would volunteer for the manual categorization and let the community look over it. I could upload the changes with a script but the version number has to increase even if only the category has changed. I also don't want to be responsible for a massive spike in the upload statistics. Shouldn't the cabal file be excluded from the versioning policy? => It is allowed to upload a library with the same version number if only the cabal file has changed. One should write a notifiaction mail to all owners to reply if they don't agree. Then after a week executing the script that applies the changes. Categories for Graphics: Graphics.2d bacteria program: braindead utility to compose Xinerama backgrounds barchart library and program: Creating Bar Charts in Haskell chalkboard library and programs: Combinators for building and processing 2D images. chalkboard-viewer library: OpenGL based viewer for chalkboard rendered images. Chart library: A library for generating 2D Charts and Plots dia-base library: An EDSL for teaching Haskell with diagrams - data types dia-functions library: An EDSL for teaching Haskell with diagrams - functions diagrams library: Embedded domain-specific language for declarative vector graphics diagrams-cairo library: Cairo backend for diagrams drawing EDSL diagrams-core library: Core libraries for diagrams EDSL diagrams-lib library: Embedded domain-specific language for declarative graphics explore program: Experimental Plot data Reconstructor funcmp library: Functional MetaPost gloss library: Painless 2D vector graphics, animations and simulations. gloss-examples programs: Examples using the gloss library GoogleChart library: Generate web-based charts using the Google Chart API graphics-drawingcombinators library: A functional interface to 2D drawing in OpenGL haha library and program: A simple library for creating animated ascii art on ANSI terminals. HDRUtils library: Utilities for reading, manipulating, and writing HDR images hevolisa program: Genetic Mona Lisa problem in Haskell hevolisa-dph program: Genetic Mona Lisa problem in Haskell - using Data Parallel Haskell Hieroglyph library: Purely functional 2D graphics for visualization. HPlot library and program: A minimal monadic PLplot interface for Haskell hs-captcha library: Generate images suitable for use as CAPTCHAs in online web-form security. hs-gchart library: Haskell wrapper for the Google Chart API hsparklines library: Sparklines for Haskell internetmarke program: Shell command for constructing custom stamps for German Post plot library: A plotting library, exportable as eps/pdf/svg/png or renderable with gtk plot-gtk library: GTK plots and interaction with GHCi printxosd program: Simple tool to display some text on an on-screen display scaleimage program: Scale an image to a new geometry testpattern program: Display a monitor test pattern wumpus-basic library: Basic objects and system code built on Wumpus-Core. wumpus-core library: Pure Haskell PostScript and SVG generation. wumpus-drawing library: High-level drawing objects built on Wumpus-Basic. wumpus-microprint library: Microprints - "greek-text" pictures. wumpus-tree library: Drawing trees zsh-battery program: Ascii bars representing battery status Graphics.3d Attrac program: Visualisation of Strange Attractors in 3-Dimensions cal3d library: Haskell binding to the Cal3D animation library. cal3d-examples programs: Examples for the Cal3d animation library. cal3d-opengl library: OpenGL rendering for the Cal3D animation library FieldTrip library: Functional 3D gnuplot library and program: 2D and 3D plots using gnuplot HGL library: A simple graphics library based on X11 or Win32 hgl-example program: Various animations generated using HGL IcoGrid library: Library for generating grids of hexagons and pentagons mapped to a sphere. nymphaea program: An interactive GUI for manipulating L-systems reactive-fieldtrip library: Connect Reactive and FieldTrip reactive-glut library: Connects Reactive and GLUT Graphics.Fractal fractal program: Draw Newton, Julia and Mandelbrot fractals gmndl program: Mandelbrot Set explorer using GTK hfractal program: OpenGL fractal renderer mandulia program: A zooming visualisation