Friday, 31 July 2015

Haskell - playing with Hackage

OK, so you have just finished reading your first Haskell book, you understand most of (if not all!) compilation errors GHC throws at you and you start thinking creatively about the language. If you are at this stage and wondering what's next, welcome to my team! Not so long ago I finished Learn you a Haskell and, while reading The Haskell Road to Logic, Maths and Programming, I decided I was ready to start playing with Hackage. My package of choice was Rasterific - mostly because I wanted to get something on the screen quickly.

In this update I'm going to walk you through installing a package of your choice (+ all its dependencies) in your local cabal sandbox and using it in your own Haskell program. Let's get started!

First of all, let's make sure you have the latest versions of

  • Cabal
  • cabal-install
installed. To do that, simply run the following command from your command line:
cabal install Cabal cabal-install
This will install the latest versions of both packages.

Once it's done, let's update cabal packages using the following command:

cabal update

Now, a special note for the Haskell Platform users: the cabal you are using from the command line might not (and it wasn't in my case) be the one being updated! In my case, the cabal my PATH variable was pointing at was located in the Haskell Platform folder

...\Haskell Platform\2013.2.0.0\lib\Cabal-1.16.0
but executing those commands made the cabal install its latest version in
C:\Users\Piotr\AppData\Roaming\cabal\bin (version
I had to come up with a solution and I ended up changing my PATH variable to use the cabal installed in my AppData.

Once you have the PATH variable pointing at the updated cabal, navigate to the folder you want to place your experimental project in (still using the command line) and type:

cabal sandbox init
This will create a folder-local sandbox environment for packages that could have otherwise damaged your global cabal repository. In case anything goes wrong in the sandbox, you can always delete it and start fresh - no need to modify your global set of packages.

Once you have the local sandbox prepared, you are ready to install your package of choice and its dependencies. Just in case, make the first run dry (just list the required dependencies):

cabal install Rasterific --dry-run
You should see something like this:
Resolving dependencies...
In order, the following would be installed:
base-orphans-0.4.0 (new package)
bytestring- (new version)
Win32- (new version)
binary- (new version)
text- -integer-simple (new version)
hashable- (new version)
nats-1 (reinstall) changes: hashable- ->
time- (new version)
directory- (new version)
FontyFruity- (new package)
mwc-random- (new package)
unordered-containers- (new version)
semigroups- (reinstall) changes: bytestring- ->,
hashable- ->, text- ->,
unordered-containers- ->
bifunctors-5 (new version)
vector-algorithms-0.7 (new package)
void-0.7 (reinstall) changes: hashable- ->
contravariant- (new version)
comonad- (new version)
profunctors-5.1.1 (new version)
semigroupoids- (new version)
free-4.12.1 (new version)
zlib- (new version)
JuicyPixels- (new version)
Rasterific-0.6.1 (new package)
Warning: The following packages are likely to be broken by the reinstalls:
Use --force-reinstalls if you want to install anyway.

Once you're happy with required dependencies, simply run:

cabal install Rasterific

If everything goes well, you are ready to start playing with the package! You can find Rasterific documentation here. I used it to write a small program drawing rectangles into a file:

import Codec.Picture(PixelRGBA8( .. ), writePng)
import Graphics.Rasterific
import Graphics.Rasterific.Texture

main :: IO ()
main = do
    let backgroundColour = PixelRGBA8 234 247 217 255 -- Cilantro Creme
        foregroundColour1 = PixelRGBA8 195 214 170 255 -- Mint Sherbert
        foregroundColour2 = PixelRGBA8 142 168 108 255 -- Pesto Paste
        foregroundColour3 = PixelRGBA8 77 100 45 255 -- Simple Green
        foregroundColour4 = PixelRGBA8 40 58 16 255 -- Dark Water
        image = renderDrawing 400 400 backgroundColour $ do
            withTexture (uniformTexture foregroundColour1) . fill $ rectangle (V2 50 50) 145 145
            withTexture (uniformTexture foregroundColour2) . fill $ rectangle (V2 205 50) 145 145
            withTexture (uniformTexture foregroundColour3) . fill $ rectangle (V2 50 205) 145 145
            withTexture (uniformTexture foregroundColour4) . fill $ rectangle (V2 205 205) 145 145
    writePng "test.png" image

-- palette taken from:
You can also find the code here. To build it, execute the following command (and this is where a local sandbox comes very handy):
ghc -package-db=.cabal-sandbox\i386-windows-ghc-7.6.3-packages.conf.d main.hs
Once the program compiles, you can run it and start drawing. Here is my result:

And that's it! You have just installed your first package and used it in your own program. Please leave a comment if the installation process was different for you or if you experienced some other problems.

Let the adventure with Hackage begin!

No comments:

Post a Comment