Parsing is not sufficient for new languages, it needs semantics as well.

For example inferred types need semantics like type evaluation of expressions, for example C++ `auto f = 1 + 1.0;` has to know the semantics of mixed type arithmetic `1 + 1.0` to get the result type as `float` and then bind that type to `f`. New languages like Julia and Rust and Go, many functional languages like Haskell and Ocaml and retrofits to languages like C++ and Java provide capabilities like this.

Type evaluation of expressions requires full knowledge of visibility, what parts of the system libraries and user code is visible at the point of `set(a, 1);` to decide which `set()` function is going to be called (there are lots of `set()` functions in libraries and user code), and so what the return type is, so it can be used in `auto a1 = set(a, 1);` as the type of `a1`.

It needs more than a parser to perform these computations. The current technology solving it is the Language Server Protocol which is a way for the IDE to send the work to a separate process that contains most of the compiler except the code generation so the workload of a compiler does not interrupt the UI. Many language projects are providing LSP compliant servers, like clangd from the clang C/C++ compiler project or gopls from the Go language project.

There is work in progress to integrate such servers with Geany.