of the Mandelbrot Set as many Julia Sets. Graphics.Raytracing glintcollider program: A simple ray tracer in an early stage of development. glome-hs library and program: ray tracer GlomeTrace library: Ray Tracing Library GlomeVec library: Simple 3D vector library HRay program: Haskell raytracer jort program: JP's own ray tracer Graphics.Layout graph-rewriting-layout library: Force-directed node placement intended for incremental graph drawing pango library: Binding to the Pango text rendering engine. Graphics.Algorithm triangulation library: triangulation of polygons splines library: B-Splines, other splines, and NURBS. Graphics.RasterFormats AC-PPM library: Trivial package for writing PPM images. bitmap library: A library for handling and manipulating bitmaps. bitmap-opengl library: OpenGL support for Data.Bitmap. exif library: A Haskell binding to a subset of libexif fig library: Manipulation of FIG files graphicsFormats library: Classes for renderable objects. hsmagick library: FFI bindings for the GraphicsMagick library Imlib library jpeg library: A library for decoding JPEG files written in pure Haskell pgm library: Pure Haskell implementation of PGM image format SDL-image library: Binding to libSDL_image stb-image library: A wrapper around Sean Barrett's JPEG/PNG decoder tga library: Reading and writing of tga image files Graphics.VectorFormats cairo library: Binding to the Cairo library. craftwerk library and programs: 2D graphics library with integrated TikZ output. craftwerk-cairo library: Cairo backend for Craftwerk. craftwerk-gtk library and program: Gtk UI for Craftwerk. HPDF library: Generation of PDF documents hps library: Haskell Postscript hps-cairo library: Cairo rendering for the haskell postscript library HsHaruPDF library: Haskell binding to libharu (http://libharu.sourceforge.net/) poppler library: Binding to the Poppler. svgcairo library: Binding to the libsvg-cairo library. SVGPath library: Parsing the path command from SVG svgutils library and program: Helper functions for dealing with SVG files Graphics.3dFormats collada-output library and program: Generate animated 3d objects in COLLADA collada-types library: data exchange between graphic applications graphics-formats-collada library: Load 3D geometry in the COLLADA format obj library: Reads and writes obj models. Graphics.Engine (OpenGL and libraries that make it easier to use OpenGL) GLURaw library: A raw binding for the OpenGL graphics system GLUT library: A binding for the OpenGL Utility Toolkit GLFW library: A Haskell binding for GLFW GLFW-b library: GLFW bindings GLFW-b-demo program: GLFW-b test\/example\/demo GLFW-OGL library: A binding for GLFW (OGL) GPipe library: A functional graphics API for programmable GPUs GPipe-Collada library: Load GPipe meshes from Collada files GPipe-Examples programs: Examples for the GPipes package GPipe-TextureLoad library: Load GPipe textures from filesystem hogre library: Haskell binding to a subset of OGRE hogre-examples programs: Examples for using Hogre. haskgame library: Haskell game library. IrrHaskell library: Haskell FRP binding to the Irrlicht game engine. lambdacube-bullet program: Example for combining LambdaCube and Bullet lambdacube-engine library: 3D rendering engine entirely written in Haskell lambdacube-examples programs: Examples for LambdaCube nehe-tuts programs: Port of the NeHe OpenGL tutorials to Haskell. OGL library: A context aware binding for the OpenGL graphics system OpenGL library: A binding for the OpenGL graphics system OpenGLCheck library: Quickcheck instances for various data structures. OpenGLRaw library: A raw binding for the OpenGL graphics system OpenGLRaw21 library: The intersection of OpenGL 2.1 and OpenGL 3.1 Core rsagl library: The RogueStar Animation and Graphics Library scenegraph library: Scene Graph Graphics.Fonts font-opengl-basic4x6 library and program: Basic4x6 font for OpenGL freetype2 library and program: Haskell binding for FreeType 2 library FTGL library: Portable TrueType font rendering for OpenGL using the Freetype2 library SDL-ttf library: Binding to libSDL_ttf SFont library: SFont SDL Bitmap Fonts stb-truetype library: A wrapper around Sean Barrett's TrueType