[fanf2]

Yes, modern query-oriented compilers (such as TypeScript and C# Roslyn) keep the AST in memory and co-operate closely with the editor via the language server protocol.

I recently saw an example of a language that aims to be AST-first rather than notation-first: it serialises to XML! http://mbeddr.com/

[baq]

Nothing modern about it, lisp has been doing it for fifty years now. S-exprs also serialize to xml quite nicely ;)

[fanf2]

In a query-oriented compiler, you can give it a source location and ask for type infomation, or where is the definition of the symbol at that location, and the compiler will do just enough work to give you the answer, using laziness and memoization to make it reasonably efficient. As far as I know, LISP systems don't work that way: they parse and evaluate (and maybe compile) as soon as an expression is entered, without the kind of laziness you see in a query-oriented compiler.

This recent link was pretty good, I think https://ollef.github.io/blog/posts/query-based-compilers.htm... and this discussion with Anders Hejlsberg https://youtu.be/wSdV1M7n4gQ