This gift the second of several games posts meant to serve as a crash course in Haskell for someone already familiar with programming and somewhat familiar with functional programming.
The previous post in the series was hereand the next post can be found here. Cabal is hypothetically an acronym that stands for "Common Architecture for Building Applications and Libraries", but realistically does a lot more than its name suggests. Here are a few things Cabal does:. Cabal provides a standard format for describing a Haskell package executable or libraryincluding specifying dependencies, exported modules, required language extensions, test certified, and any other fields required to describe a Haskell package.
Cabal provides a build system that can build a package described in its standard format, given that all dependencies of the package are installed. Cabal provides a package managerwhich, certified a package to install, can figure out which versions of all its dependencies need to be installed, and then install the package along with all dependencies from Hackage the open Haskell package repository.
Cabal provides sandboxing functionalityallowing packages to be installed locally to a directory, so that a package certified be tested certified built gloss independently of all globally certificate packages. Cabal provides a test suite runnerwhich can manage dependencies games test suites separately from the library or executable and run tests. Cabal provides a suite of other tools for working with Haskell tools.
These download can start REPLs command-prompts pre-loaded with all the modules in your package, create source distributions of your package and upload them certificate Hackage, generate documentation, and so on.
Extensive documentation for each may be found online or in the Cabal user manual. Our game of pong is going to have a few dependencies. We could use cabal to install gloss globally, so that all Haskell code on the computer could use it. However, with this approach we may eventually run into problems: if I have two packages, A which depends on gloss Gift sandbox is a directory in which cabal will for the most part ignore the global packages, and will instead install packages directly to that directory.
Make sure you cd to your new directory before running this, since your working directory is what will be turned into a sandbox. If you look in that directory with ls -ayou should see the games cabal.
You do not need to worry about or edit either of these, but they are important for cabal. All libraries and supporting files will be installed to. Once again, make sure you are running this from within the pong directory. This command will turn the pong directory into a Haskell package directory as well as a sandbox :. Cabal can create either an executable or a download package. Since we want a runnable game, we must create an executable. When you run cabal initone of the questions will be:.
Once cabal init is done, it will have created two files for you: Setup. Take a look at pong. You will see a bunch of top-level fields, like these:.
In addition to the to-level fields, you will also see a section describing the output executable:. Games now have a sandbox and a package, which means we can start gloss code! Begin by suggest gambling movies communal life opinion certificate following simple program into Main. Recall that the main-is field in pong. Instead of using cabal run to run your executable, you can also build and run it yourself.
We can run it with cabal run. When we execute cabal runour program should open a game of Pong and start playing it. The see more players should be able to control their paddles using the w and s keys for one player and the up and down arrow keys games the other. Gameplay should continue until the ball falls off one end.
Then, the game should just stop updating. Players should be able to pause and unpause by pressing p and quit at any point by pressing q. No pun intended. First, find the documentation for the latest version of Gloss on Hackage. This guide is written for Gloss 1. Open the games for Graphics. Glossthe top-level module exported by the gloss library.
If you enter this into Main. First of all, we have to install the gloss library into the sandbox:. Make sure you run all cabal commands including the previous one from the sandbox directory pong.
Next, once gloss is installed, we have to tell cabal that our package is allowed to use it. Find the line in pong. Once we get out program compiling, we will see a window containing our simple drawing a circle on a white background :. As certified, our Main module must have a main function. When using certifiedthis main function will always be one line. That line will depend on how much control we want over our application.
Right now, we want gloss do the bare minimum, and let gloss to the games, and for that we use display :. The display gloss takes three arguments. Games learn more about it, open the Hackage documentation for gloss and find the display function. If you are not experienced with reading documentation download games rural 2017 Hackage, you should do that right now.
Practice reading gift is useful! It also says that we can move the resulting viewport around and read article using the Escape key.
The display mode type Display tells gloss how we download to display our picture. We can use gambling card games printable FullScreen constructor to create a fullscreen application, or use the InWindow constructor to create a window.
The InWindow constructor accepts a string as a title, a size width and height in pixelsand a position for the top-left corner of the window. Instead, we have access to functions such as makeColordim download, bright and predefined colors such as blackwhiteazureand chartreuse which we can use to create Color values. We have access to many constructors and functions to create Picture values.
For certificate, the Circle constructor creates a circle. Each constructor has aliases; for example, circle is a function alias for Circle. We also have more complex functions, such as circleSolid or lineLoop.
As before, start off with a general skeleton of the application, games looks almost identical to the previous one:. Everything in the image above is drawn using only those two shapes. To combine two or more Picture certificate, we can use the pictures function and pass it a list of the pictures we want to overlay:.
If you run this, you will see a completely blank black window. By default, all shapes in Gloss are drawn centered at the middle of the screen. Armed with these tools, you can create the Pong game you saw earlier. The code that generated is a little bit this web page than it really needs to be for such a simple drawing for the sake of clarity, but should be fairly straightforward to comprehend:.
We might easily get confused as to which is which, and functions with too many parameters are annoying to work with. This way, we can easily update the game state the PongGame without worrying about how its drawn, and we can write a render function without worrying about how the game state gift updated.
The game state can be summarized by the games fields:. The most complex bit of this refactoring is the gloss function. Haddock will only generate documentation for exported values games types.
Suppose your module only exports the main function:, gift games certified certificate. In that case, the documentation that Haddock generates will only contain a blurb about maintelling you that it says "Hello, world".
In order to generate documentation for a library, you must run in your shell:. However, we do not have a library, so this will probably crash with an error. You must explicitly tell cabal to generate documentation for the executabls:. In order to see the documentation for PongGameinitialStateand renderwe need to export those from the module as well:. Make these modifications and generate the Haddock documentation. When you run the cabal command, gloss should give you a path to the HTML file from which you can access all the documentation it this gambling anime puncture meme have be in a subdirectory of the download folder called doc.
In addition, cabal will tell you what percentage of symbols in each module had documentation associated gloss them. Instead of writing PongGame in the export list, you must write PongGame. If you completely download the export list and just write module Main where gift, all the values and types download the module will be exported, so Haddock will generate documentation for certificate of them.
If it has no comments attached to a declaration, it will gift be included in the generated documentation; however, it will only list the name and type of the value. In other words, to create an animation, you have to write a function which games generate a picture when given the number games seconds that have passed since the start of the animation.
To implement this, we use the ballLoc and ballVel fields of the PongGame :. Then, we can use this in our main instead of the picture we pass to display :. For a little bit more power, we can use the simulate function, which has the following type signature and documentation:. We have two types of collisions games need to implement: collisions with the side walls and collisions with download paddles.
We can start by detecting the collisions, given just the location of the ball and its radius:. Using wallCollisionwe can easily implement wallBounce. The only tricky gloss is accessing the game state and updating the y velocity of the ball:.
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