March 2009 - Haskell-Cafe

big discussion about Haskell on Reddit
by FFT 15 Mar '09

15 Mar '09

I noticed that on Programming Reddit, where I lurk, there is a big discussion about the disconnect between how much Haskell is advocated there and the number of applications written in it. http://www.reddit.com/r/programming/comments/84sqt/dear_reddit_i_am_seeing_… The difficulty of reasoning about memory and CPU-efficiency in nontrivial programs was suggested as an explanation.

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I can't install hs-plugins beceause of Linker.h
by Yuri Kashnikoff 15 Mar '09

15 Mar '09

Hi! I was trying to install hs-plugins both from sources "$./Setup.lhs ..." and with "$cabal fetch&&cabal install" and both failed. It always reports that Linker.h is missing. I have tried to use --extra-include-dirs with path to ghc-6.10.1 dir and ghc-6.10.1/include dir. Nothing changed. Here is a report from Setup.lhs: Setup.lhs:2:2: Warning: In the use of `defaultUserHooks' (imported from Distribution.Simple): Deprecated: "Use simpleUserHooks or autoconfUserHooks, unless you need Cabal-1.2 compatibility in which case you must stick with defaultUserHooks" Warning: defaultUserHooks in Setup script is deprecated. Configuring plugins-1.4.0... Warning: This package indirectly depends on multiple versions of the same package. This is highly likely to cause a compile failure. package ghc-6.10.1 requires Cabal-1.6.0.1 package plugins-1.4.0 requires Cabal-1.6.0.2 checking build system type... i386-apple-darwin9.6.0 checking for ghc... ghc checking for value of __GLASGOW_HASKELL__... 610 checking for ghc library directory... /opt/local/lib/ghc-6.10.1/. checking for gcc... gcc checking for C compiler default output file name... a.out checking whether the C compiler works... yes checking whether we are cross compiling... no checking for suffix of executables... checking for suffix of object files... o checking whether we are using the GNU C compiler... yes checking whether gcc accepts -g... yes checking for gcc option to accept ANSI C... none needed checking for arc4random... yes checking for a BSD-compatible install... /usr/bin/install -c configure: creating ./config.status config.status: creating config.mk config.status: creating testsuite/makewith/io/TestIO.conf config.status: creating testsuite/makewith/unsafeio/Unsafe.conf config.status: creating config.h config.status: config.h is unchanged Setup.lhs: Missing dependency on a foreign library: * Missing header file: Linker.h This problem can usually be solved by installing the system package that provides this library (you may need the "-dev" version). If the library is already installed but in a non-standard location then you can use the flags --extra-include-dirs= and --extra-lib-dirs= to specify where it is. -- Yuri S. Kashnikov Novosibirsk State University, Russia 2 Pirogova street 630090, Novosibirsk-90 yuri.kashnikoff(a)gmail.com

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Link errors
by Lingappan, Loganathan 15 Mar '09

15 Mar '09

Hi, If I include import Text.Regex.Posix ((=~)) into a Haskell code, I get the following link error: FindBBUsage.o:fake:(.text+0x44d): undefined reference to `__stginit_regexzmposixzm0zi72zi0zi3_TextziRegexziPosix_' collect2: ld returned 1 exit status Any ideas on how to fix this? I am using GHC version 6.10.1 on Windows XP. Thanks, Logo

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ANNOUNCE: dzen-utils 0.1
by Felipe Lessa 15 Mar '09

15 Mar '09

Hello! I'm please to announce dzen-utils 0.1. I don't feel like it is ready to be released, but let's see how everything goes. :) == WHAT == dzen-utils contains various utilities for creating dzen input strings in a type-safe way using some combinators, including the ability to apply colors locally (instead of applying for everything beyond some point). It can also emulate dbar and gdbar, do automatic padding, and more. == WHY == I don't like to write bash scripts for dzen, and I don't like the way xmobar treats its configuration and its inability to show anything other than text. This package is a short-term solution for my problems. Maybe I'll write xmozen in the future. ;) == WHERE, HOW, etc. == It is in Hackage already, go get it[1]. Please see the documentation of System.Dzen for some small examples. [1] http://hackage.haskell.org/cgi-bin/hackage-scripts/package/dzen-utils Thanks for your time, -- Felipe.

