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Does anyone have any experience with the JetBrains Meta Programming System? Is MPS better than, say, developing a DSL in Ruby?

Federico Tomassetti
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I don't have any personal experience with MPS, but it was mentioned on the recent episode of Herding Code with Markus Völter. Here's my understanding. MPS is a projection editor which means, instead of parsing and editing text, you are directly editing the underlining language data structure. As Markus mentions, MPS allows you to define your own language but you can also introduce new language concepts into existing languages. For example, you can add a new keyword to Java in a matter of minutes. MPS blurs the lines between internal and external DSLs and, with this, you get static typing and tool support which you wouldn't get when developing a DSL with a dynamic language like Ruby.

Ben Griswold
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I work for JetBrains. I led the MPS project for several years, and now I am working on another project which is also completely written in MPS. According to my experience, MPS is worth using :-)

The answer to your question depends on many things. If you have Ruby based system, or want to create a language quickly, Ruby based internal DSL might be the best choice. If you want to generate Java, and have time to learn MPS, MPS might be the best case. You might also consider systems like XText, etc, which are middle ground between Ruby based DSLs and MPS.

Konstantin Solomatov
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MPS is an interesting beast and has a very huge potential. The idea is simply fantastic:

  • Inside an IDE (MPS) the user defines more or less visually his DSL(s)
  • the IDE allows to generate not just the language itself (the runtime or what it does), but also the "tool" aka a more or less full blown IDE, that he or other users can use to edit that new language.

That being said, unfortunately at least for the actual available MPS versions, Jetbrains failed to deliver the above(at least for me) because: - it is very very hard and complicated to use - like it would not have been made by the authors of the easy to use IntelliJ. - there are just too many concepts and "ways" the user needs to learn before it's able to do something useful, and still one gets the feeling of tapping into the dark. - the IDE won't generate an IDE for you but something inside MPS too, a "Cell Based Editor" only (as of this version).

I tried MPS several times (cause the concept is so wonderful and promising), but unfortunately as of this moment I wasn't able to do something useful with it. I might be to stupid for MPS, but in the time I was just figuring out basic about MPS, I was able to deliver fully blown usable Groovy based DSL.

I'm still following MPS's evolution, and hope that one day will deliver what did initially promised, since it's such a fantastic idea.

A. Ionescu
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Macros in common lisp object system CLOS can alter the syntax quite dramatically, MPS is pretty similar to ANTLR, but it comes with a graphical editor. However MPS does not appreciate code fragmenting beyond compile and runtime and hence both MPS and ANTLR convolve around static metaprogramming problems. You still can't create constructs that will accept an arbitrary number of sub-construct arguments like Monadics, eg; a list comprehension builder that takes an arbitrary number of filters and list generators. To make that possible you need to programmatically alter the raw AST. More experienced Lispers can probably point out other transformations that can't be done.

Concepts make sense
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I agree that documentation has been an issue for beginners when learning MPS. This was certainly true when the previous post was written (2010). Having experienced this first-hand, and finally having succeeded in understanding the system, I wrote The MPS Language Workbench (volumes I and II) to help smooth the learning curve. Feedback I get from readers is that the books are sufficient to help you get started (Volume I) and learn more advanced aspects of the MPS platform (Volume II).

Regarding the answer to the original question. Yes, I believe MPS has key advantages compared to developing a DSL in Ruby or Groovy. The reason is that as a language designer you

  1. Have much better control over all aspects of the language,
  2. The languages you build with MPS can include graphical notations and user interface elements, which make them a hybrid between a user interface and a text DSL script/program,
  3. MPS helps migrate programs as you evolve your language (e.g., refactoring or other changes to the language can propagate to the end-users of the languages, using automatic DSL script/program migrations).

You can see a good example of DSL built with MPS in the MetaR project.

Fabien Campagne
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