- Beginners - Haskell.org

Haskell and TimeZones
by Thiago Negri 03 Jan '12

03 Jan '12

Hi, How does Haskell handle TimeZone? Do I need to use Oslon to have a historical database of TimeZones in Haskell? I tried reading the package description and everything, but it seems complicated. Is there any easy to follow tutorial available? For example, here in Brazil the daylight savings rules change every year. How do I update the Haskell Data.Time.* packages to know of the new rules? Or does it uses the TimeZone database from O.S.? I'm looking for a solution that works in any platform (mac, linux, windows). Thanks, Thiago.

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Fundamentals of List Comprehension and Recursion
by Cody Haberkorn 03 Jan '12

03 Jan '12

Hi all, I high school programmer and just started learning Haskell. Haskell so far seems to be an awesome language. I began reading "Learn you Haskell for a Great Good!" I am confused with list comprehension, as I am coming from an imperative programming language (Java). From my understanding, list comprehension is synonymous to Java's for-loop and what not. For example: let xs = [1,2,3,4,5] [x | x <- xs] I believe it is saying that "bound x to xs, and do (print) x." Another example: let rightTriangles' = [ (a,b,c) | c <- [1..10] , b <- [1.. c], a <- [1.. b], a^2 + b^2 == c^2, a+b+c == 24] ghci > rightTriangles' [(6 ,8 ,10)] I believe it is saying "store c with the numbers 1-10, b is length of c, and a is the length of b. Print the answer (a,b,c) which satisfies a^2 + b^2 == c^2, a+b+c == 24. It may seem that I am answering my own question, but when it becomes more complicated or I am ask to do specific tasks that involves list comprehensions, I do not know how to read or compose one. Second, can someone do a line by line breakdown of this code? The book does a sub-par job explaining it. -- Creating our own sum function sum ' :: (Num a) => [a] -> a sum ' [] = 0 sum ' (x:xs) = x + sum ' xs Summed up: How did you learn Haskell and how long did it take before you became competent? This is my second day and I am already running into problems. I have to re-read things where as Java it came easy to me. Any book or tutorials? Can someone explain list comprehension and my recursion code? Thanks, - Cody p.s The questions so far have been over my head (is this a " true beginner's email list"?), I'll try to answer what I can.

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ghc-pkg
by Gregory Guthrie 03 Jan '12

03 Jan '12

What is the remedy (is there a simple remedy?) if "ghc-pkg check" reports something amiss? ------------------------------------------- C:\Users>ghc-pkg check There are problems in package hoogle-4.2.6: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package warp-0.4.3: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package wai-0.4.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package http-types-0.6.5.1: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package case-insensitive-0.3.0.1: dependency "hashable-1.1.2.1-25dfe4e720b096d06d0cf57f76c49caf" doesn't exist There are problems in package blaze-builder-enumerator-0.2.0.2: dependency "blaze-builder-0.3.0.1-157e8a92bc5ef27895f938613ecfdcb1" doesn't exist There are problems in package scion-0.1.0.9: dependency "AttoJson-0.5.10-4932e72997280d8c2e35b4aca3328284" doesn't exist The following packages are broken, either because they have a problem listed above, or because they depend on a broken package. hoogle-4.2.6 warp-0.4.3 wai-0.4.1 http-types-0.6.5.1 case-insensitive-0.3.0.1 blaze-builder-enumerator-0.2.0.2 scion-0.1.0.9

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Re: [Haskell-beginners] suggestions for optimizing sudoku solver
by Ray Song 03 Jan '12

03 Jan '12

An array with destructive updates (IO/ST) may help. You can also look into the exact cover problem and dancing links. If I recall correctly, this problem can be transformed to a 729*324 matrix. 在 2012-1-3 上午8:10，"Peter Hall" <peter.hall(a)memorphic.com>写道：

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Audio packages
by Sourabh 03 Jan '12

03 Jan '12

Thanks for the reply. I will give wxHaskell a shot for the audio. Any ideas on how to resolve #2? > Finally, I have started getting this error every time I do a cabal install now: > Setup.hs:1:8: > Could not find module `Distribution.Simple': > Use -v to see a list of the files searched for. > 2. What should I do to get cabal to start installing stuff again?

