June 2011 - Beginners

Re: [Haskell-beginners] [web-devel] yesod dependency hell
by Michael Litchard 24 Jul '11

24 Jul '11

My thinking is that this problem comes up anytime someone wants to play around with experimental code. As evidenced by the yesodwiki.cabal file, I think there's a more straightforward solution. I'm just not seeing it. On Wed, Jun 22, 2011 at 1:46 PM, Thomas Hartman <thomashartman1(a)googlemail.com> wrote: > one idea: move .ghc and .cabal to temp directory. > > start over with a clean slate. > > On Wed, Jun 22, 2011 at 1:30 PM, Michael Litchard <michael(a)schmong.org> wrote: >> Configuring Aframe-0.0.1... >> Warning: This package indirectly depends on multiple versions of the same >> package. This is highly likely to cause a compile failure. >> package yesod-auth-0.4.0.2 requires yesod-form-0.1.0.1 >> package yesod-0.8.2.1 requires yesod-form-0.1.0.1 >> package Aframe-0.0.1 requires yesod-form-0.2.0 >> >> I specified in Aframe.cabal yesod-form 0.2.0. The above warning is >> what I was looking to avoid. What is the solution to this problem? I >> could not find an obvious solution in yesodwiki.cabal, even though I >> see it's doing something similar to what I want. How did you deal with >> the above warning message? >> >> On Wed, Jun 22, 2011 at 12:32 PM, Michael Snoyman <michael(a)snoyman.com> wrote: >>> Have a look at the yesodwiki[1]; basically, you can't use the yesod >>> package itself, only the subpackages. This is by design so that a >>> single Yesod release will keep API stability, while users can still >>> experiment with newer versions of underlying packages. >>> >>> Michael >>> >>> [1] https://github.com/snoyberg/yesodwiki/blob/master/yesodwiki.cabal >>> >>> On Wed, Jun 22, 2011 at 10:29 PM, Michael Litchard <michael(a)schmong.org> wrote: >>>> I need to use yesod-form 0.2.0. The problem is that the yesod package, >>>> and the yesod-auth package expect yesod-form to be 0.1.0* >>>> I tried changing the .cabal files but that breaks in ways that makes >>>> me think the fix is not so simple. How do I go about being able to use >>>> yesod-form 0.2.0 >>>> >>>> _______________________________________________ >>>> web-devel mailing list >>>> web-devel(a)haskell.org >>>> http://www.haskell.org/mailman/listinfo/web-devel >>>> >>> >> >> _______________________________________________ >> web-devel mailing list >> web-devel(a)haskell.org >> http://www.haskell.org/mailman/listinfo/web-devel >> >

3 4

Anyone have problems with cabal and SDL?
by Tom Murphy 17 Jul '11

17 Jul '11

When I use Cabal to get any program which depends on the SDL library, this is the error I get. " checking for sdl-config... no checking for sdl11-config... no configure: error: *** SDL not found! Get SDL from www.libsdl.org. If you already installed it, check it's in the path. If problem remains, please send a mail to the address that appears in ./configure --version indicating your platform, the version of configure script and the problem. cabal: Error: some packages failed to install: Raincat-1.1.1.2 depends on SDL-0.6.2 which failed to install. SDL-0.6.2 failed during the configure step. The exception was: exit: ExitFailure 1 SDL-image-0.6.1 depends on SDL-0.6.2 which failed to install. SDL-mixer-0.6.1 depends on SDL-0.6.2 which failed to install. " I have SDL 1.2.14 (correctly) installed on my system. I'd really appreciate any help with this. Tom