rasterizer library. SVGFonts library and program: Fonts from the SVG-Font format Graphics.OSspecific GLHUI library: Open OpenGL context windows in X11 with libX11 ige-mac-integration library: Bindings for the Gtk/OS X integration library. minimung program: Shows how to run grabber on Mac OS X Win32 library: A binding to part of the Win32 library X11 library: A binding to the X11 graphics library X11-extras library: Missing bindings to the X11 graphics library X11-rm library: A binding to the resource management functions missing from X11. X11-xdamage library: A binding to the Xdamage X11 extension library X11-xfixes library: A binding to the Xfixes X11 extension library X11-xft library: Bindings to the Xft, X Free Type interface library, and some Xrender parts x11-xim library: A binding to the xim of X11 graphics library X11-xshape library: A binding to the Xshape X11 extension library Xauth library: A binding to the X11 authentication library xhb library: X Haskell Bindings xosd library: A binding to the X on-screen display Graphics.UserInterfaces glade library: Binding to the glade library. gtk library: Binding to the Gtk+ graphical user interface library. gtk-serialized-event library: GTK+ Serialized event. gtkglext library: Binding to the GTK+ OpenGL Extension gtkimageview library: Binding to the GtkImageView library. gtksourceview2 library: Binding to the GtkSourceView library. lui library: Purely FunctionaL User Interface soegtk library: GUI functions as used in the book "The Haskell School of Expression". Graphics.Vector AC-Vector library: Efficient geometric vectors and transformations. AC-Vector-Fancy library: Fancy type-system stuff for AC-Vector Vec-OpenGLRaw library: Instances and functions to interoperate Vec and OpenGL. Vec-Transform library: Extends the Vec package with some 4x4 transform matrices vect library: A low-dimensional linear algebra library, tailored to computer graphics. vect-opengl library: OpenGL support for the `vect' low-dimensional linear algebra library. Graphics.Visualization graphviz library and program: Graphviz bindings for Haskell. hubigraph library: A haskell wrap for Ubigraph splot program: A tool for visualizing the lifecycle of many concurrent multi-staged processes. timeplot program: A tool for visualizing time series from log files. Games HTicTacToe program: An SDL tic-tac-toe game. Graphics (not subcategorized yet) AC-Colour library: Efficient RGB colour types. AC-EasyRaster-GTK library: GTK+ pixel plotting. assimp library: The Assimp asset import library Chitra program: A platform independent mechanism to render graphics using vnc. colour library: A model for human colour/color perception CV library: OpenCV based machine vision library cv-combinators library and programs: Functional Combinators for Computer Vision derivation-trees library: Typeset Derivation Trees via MetaPost gd library: A Haskell binding to a subset of the GD graphics library ghci-diagrams library: Display simple diagrams from ghci graph-rewriting-gl library: OpenGL interface for interactive port graph rewriting HOpenCV library and program: A binding for the OpenCV computer vision library IFS library and program: Iterated Function System generation for Haskell Noise library: A Haskell coherent noise generator based on libnoise ObjectIO library OpenCLRaw library: The OpenCL Standard for heterogenous data-parallel computing OpenVG library: OpenVG (ShivaVG-0.2.1) binding OpenVGRaw library: Raw binding to OpenVG (ShivaVG-0.2.1 implementation). probability library: Probabilistic Functional Programming SGdemo program: An example of using the SG and OpenGL libraries SDL library: Binding to libSDL SDL-gfx library: Binding to libSDL_gfx SDL-mixer library: Binding to libSDL_mixer SDL-mpeg library: Binding to the SMPEG library smallpt-hs program: A Haskell port of the smallpt path tracer. Sprig library: Binding to Sprig treemap-html library: Generates HTML for Data.Tree as TreeMap treemap-html-tools library and programs: Treemap related commands for producing foldable TreeMap HTML. vte library: Binding to the VTE library. webkit library: Binding to the Webkit library. wordcloud library: Library for generating word/tag clouds.

