Errors happen when one or more of a function’s assumed dependencies are missing or invalidated. So in a PL like you’re imagining, every function would need to run an assertion prologue validating all of its static dependencies. As for dynamic dependencies, they would need to be dynamically (continually) validated, probably at multiple scopes (who watches the watchmen?). If you squint your eyes you will see that static dependency checking is in fact partially provided by type systems, the more capable the type system the broader it’s functional coverage. The complexity actually lies in those dynamic dependencies, which are external systems and components, sitting at the other end of some channel, and this includes the very hardware components the function is running on. If you follow this rabbit hole you’ll see that there’s no such things as static dependencies, just allegedly more stable dynamic ones; and that all dependencies are intertwined with each other within the continuum of the universe; and that anything that works is a miracle, built upon hopes and dreams. So we could say that the ultimate exception is a program working as intended, every time. So why even bother programming defensively? Let it crash!