This is a hard question to answer. In general the emphasis changed from getting the compiler to work, and to generate efficient code, to using the technology to

This is a hard question to answer. In general the emphasis changed from getting the compiler to work, and to generate efficient code, to using the technology to implement a rich set of libraries (feedback into compiler), and then writing some simple tools (feedback into libraries and compiler). Probably the single biggest feature was the introduction of Haskell style type classes as a way to systematically provide "generic" features like comparisons and conversions to string which are de rigueur in dynamically typed scripting languages. Less obvious but quite important was switching the parser from Ocamlyacc to Dypgen combined with OCScheme, which together put the grammar in user space, allowing almost the entire grammar to be put in the library. A lot of new features were added with very little or no change to the compiler by just adding some EBNF grammar and suitable Scheme action code to the parser. This can be very effective. For example, with only one extra term in the compiler, I added a dynamic object system that looks a lot like Java with objects and interfaces including "implements" and "extends" stuff. It just uses records of closures (the compiler mod added record extension), but the syntax is neat and almost immediately I used it to factor the webserver into separately compiled plugins. I originally implemented this as a kind of joke, to show off the expressive power in respect of Domain Specific Sub-Languages, but not intended for use. The joke was on me :)