OK, so I finished my first preliminary "type checker" in Rust, but I have excluded control flow analysis as I am planning to target JavaScript.
Type checker, or "verifier", as you may prefer to call it.
https://github.com/whackengine/sdk/tree/master/crates/verifier/src/verifier
I have only tested AS3 expressions in the past; now I have everything from AS3, except that I ignore framework metadata for now as I don't have a framework implemented for now, as well as MXML. (the Event metadata is implemented, though.)
I bet the verifier is working, but I have not tested it yet.