October 2010 - Haskell-Cafe

Re: [Haskell-cafe] If Python now has a good email library; how challenging is it to call Python from Haskell?
by Brandon Moore 27 Oct '10

27 Oct '10

On Oct 27, 2010, at 12:43 PM, caseyh(a)istar.ca wrote: > :) I will point out that "Python Haskell Interface" has an excellent axiom. Unfortunately, my attempt to write a nice wrapper around the Python FFI foundered years ago chasing segfaults. It doesn't seem like it should be too hard, if you get the reference counting right - and tie everything to the GIL (ick).

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Where has GDK.GC gone?
by Andrew Coppin 27 Oct '10

27 Oct '10

Today I noticed a small but interesting fact: Under Gtk2hs 0.10.x, the module Graphics.UI.Gtk re-exports (amoung countless others) the module Graphics.UI.Gtk.Gdk.GC. However, under Gtk2hs 0.11.x, it does not. After downloading the darcs repo (with took forever, by the way), I discovered that the requisit line still exists in the source code, but it has been commented out. My repeated attempts to force Darcs to tell me exactly which patch did this resulted only in Darcs locking up again and again. (I'm quite surprised at that. Usually all Darcs operations are instantaneous. I guess the local repo is corrupt somehow or something...) So anyway, what I'd like to know is... was this alteration intensional? Or was it just an oversight? PS. The link on the website that says "browse the darcs repo online"? Apache just returns 404 at me. This is not particularly helpful.

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Haskell and a complete mail client lib?
by Günther Schmidt 27 Oct '10

27 Oct '10

Hi all, do we Haskellers have a complete Mail client library? One that goes beyond an unstructured byte string? Günther

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Pretty-printer for Text
by Ivan Lazar Miljenovic 27 Oct '10

27 Oct '10

I'm currently working on a pretty-printer for lazy text [1] values, basing the API on the wl-pprint [2] package. [1]: http://hackage.haskell.org/package/text [2]: http://hackage.haskell.org/package/wl-pprint In terms of API decisions, there are a few things I'm not sure of and am wondering what other people would prefer: * Should the SimpleDoc type still be exported? Or should the rendering functions just return a Builder or lazy Text value? * Is the Pretty class wanted/needed? If so, should the individual combinators (int, bool, etc.) be kept or just use "pretty" for everything? * Should String values be catered for or just have everything be Text-based? -- Ivan Lazar Miljenovic Ivan.Miljenovic(a)gmail.com IvanMiljenovic.wordpress.com

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ANN: timeplot-0.2.1, a tool for visualizing time series from log files.
by Eugene Kirpichov 27 Oct '10

27 Oct '10

Hi cafe, I'm pleased to announce timeplot-0.2.1. http://hackage.haskell.org/package/timeplot This is a tool for visualizing time series from log files. I'm myself using it for diagnosing performance of distributed systems: I aggregate their logs and plot various things, such as the number of tasks executing on each machine of the cluster, or quantiles of database query times, etc. See pretty pictures on haskellwiki: http://www.haskell.org/haskellwiki/Timeplot This version has several changes, which together raised the program's usefulness for me tremendously: - The program now builds and works on Windows! You just need gtk2hs. I got rid of strptime and pcre dependencies (strptime is built from bundled and patched source, and I use regex-tdfa by Chris Kuklewicz). - Support for millisecond precision on charts (thanks to the new 0.14 version of Tim Docker's excellent Chart library) - Support for millisecond precision in input (because I re-did strptime to compile from scratch with support for the %OS pattern, which recognizes fractional seconds) - Support for selecting a range of the input (however, non-interactively) with "-fromTime/-toTime" - Support for "duration" plots: given an event track (where events of something beginning or ending are recorded), you can produce all kinds of plots over the durations of these events. - Support for colored "status" plots: now event tracks represent not purely the presence or absence of an active event, but an event track can be colored, representing several states of a subsystem or subprocess. Please use the program and provide feedback :) I have a hope that it could become a reasonably widely used tool for the kinds of tasks that I use it for. -- Eugene Kirpichov Senior Software Engineer, Grid Dynamics http://www.griddynamics.com/

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cross-platform compile
by Hong Yang 27 Oct '10

27 Oct '10

Just curious if Haskell can or will generate cross-platform executable code, e.g., generate code for Linux from a Windows machine. Thanks, Hong

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ANN: Chart v0.14
by Tim Docker 27 Oct '10

27 Oct '10

I'm pleased to announce v0.14 of the haskell chart library. This is a library for drawing 2D data plots. It's features include + Use of the cairo graphics engine, supporting a variety of output types: ps, pdf, png, and gtk windows. + A variety of plot types, including: points, lines, error bars, candlesticks, bar charts and pie charts. + Strong typing. Charts are parameterized by the types of their coordinates. One benefit of this is that labels etc are automatically generated appropriately for the type of the data. Currently axis types include: Double, Int, Log, LocalTime, and Indexed. + (some) support for interactivity. Charts support dynamic resizing, and mapping from device coordinates back to source values. The library is available on hackage. Additional information including details of the mailing list can be found here: http://dockerz.net/software/chart.html Thanks to Malcolm Wallace, Eugene Kirpichov, and Matt Brown for their contributions to this release. Tim Docker ---------------------------------------------------------------------- New features in v0.14 --------------------- * Plot Type: AreaSpots4D Spots with varying area and colour * Plot Type: CandleStick charts A specific type of plot often used in financial markets for stock price series. * Multiline text in Annotation Plots with flexible control over the anchoring. * Picking. The library now contains logic required to map device coordinates back to input elements. This facilitates interactivity. See tests/TestPicking.hs. * Multiple Layers of axis labels This is currently used by the LocalTime axis to show an additional set of context labels - these show the next sensible granularity of time enclosing the more detailed labels and ticks. * Avoid overlapping axis labels The axis rendering code now skips labels where there would be overlaps. This is done dynamically as the chart is rendered. * Code refactor Plots and axes have been split into separate file hierarchies, with one file per type. This makes it easier to understand, and (hopefully) makes it clearer how to add new plot types.

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Help me TH code.
by Andy Stewart 27 Oct '10

27 Oct '10

Hi all, I want use TH write some function like below: data DataType = StringT | IntT | CharT parse :: [(String,DataType)] -> (TypeA, TypeB, ... TypeN) Example: parse [("string", StringT), ("001", IntT), ("c", CharT)] will return: ("string", 001, 'c') So how to use TH write 'parse' function? Thanks! -- Andy

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Understanding Iteratees
by Arnaud Bailly 27 Oct '10

27 Oct '10

Hello, I am trying to wrap my head around the concept of Iteratee reading the article by John Lato in Monad Reader issue 16 (http://themonadreader.files.wordpress.com/2010/05/issue16.pdf) I followed the "advice" on page 34: "I have frequently heard reports from Haskellers (including highly-talented and experienced users) that the only way they could understand enumeration-based I/O was by re-implementing it themselves." and so reimplemented this code in Java which is, for better and worse, my current professional language (and there really is no point in writing my own 50th iteratee code...). I have a question about iteratees composition and their behaviour. I tried to use the throbber code to display progress while writing a file, without using enumeratees which are introduced later on in the article, but failed. I can bind the two iteratees together, but the writer iteratee consumes the stream of characters to write before handing over the control to the throbber iteratee which has nothing to count. Did I miss something ? Thanks in advance, Arnaud

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HDF5
by Tim Sears 26 Oct '10

26 Oct '10

Does anybody know of any utilities in haskell for reading and writing HDF5 files? Other number crunchy formats? Thanks.--Tim

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