I think it is because of mainstream languages are all prose-first and don't expose the underlying graph structure in useful way for visual editor to manipulate.

I think it is because of mainstream languages are all prose-first and don't expose the underlying graph structure in useful way for visual editor to manipulate. Closest I know are: * paredit/parinfer for Lisps are actually tree editors in disguise. * DRAKON. Having put critical business logic in it, was really a boon for quick understanding after returning to the codebase later.