4 6

OpenGL keyboardMouseCallback ...confused over type
by Sean Charles 02 Jul '11

02 Jul '11

I asked a question the other day about passing application state around an OpenGL program and I've consulted RWH and the inter-web extensively and I think I am on the right lines so far! In my main program, I use Data.IORef like this: gameState <- newIORef $ newGameState and GameState contains all the stuff to do with the game model. Next the confusing bit... to make myself learn things I typed out the full type of the keyboardMouseCallback function: myKeyMouse :: Key -> KeyState -> Modifiers -> Position -> IO () and slotted it into the code like so: keyboardMouseCallback $= Just myKeyMouse In order to be able to pass the "IORef GameState" into the keyboard handler I have to re-type my keyboardMouseCallback function like so: myKeyMouse :: IORef GameState -> Key -> KeyState -> Modifiers -> Position -> IO () and modify the assignment in main to this: keyboardMouseCallback $= Just (myKeyMouse gameState) But I haven't really understood *why* that is the case. The displayCallback is also similarly affected as it is now: myDisplay :: IORef GameState -> IO () ... displayCallback $= (myDisplay gameState) and again I am not sure what magic is happening here to have made it compile and work! My real source of confusion is over my apparent victory over the type system in that I appear to have extended the type signature (is that the correct term?) for both of the callbacks be prepending "IORef GameState" to them and yet it all compiles and works. Is "prepending" the key ? I feel a tingling of Eureka! organ but I am not sure yet. Explanations are welcome as I am sure there is something "important" here that will really advance my understanding of the type system. It smells like curry but I don't think... hang on... the keyboard one is wrapped in the Maybe monad... therefore(?) the function I am handing in can be *any* type so long as they actually match types! Is that it then? I can smell partial application and curry now. HELP! Thanks, Sean.

4 7

version of base in Haskell Platform
by Dennis Raddle 01 Jul '11

01 Jul '11

I just installed the latest Haskell Platform on Windows XP. Then I tried to install the musicxml package, and it says it needs base 3.something. How do I find out what version of base comes with a version of the Haskell Platform? Thanks, Dennis

3 2

GOTCHA! OpenGL window behaviour is mis-spelled...
by Sean Charles 30 Jun '11

30 Jun '11

This caught me out for several frustrating minutes until I finally saw the problem... package: Graphics.UI.GLUT.Begin data ActionOnWindowClose has three constructors, and I wanted the third one which I glanced at and then spelled it how I knew it *should* be: ContinueExecution which gave me an error, and finally I realised that as an English word it is in fact spelled incorrectly in the code, like so: ContinueExectuoin HTML Link: http://hackage.haskell.org/packages/archive/GLUT/latest/doc/html/Graphics-U… Is this one of those "accepted things" as in, too difficult to change because it will break stuff or could it be changed ? All the best, Sean.

2 1

Global variables
by ARJANEN Loïc Jean-David 30 Jun '11

30 Jun '11

Hello, For a pet project I need a global counter, giving how many times a given function was called. What would you use for that purpose ? Loic

8 11

A first try
by Panagiotis Koutsourakis 30 Jun '11

30 Jun '11

Hello all, I've been spending some time recently learning Haskell. I am not a newbie in programming, and I've had some experience with lisp in the past, but I have not really studied functional programming. I am mostly seeking feedback regarding style, and glaring mistakes that I may make in some toy examples, but I am not sure if this is the proper place to ask. In case it is though, here is an attempt (not yet complete) at the word count program: http://pastebin.com/JZw22QGA Thanks in advance! -- Panagiotis Koutsourakis

11 48

Re: [Haskell-beginners] Understanding category theory
by Arlen Cuss 29 Jun '11

29 Jun '11

On 30/06/2011 10:26 AM, Christopher Howard wrote: > Would anyone recommend a particular book or tutorial to help me > understand category theory? I've tried reading a few tutorials i've > googled, but even the "beginner" ones are very difficult and seem to > assume a lot. I've just started reading this, found on /r/haskell on Reddit: http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.78.7317&rep=rep1&t… It's quite readable, may require a little effort though!

1 0

Re: [Haskell-beginners] Understanding category theory
by Jake Penton 29 Jun '11

29 Jun '11

On 2011-06-29, at 8:26 PM, Christopher Howard wrote: > Would anyone recommend a particular book or tutorial to help me understand category theory? I've tried reading a few tutorials i've googled, but even the "beginner" ones are very difficult and seem to assume a lot. > I just picked up the book by Benjamin Pierce entitled Basic Category Theory for Computer Scientists. It is pretty good; at least I am making some headway in it. I have another more recent book by Pierce called Types and Programming Languages, which I found to be very readable, so I am a bit of a fan of Pierce. It is not an easy topic, IMHO. I have a B.Sc. in math, and am currently doing a master's degree in software engineering. I find functional programming literature that purports to be tutorial in nature (as opposed to research oriented) some of the most impenetrable stuff I have ever read. Reading it is like trying to eat a bowl of steam with a fork. Good luck.

1 0

Understanding category theory
by Christopher Howard 29 Jun '11

29 Jun '11

Would anyone recommend a particular book or tutorial to help me understand category theory? I've tried reading a few tutorials i've googled, but even the "beginner" ones are very difficult and seem to assume a lot. Sent from my HTC

1 0