> "If there are no exceptions and you have a function-call control flow, you can enforce that the only types the caller understands from the callee are the type

> "If there are no exceptions and you have a function-call control flow, you can enforce that the only types the caller understands from the callee are the types in the signature." This has historically resulted in either ignoring errors from sub-functions, because their error return type don't map properly, or returning generic "i got an error" without any more information about what the error was. And all this was historically patched over by having verbose log files that could be written to from anywhere and the user had to peruse and try to make sense of after the fact. Some franework tried to create complicated error code (like Windows COM) but in the end there is no free lunch. Errors are hard.