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This installment of our little series of tutorials will be all about Xtend, a programming language that looks very similar to Java, but which adds some very convenient features. Xtend code compiles to Java and and was developed using Xtext. In fact, once you gain experience working with Xtend you will probably appreciate the power of Xtext even more.


Table of Contents

Preliminaries

There's a few things to do before we dive into the tutorial itself. 

Required Software

For this tutorial, we need you to have Eclipse installed:

  1. Install Eclipse. For what we do, we recommend installing the Eclipse Modeling Tools, with a few extras. Our Wiki page on getting Eclipse has the details: simply follow the instructions for downloading and installing Eclipse and you should be set.
  2. Install the complete Xtext SDK 2.7.3 from the itemis updatesite: http://download.itemis.de/updates/ if you haven't done this already.

Recommended Tutorials

We recommend that you have completed the following tutorials before diving into this one.

  1. Eclipse Plug-ins and Extension Points
  2. Eclipse Modeling Framework (EMF)
    1. This tutorial needs the turingmachine.ecore and the controller you've implemented in the EMF tutorial. If you did not complete the EMF tutorial, you may download a working turing machine here... (in the future).

Required Tutorials

This tutorial continues from the Xtext II 2 - Creating a Grammar from Scratch tutorial thematically. You might want to complete the Xtext I tutorial first.

Extended Brainfuck

Let's play a bit more with Brainfuck (BF). BF is nice, but not nice enough! Let's extend it by adding some syntactic sugar to the language. Feel free to express yourself here but you should at least add the following commands to eBF:

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  1. Open your BF grammar of the previous tutorial (or create a new one) and create rules so that the BF editor accepts the syntax changes.
  2. Re-generate your BF code and run your eclipse instance to verify the changes.

 

Writing a Model Transformation

Now that you extended your BF syntax, it's time to start working on your model transformation. In particular, the first model-to-model (M2M) transformation you're going to write will transform an BF program into another BF program:

  1. Add a new package de.cau.cs.rtprak.<login>.brainfuck.transformations to your BF project.
  2. Add an Xtend Class to the new package.
  3. If you notice that your new class is marked with an error marker because of a missing dependency of the new plug-in project to org.eclipse.xtext.xbase.lib, you can hover over the error with your mouse and have Eclipse add all libraries required by Xtend to your project.

  4. Define an entry method for the transformation that takes a BF program instance as an argument and returns a BF Program. You can use the following (incomplete) method as a starting point:

    Code Block
    languagejava
     /**
 * Transforms a given Turing Machine into an imperative program model.
 *
 * @param machine the Turing Machine to transform into an imperative
 *                program.
 * @return a program model that implements the Turing Machine.
 */
def Brainfuck transformExtendedBrainfuck(Brainfuck brainfuck) {
    // Create the program we will transform the Turing Machine into
    val newBFProgram = BrainfuckFactory::eINSTANCE.createBrainfuck()
  
    // TODO: Your transformation code
  
    // Return the transformed program
    newBFProgram
}

    There's a few points to note here:


    • Lines in Xtend code don't have to and with a semicolon.
    • We have been explicit about the method's return type, but we could have easily omitted it, letting Xtend infer the return type.
    • The keyword val declares a constant, while var declares a variable. Try to make do with constants where possible.
    • The methods you call should be declared as def private since they are implementation details and shouldn't be called by other classes.
    • You may be tempted to add a few global variables that hold things like a global input variable or a pointer to the current state. While you could to that, def create methods might offer a better alternative...

     

  5. Replace the TODO with an transformation code that takes an extended BF program and transforms it into an semantically equivalent BF program that only uses standard BF instructions. 
    HINT: Some of the extended BF commands can only be expressed by standard operations if you can write to other cells. Therefore you are allowed to perform side effects on the tape.
  6. Open the Plug-In Manifest Editor and switch to the Runtime tab. Add the package containing your transformation to the list of exported packages. (You may have to check the Show non-Java packages option in the Exported Packages dialog to see the package.)

Testing your Model Transformation

You will need a way to test the transformation, so we will have to make it available through the UI. Eclipse plug-ins often come with a separate UI plug-in that contains the UI contributions, with the base plug-in only offering the functionality itself. In our case, a brainfuck.ui should already be present. 

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