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"A REPL environment is more of a tool chain issue than a language design issue."

Moreof, maybe, but it is language design, too. If you had a Java REPL, you still would have to type quite a bit of stuff (a class and a function) before you would have your "Hello, world".

Yes, you could add an implicit class named GLOBAL that magically gets a property named 'P' the moment you type

   P = "Hello, world";

but I would call that doing language redesign.

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Actually, I really enjoy using Groovy as a Java REPL, when having to use Java. Your code is run in a Script class

Most java code is valid Groovy code and it has some nice dynamic features, syntax sugar and has closures. I am currently using it to hack together a small DSL to easily configure a transformation from XML -> CSV

Here's an example of a Groovy session (From my instance of IntelliJ IDEA through Tools -> Groovy Console)

  > P = "Hello world!"
  Hello world!
  > sub = P.substring(5)
  world!
  > sub ==~ / wo.+/ ? println("World") : {}()
  World

> Most java code is valid Groovy code

Up to Java 7 you could say "most" but why not "all"? Was it too difficult to test full compatibility? Why is the == slightly different between Java and Groovy, and the rest of the little differences which only confuse? And as for your example it doesn't look in the slightest like Java...

    P = "Hello world!"
    sub = P.substring(5)
    sub ==~ / wo.+/ ? println("World") : {}()

Why wasn't Groovy updated so most java 8 code is also valid Groovy code? And why didn't you actually post some code to do something useful like "configure a transformation from XML -> CSV" instead of creating a HN login to post a meaningless syntax sample?

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