> This isn’t parser-style backtracking

How is this different from backtracking? You're doing a depth-first search over possible interpretations. The grammar is just expressed in the type system instead of usual spec formats.

Critiques in other comments are accurate. This is a tooling nightmare, but also probably a nightmare to read. Consider an expression like

  2026 March 10 to 13

What's the binding precedence? Does this mean March 10 through March 13, or midnight to 1 PM on March 10th? I think this breaks down outside of trivial examples that are better achieved in other ways.