I am refactoring an Xtext project developed on an older version and notice that, by default, the Xtext framework now generates Java classes in place of what used to be Xtend classes.
Is the Xtext project moving towards Java recently? Is this to harness Java's updates? What does it mean for Xtend within Xtext?
I am curious because my project uses a lot of extension methods and string templates, so I need to know if I should update my code at some point.
https://blogs.itemis.com/en/xtext-2.20-release
To be more specific, we still think that Xtend is the most powerful language supporting template expressions. The most common use case for this are code generators. Besides that, writing unit tests with Xtend feels much cleaner than with Java.
However, we decided to encourage to use Xtend only for these areas, and not as the primary general-purpose language. And we start doing this with the “New Project” wizard. The configuration that this wizard creates for a new Xtext project, will now use Java as the language for generated skeleton classes, so that newly-created projects (and especially new users) are using Java by default.
The Xtext project started to discourage the usage of Xtend where the latter’s language features do not have a significant benefit over Java. And internally, the project started to refactor the codebase to follow this recommendation.
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I used MPS in the past in a small project (like a lab-project), so I have basic understandings of how to use MPS (though it was version 2.4 or something alike). Now I'm trying to introduce some utility software (ideally, plugin for IntelliJ) built on top of MPS functionality. As MPS is not that widely used, I'd like to consult with experienced people here.
What I want to do is to wrap some relational knowledge database access (SQL queries) into MPS-based plugin. I want to be able to start quickly and generate code to already existing jdbc-wrapping library, and in future I want to be able to switch to my implementation with added db-specific features. In the same time I want to preserve existing user models so that they could switch to a new language easily, and fall back if something is wrong with this new language. How this easy-switch feature could be achieved? My first idea was using abstract language without generators, and adding implementation language in mps-based module in Idea as a dependency (one or another), but I'm not sure if this is easily possible.
Yeah, if I understand you correctly, this should be easily possible. You don't need to make a language without generators, but can design your language with generators and all. Then, if you want to simply add new constructs that users will be able to use in addition to already defined constructs, you can extend this language with a more specific language for db-specific features (in case you want to have more than one specializing language).
Alternatively, if you want to keep using the same language and update it, MPS offers migration scripts in which you can specify how to upgrade existing models that were built in an older version of your language to a newer version.
For a starting point on making an Idea plugin with MPS, please see https://confluence.jetbrains.com/display/MPSD30/Using+MPS+inside+IntelliJ+IDEA.
Is it a must to know Groovy to start learning Ofbiz? The one book i can find is for version 4 of ofbiz and it uses Beanshell. I don't know if later versions of ofbiz have added support for groovy.
Objective: to create workflows as necessary.
Thanks.
EDIT: Found this. From what i understand, one can use any compliant Java scripting language.However, Groovy will be supported OOTB. (Groovy is not just a scripting language, but it is one of the roles)
Later versions have added support for Groovy.
AFAIK, you can still use Beanshell if you want
No, you shouldn't, unless you want use not java but groovy to develop something - e.g, event, service - for OFBiz.
If you familiar with java, that's enough for you to read and understand the source code written in groovy, and it's enough in most case to write some simple in-line groovy script used in OFBiz.
"Know groovy", it's nice-to-have but not must to "start learning OFBiz".
Groovy is used a lot in screen actions, which is the data preparation code that is part of generating UI output. There is a lot of code in the project like this.
It can also be used to implement services and request events (used for processing input), and is a popular tool for custom extensions to OFBiz even though not used a lot in OFBiz itself.
As stated in other answers if you know Java it's easy to read most Groovy code (some closure syntax can be confusing at first), but it's worth learning about more to reduce code size and effort, and make your code cleaner and easier to maintain. In other words, Groovy has a lot of extensions beyond plain Java that are very useful, especially for business logic in applications like those built with Apache OFBiz.
As a case in point, the next generation framework based on the ideas in OFBiz (Moqui Framework, www.moqui.org) is written largely in Groovy and supports Groovy for everything whereas OFBiz also uses JUEL for expressions (and even Beanshell still in a couple places). I should note that both frameworks support a number of other scripting languages for business logic if you have other strong preferences, but it is nice to standardize on one so that developers have less to learn and can more easily work with existing business logic and (as applicable) framework code.
I'm currently writing an embedded application for J2ME environment (CLDC 1.1 configuration and IMP-NG profile). Being spoiled by all those new features in JVM-based languages (Groovy, Scala, Clojure, you name it), I was considering using one of them for my code.
However, most of the mentioned languages require pretty decent JVM environment. Most so-called "dynamic" languages require the VM to have reflection. Many ask for annotations support. None of the above features are available under J2ME.