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Re: [Haskell-cafe] ANN: dtd-types 0.3.0.1
by Yitzchak Gale 05 Jun '11

05 Jun '11

The dtd-types[1] package provides types for processing XML DTDs in Haskell. These types are intended to be compatible with and extend the set of types provided by John Millikin's xml-types package[2]. This version, 0.3.0.1, was released in support of the dtd-text package[3]. It includes some major changes to some of the names, as well as some bug fixes. In particular, all names relating to XML attributes which used to begin with the prefix "Attr" or "attr" have been changed to begin with "att" or "Att" instead. The "EntityContent" type has been renamed to "EntityValue". These are much more consistent with nomenclature in the XML specs. At this point, the dtd-types package should start becoming a bit more stable, since it is now being used by other packages. Enjoy, Yitz [1] http://hackage.haskell.org/package/dtd-types/ [2] http://hackage.haskell.org/package/xml-types/ [3] http://hackage.haskell.org/package/dtd-text/

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Fwd: Abnormal behaviors when Using ghci
by 吴兴博 05 Jun '11

05 Jun '11

---------- Forwarded message ---------- From: 吴兴博 <wuxb45(a)gmail.com> Date: 2011/6/5 Subject: Abnormal behaviors when Using ghci To: cvs-ghc(a)haskell.org 1) I'm using Haskell platform 2011.2 on windows (7). Every several days, ghci will crash with no messages. even when I'm just typing with text buffer, without an 'enter'. I got nothing after the crash, not even an exception code, don't even mention the core-dump. Should I report bugs with nothing to give, only "it crashes."? I think I should be careful with sending messages. 2) do that: open ghci. > :set -fbreak-on-exception > :trace [undefined] then you catch a _exception > :print _exception Then it prints a chaos... that's because the printing of the exception contains too many white-spaces because of indent. I think this can be some kind of malformed features. since It isn't a bug, what 'type' should the problem be? :-) regards! -- ---------------- 吴兴博 Wu Xingbo

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Re: [Haskell-cafe] [iteratee] how to do nothing .. properly
by John Lato 05 Jun '11

05 Jun '11

Hi Sergey, I can't explain this; maybe it's a bug in enumWith? I'll look into it. Thanks, John > Message: 20 Date: Thu, 2 Jun 2011 02:46:32 +0400 > From: Sergey Mironov <ierton(a)gmail.com> > Subject: [Haskell-cafe] [iteratee] how to do nothing .. properly > To: haskell-cafe(a)haskell.org > Message-ID: <BANLkTimMFRWgH9Nopt-eua%2BL7jQcGq%2Bu%3Dg(a)mail.gmail.com> > Content-Type: text/plain; charset=ISO-8859-1 > > Hi. Would anybody explain a situation with iter6 and iter7 below? > Strange thing - first one consumes no intput, while second consumes it > all, while all the difference is peek which should do no processing > (just copy next item in stream and return to user). > What I am trying to do - is to write an iteratee consuing no input, > but returning a constant I give to it. I thought (return a) should do > it, but it seems I was wrong as return actually consumes all unparsed > stream. iter6 experience tells me that (peek>>return a) is what I > need, but it's completely confusing and not what I expected. > > Thanks, > Sergey > > import Data.Iteratee as I > import Data.Iteratee.IO > import Control.Monad > import Control.Exception > import Data.ByteString > import Data.Char > import Data.String > > -- countBytes :: (..., Num b) => Iteratee s m a -> Iteratee s m (a, b) > countBytes i = enumWith i I.length > > iter6 = do > h <- countBytes $ (peek >> return 0) > s <- I.stream2list > return (h,s) > > iter7 = do > h <- countBytes $ (return 0) > s <- I.stream2list > return (h,s) > > print6 = enumPure1Chunk [1..10] (iter6) >>= run >>= print > print7 = enumPure1Chunk [1..10] (iter7) >>= run >>= print > > > Here is example ghci session > > *Main> print6 > ((0,0),[1,2,3,4,5,6,7,8,9,10]) > -- read 0 items, returns 0 > *Main> print7 > ((0,10),[]) > -- read 10 items (???) returns 0 > *Main> > > > > ------------------------------ > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe > > > End of Haskell-Cafe Digest, Vol 94, Issue 3 > ******************************************* >

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