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Re: [Haskell-beginners] suggestions for optimizing sudoku solver
by Peter Hall 03 Jan '12

03 Jan '12

Thanks, It was really just an exercise that I'd set myself, and I wouldn't buy a book just for that. But, you're second person to recommend it to me, and it should have some good insight that will help me think the right way about other problems, so I've ordered it. Any other more general comments about my code? Peter On Mon, Jan 2, 2012 at 11:01 PM, Michael Serra <mk.serra(a)gmail.com> wrote: > This book by Richard Bird covers optimizing a Sudoku solver with equational > reasoning, along with quite a few other algorithms. > > On Sun, Jan 1, 2012 at 9:27 PM, Peter Hall <peter.hall(a)memorphic.com> wrote: >> >> I set myself a learning task of writing a sudoku solver. >> (https://github.com/peterjoel/sudoku/blob/master/src/Sudoku.hs) >> It works pretty well, but struggles with some of the harder grids. >> e.g. data/hard4.txt and data/hard5.txt take around 18 seconds to >> solve. Obviously there's a limit, but I feel like I should be able to >> make this faster. >> >> I think the main issue is reading/writing to the cells in the grid, >> since (!!) is O(n). Even though it never has to go beyond index 8, it >> will add up over the millions of times it has to do it. I imagine it >> could be a lot faster if I use a static, non-list data structure, but >> I was hoping to keep it a bit more flexible. >> >> Also, I'm struggling to get started with performance profiling. Can >> someone point me to some good resources? >> >> Peter >> >> _______________________________________________ >> Beginners mailing list >> Beginners(a)haskell.org >> http://www.haskell.org/mailman/listinfo/beginners > >

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Testing the water
by Cody Haberkorn 01 Jan '12

01 Jan '12

A little unsure of how this works, but we'll see! Thanks, - c

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..
by Alia 01 Jan '12

01 Jan '12

Hi, ok, no problem! http://ekolifelaguna.99k.org/pilspharmnew1029361.php?lyxipageID=57 Sun, 1 Jan 2012 6:22:15 _____________________ "With proper tools and much ingenuity some of these appliances may be home-made.The making of the tuner, the wiring, the aлrial and the assembling are all technicalities that may be mastered by a careful study of the subject and the result will be a simple and inexpensive set having a limited range." (c) Joshuaneph wreless

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Audio packages.
by Sourabh 31 Dec '11

31 Dec '11

Hello, I'm a Haskell beginner and am working on my first *serious* haskell project. After going through a few books, and working on the exercises in the books, I finally started writing a small 2D game in Haskell. I figured this would give me lots of exposure to Haskell, and also on how graphics, keyboard, sound, etc are done. Also, I'm working on windows, so unfortunately building the correct libraries has been a bit of a pain. In fact, my question pertains to this. I am currently at the stage where I can get various events to happen correctly in the game, but there is no sound. I started looking at various audio related packages earlier today, but I can't seem to find any documentation on any packages. To add to my woes, I just can't, for the life of me, get any packages to install correctly on windows. So far I have tried OpenAL, SDL-mixer, PortAudio on windows, and none of them seem to work. Cabal install outright fails and asks me to go the MinGW/msys route. When I try to go through this route (which worked successfully for me for graphics), I still can't get any libraries to build. The various errors I have encountered range from configure/build failing, to dependencies not installing correctly. Looking at the various hits on google, it seems that I am not alone in this. I finally managed to get SDL to install (but not SDL-mixer). Even though SDL has an Audio component to it, the lack of documentation on the API has left me with no way to figure out how to actually use this...? Link that worked for me: http://www.animal-machine.com/blog/2010/04/a-haskell-adventure-in-windows/ Finally, I have started getting this error every time I do a cabal install now: Setup.hs:1:8: Could not find module `Distribution.Simple': Use -v to see a list of the files searched for. Have I finally done something terrific and blown everything apart? Sadly, instead of spending time writing Haskell code, I find myself spending a lot of time getting libraries to install and work on Windows. Is this common, or am I doing something wrong? At this point I would very much like advice on a couple of things: 1. Does anyone know any good Audio packages, that would work on windows, along with some examples and documentation of the API? 2. What should I do to get cabal to start installing stuff again? I apologize if I sound a bit frustrated, because I guess I am. :) Thanks for any advice, and have a happy new year!

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basic data types
by Stanisław Findeisen 31 Dec '11

31 Dec '11

Hi What are those basic data type instances? For example here: http://www.haskell.org/ghc/docs/latest/html/libraries/base/Prelude.html#t:B… we have: Instances Bounded Bool Enum Bool Eq Bool Data Bool Ord Bool Read Bool Show Bool Ix Bool Typeable Bool Generic Bool Storable Bool What is the difference between, e.g., Bounded Bool and Enum Bool? -- This e-mail address is invalid, see: http://people.eisenbits.com/~stf/public-email-note.html . OpenPGP: E3D9 C030 88F5 D254 434C 6683 17DD 22A0 8A3B 5CC0

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