From what I found, Xtend looks like a viable options, as its compiler spits out plain Java, not bytecode, and doesn't require any library for runtime needs. Of course, the generated Java code also must meet some requirements, but Xtend webpage looks promising in this regard:
Xtend just does classes and nothing else
Interface definitions in Java are already nice and concise. They have a decent default visibility and also in other areas there is very little to improve. Given all the knowledge and the great tools being able to handle these files there is no reason to define them in a different way. The same applies for enums and annotation types.
That's why Xtend can do classes only and relies on interfaces, annotations and enums being defined in Java. Xtend is really not meant to replace Java but to modernize it.
Am I right and it is possible to compile Xtend-generated code for J2ME platform, or there are some constructs that will not work there?
Alternatively, can you recommend any other "rich" Java modification language that can be run on J2ME?
Update: Knowing that the "compiler" producing results as another source code is called transcompiler, one can also find Mirah, a tool which requires no runtime library and specific Java features.
Xtend's generated code uses google guava heavily. If that is compatible to the J2ME, Xtend could be the language of your choice. I'm not aware of anything that prevents from using it on other platforms that provide a dedicated development kit (e.g. Android).
In addition to being able to generate Java source, Mirah recently added support for javac's --bootclasspath option, which allows you to generate your bytecode against a non-standard version of the java core classes, e.g. LeJOS.
It's still a little fresh, but it'd be nice to have more people using it on different javas.
We all know that MetaProgramming is a Concept of Code == Data (or programs that write programs).
But are there any applications that use it & what are the advantages of using it?
This Question can be closed but i didnt see any related questions.
IDEs are full with metaprogramming:
code completion
code generation
automated refactoring
Metaprogramming is often used to work around the limitations of Java:
code generation to work around the verbosity (e.g. getter/setter)
code generation to work around the complexity (e.g. generating Swing code from a WYSIWIG editor)
compile time/load time/runtime bytecode rewriting to work around missing features (AOP, Kilim)
generating code based on annotations (Hibernate)
Frameworks are another example:
generating Models, Views, Controllers, Helpers, Testsuites in Ruby on Rails
generating Generators in Ruby on Rails (metacircular metaprogramming FTW!)
In Ruby, you pretty much cannot do anything without metaprogramming. Even simply defining a method is actually running code that generates code.
Even if you just have a simple shell script that sets up your basic project structure, that is metaprogramming.
Since code as data is one of key concepts of Lisp, the best thing would be to see the real applications of projects written in these.
On this link you can see an article about a real world application written partly in Clojure, a dialect of Lisp.
The thing is not to write programs that write programs, just because you can, but to add new functionality to your language when you really need it. Just think if you could simply add new keyword to Java or C#...
If you implement metaprogramming in a language-independent way, you get a program analysis and transformation system. This is precisely a tool that treats (arbitrary) programs as data. These can be used to carry out arbitrary transformations on arbitrary programs.
It also means you aren't limited by the specific metaprogramming features that the compiler guys happened to put into your language. For instance, while C++ has templates, it has no "reflection". But a program transformation system can provide reflection even if the base langauge doesn't have it. In particular, having a program transformation engine means never having to say "I'm sorry, your language doesn't support metaprogramming (well enough) so I can't do much except write code manually".
See our DMS Software Reengineering Toolkit for such a program transformation system. It has been used to build test coverage and profiling tools, code generation tools, tools to reshape the architecture of large scale C++ applications, tools to migrate applications from one langauge to another, ... This is all extremely practical. Most of the tasks done with DMS would completely impractical to do by hand.
Not a real world application, but a talk about metaprogramming in ruby:
http://video.google.com/videoplay?docid=1541014406319673545
Google TechTalks August 3, 2006 Jack Herrington, the author of Code Generation in Action (Manning, July 2003) , will talk about code generation techniques using Ruby. He will cover both do-it-yourself and off-the-shelf solutions in a conversation about where Ruby is as a tool, and where it's going.
A real world example would be Django's model metaclass. It is the class of the class, from which models inherit from and responsible for the outfit of the model instances with all their attributes and methods.
Any ORM in a dynamic language is an instant example of practical metaprogramming. E.g. see how SQLAlchemy or Django's ORM creates classes for tables it discovers in the database, dynamically, in runtime.
ORMs and other tools in Java world that use #annotations to modify class behavior do a bit of metaprogramming, too.
Metaprogramming in C++ allows you to write code that will get transformed at compilation.
There are a few great examples I know about (google for them):
Blitz++, a library to write efficient code for manipulating arrays
Intel Array Building Blocks
CGAL
Boost::spirit, Boost::graph
Many compilers and interpreters are implemented with metaprogramming techniques internally - as a chain of code rewriting passes.
ORMs, project templates, GUI code generation in IDEs had been mentioned already.
Domain Specific Languages are widely used, and the best way to implement them is to use metaprogramming.
Things like Autoconf are obviously cases of metaprogramming.