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How to catch error in array index when debugging
by Colin Paul Adams 15 Mar '09

15 Mar '09

I'm getting a runtime failure "Error in array index". This causes ghci to exit. Is there a way to get it to break instead, so I can find out which function is failing? -- Colin Adams Preston Lancashire

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Re: [Haskell-cafe] Default Tuple Orderings
by Martijn van Steenbergen 15 Mar '09

15 Mar '09

Mark Spezzano wrote: > In other words my best guess is that the ordering of tuples is by > comparing the first tuple elements and then the seconds, thirds etc, > until there’s an element less than another. ...until there's an element not equal to the other, yes. It finds the first position at which the two elements in the tuples are unequal and returns the result of comparing those two elements (LT or GT). If there's no such position, then the tuples are equal. See also: http://en.wikipedia.org/wiki/Lexicographical_order HTH, Martijn.

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is there a version of hsffig that builds on a recent versin of haskell?
by Anatoly Yakovenko 15 Mar '09

15 Mar '09

is there a version of hsffig that builds on a recent versin of haskell?

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Default Tuple Orderings
by Mark Spezzano 15 Mar '09

15 Mar '09

Hi, Does anyone know how Haskell’s tuple ordering works? Presumably for some tuple T1 (x1,x2,...xn) and another tuple T2 (y1,y2,...yn) Haskell would compare T1 and T2 as follows: T1 < T2 if: x1 < y1 OR otherwise if x1 == y1 then if x2 < y2 OR otherwise if x2 == y2 then if x3 < y3 OR otherwise etc xn < yn OR otherwise both tuple are equal In other words my best guess is that the ordering of tuples is by comparing the first tuple elements and then the seconds, thirds etc, until there’s an element less than another. Is this reasoning correct? So minimum xs would yield the “smallest” tuple (according to the above rules and if xs is a list of tuples)? Cheers, Mark Spezzano No virus found in this outgoing message. Checked by AVG. Version: 7.5.557 / Virus Database: 270.11.13/2001 - Release Date: 14/03/2009 6:54 AM

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A systematic method for deriving a defintion of foldl using foldr?
by R J 15 Mar '09

15 Mar '09

foldl and foldr are defined as follows: foldr :: (a -> b -> b) -> b -> [a] -> b foldr f e [] = e foldr f e (x : xs) = f x (foldr f e xs) foldl :: (b -> a -> b) -> b -> [a] -> b foldl f e [] = e foldl f e (x : xs) = foldl f (f e x) xs 1. I understand how these definitions work, and yet I'm unable to implement foldl in terms of foldr. What's a systematic approach to identifying such an implementation, and what is the implementation? 2. I believe that the reverse implementation--namely, implementing foldr in terms of foldl--is impossible. What's the proof of that? 3. Any advice on how, aside from tons of practice, to develop the intuition for rapidly seeing solutions to questions like these would be much appreciated. The difficulty a newbie faces in answering seemingly simple questions like these is quite discouraging. _________________________________________________________________ Express your personality in color! Preview and select themes for Hotmail®. http://www.windowslive-hotmail.com/LearnMore/personalize.aspx?ocid=TXT_MSGT…

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Alternative to Data.Binary
by Grzegorz Chrupala 15 Mar '09

15 Mar '09

Hi all, Is there a serialization library other than the Data.Binary from hackage? I am using Data.Binary in a couple of projects, but I have found its stack and memory usage very hard to control. Its very common that decoding a map or list of non-trivial size uses up all available RAM, or causes a stack overflow. I don't care that much about it being extremely fast, I just want to stop worrying that if I try to read a file a few percent larger than the last time, my program will suddenly stop working. Best, -- Grzegorz -- View this message in context: http://www.nabble.com/Alternative-to-Data.Binary-tp22512229p22512229.html Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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