Let's say I have a super-wonderful new programming language, and I want there to be an IDE for it. What IDE platform/framework could I use to get this done efficiently? I mean things like:

• Collection of files in a project, searching them, tabbed/split editors etc. — the basics.
• Syntax highlighting and auto-indent/reformatting.
• Providing the user interface for code completion — hit tab, get a list (I'll have to implement the necessary partial evaluation myself (it's a dynamic language)). This is the feature I'm most wishing for.
  • Built-in parser framework which is good at recovering from the sort of syntax errors occurring in code that is in the middle of being edited would be helpful.
• In-editor annotation of syntax/runtime error locations fed back from the language runtime.
• REPL (interactive evaluator) interaction with the same completion as in the editor.

This system should be Linux/Mac/Windows cross-platform (in that priority order). Being implemented in Java (or rather, accepting language plugins written in Java) is possibly useful, but anything else is worth a try too.