Actually, it's unlikely one can find an area of software development which won't benefit from one or another form of metaprogramming.
Does anyone have experience working with language workbench tools such as Xtext, Spoofax, and JetBrains' MPS? I'm looking to try one out and am having a hard time finding a good comparison of the different tools. What are the pros and cons of each?
I'm looking to build DSLs that generate python code, so I'm especially interested to hear from people who've used one of these tools with python (all three seem pretty Java-focused... why is that?). The DLSs are primarily for my own use, so I care less about building a really pretty IDE than I do about it being KISS to define the syntax and write the code generator. The ability to type-check / do static analysis of the DLSs would be pretty cool too.
I'm a little afraid of getting far down a path, hitting a wall, and realizing that all my code is in a format that can't be ported to anything else -- is that a risk with these tools? MPS in particular seems a little scary since as I understand it you don't really generate text-based syntaxes but rather build specialized editors for ASTs.
Markus Voelter does a pretty good job comparing those three in se-radio and Software ArchitekTOUR podcasts.
The basic idea is, that Xtext is most used, therefore most stable and documented, and it is based on popular Eclipse platform and modeling ecosystem - EMF which surrounds it. On the other hand it is parser based and uses ANTLR internally, which means the kind of grammars you can define is limited and languages cannot be combined easily.
Spoofax is an academic product with least adoption of those three. It is also parser based, but uses its own parser generator internally which allows language combinations.
Jetbrains MPS is projection based, which gives much freedom to language designer and allows combinations of languages. *t also has solid support. Drawback might be the learning curve.
None of these tools is strictly Java focused as target language for code generators. Xtext uses Xpand templates, which are plain text. I don't really know how code generation in Spoofax works. MPS has its base language, which is said to be subset of Java, but there are different alternatives.
I personally use Xtext because of its simplicity and maturity, but those strong limitations given by its design make it not a very future proof choice.
I have chosen XText in the same case two weeks ago, but I don't know anything about Spoofax.
My first impression - Xtext is very simple and productive.
I have made my first realife(but very simple) project in 30 minutes, I have generated a graphviz dot graph and html report.
I don't like MPS because I prefer plain text source and destination files.
There are other systems for doing this kind of thing. If your goal is building tools, you don't necessarily have to look to an IDE with an integrated tool; sometimes you can find better tools that have focused on utility rather than IDE integration
Consider any of the pure program transformation tools:
TXL (practical, single paradigm)
Stratego (Spoofax before it was transplanted into Eclipse)
Rascal (research, very nicely designed in many ways)
DMS Software Reengineering Toolkit (happens to be mine; commercial; used to do heavy duty DSL/conventional langauge analysis and transformation including on C++)
These all provide good mechanisms for defining DSLs and transforming them.
What really matters is the support machinery for carrying out "life after parsing".
I 've experimented for a couple of days with Xtext and while the tool looks promising I was eventually put off by the tight integration with the Eclipse ecosystem and the pain one has to go through just to solve what should be given hassle-free out of the box: a headless run of the code generator you implemented. See here for some of the minutiae one has to go through (and it's not even properly documented on the Xtext web site but rather on a blog, meaning its an ad-hoc patch that could very well break on the next release).
Will take another look in half a year to see if there has been any improvement on this front.
Take a look at the Markus Völter's book. It does a very comprehensive comparison of these 3 technologies.
http://dslbook.org
XText is very well maintained but this doesn't mean it's problem-less. Getting type-system, scoping and generation running isn't as easy as advertised.
Spoofax is scannerless, (simplifying grammar composition). Not that well documented, but seems complete.
MPS is projectional. A pro for language composition and con for editing. Supports multiple editors for an AST and will soon even support a nice diagram editor. Base language documentation isn't that good. Typesystem, scoping, checking is very well handled. Model to model transformations are done by the solver. My colleagues using it complain about model to text languages. (My opinion M2M wasn't that intuitive either.)
Years ago Microsoft had the OSLO project. MGrammar and especially Quadrant were very promising. It was possible to represent your model in table, form, text or diagram view. But suddenly they've cancelled the project (and perhaps shot the people working on it)
Perhaps today the best place to compare different language workbenches is http://www.languageworkbenches.net/ and there http://www.languageworkbenches.net/past-editions/ shows how a set of Language Workbenches implement a similar kind of task: a dsl for a particular domain.
Update 2022: as links were broken and newer articles on the topic are written see the site referred above at:
https://web.archive.org/web/20160324201529/http://www.languageworkbenches.net/
References to article reviewing language workbenches include: 1) State of the art: https://link.springer.com/chapter/10.1007/978-3-319-02654-1_11 and 2) Empirical evaluation: https://hal.archives-ouvertes.fr/file/index/docid/706841/filename/Evaluation_of_Modeling_Tools_Adaptation.pdf