JVM scripting languages review

I've been playing around with groovy for the last couple of weeks and I have to say that I am intrigued by it. In the beginning, when I was starting to hear that there was a Groovy JSR that was aiming to create a standard Java scripting language, I was a bit skeptical : I've been using Jython for the last couple of years for the same puprose and so far it has been working out great for me. I already have a number of working application at work that are doing great. I even bought the "Jython for Java programmers" book a few years ago and it was an excellent guide in getting started. Additionally, in the last few months I've been getting back into the same book on the more advanced topics such as embedding jython in other applications (I even have a little prototype NetBeans plugin that is a live Jython interpeter, very nice in exploring the NetBeans APIs)

So, I said that Jython was generally working well for me for the same purpose. However, I did have a couple of things that bug me about it:
- Because Jython is an implementation of Python on top of a JVM, it is forced (or at least expected) to move at the same speed that python does. So, although Jython works pretty well for JVM scripting and and is generally feature complete, since it's a couple of releases behind Python proper, there is a lot of pressure to keep up with the language. Since one of the reasoning for using Jython is that you can either reuse python skills on the JVM, that really doesn't translate very well since Jython cannot use Python features implemented natively. Thus the "python skills transfer" thing doesn't really work.

- Although I really like the Python newline handling and indentation, it is kinda messed up that it's difficult to use python inside web pages or directly from the command line ('cause you have to maintain and respect the white space, which works great inside a regular script but it sucks when you try to do something like "jython 'for i in os.listdir("."):\n print i\n \n'"... which could have been so much better if there was another delimiter

- Because Jython has to implement the Python APIs, for a java developer to use Jython (e.g. because of the concise syntax or scripting features) he/she has to learn the totally new Python syntax and libraries (although Java most likely has equivalent APIs, using the Java APIs is not consice).

So, back to Groovy. I was initially a bit cynical, since Jython was really doing it for me (for the most part). I remember reading how the Groovy APIs were so unstable, and that it wasn't particularly catching on.. After all, I was a faithful Jython user.

So, one day I decided to give it a shot, and now, after reading about it, I am starting to really like it. For the most part, it appears to have all the goodness of Jython (e.g. concise map or list syntax, etc), however, without having to learn a totally new API. It enhances and improves Java and the JVM (e.g. Grails is really doing some really interesting things on top of Hibernate with GORM). It has a whole bunch of "best-of-breed" features taken from Ruby and Perl, without having to comply with a particular formal specification that isn't particularly Java related (e.g. such as the Python spec). It has Java-like syntax and delimiters and Java code could be used "as is" inside Groovy. Additionally, talking about syntax, it can be used nicely from the command like as in "groovy 'for i in [1,2,3] { print i }" - assuming that the for loop is correct.

All in all, so far Groovy has been really nice. I am really looking forward to the Groovy in Action book coming out so that I can dig more into it. The only thing that I really miss from Jython so far is the interactive console. I mean that Groovy that have a graphical groovy shell that can be used to execute Groovy statements, however, each statement is executed as a separate script and the results of the statements do not build up inside the script context (which might be easily fixable, but so far I don't know enough about it to fix it right off the bat).