4 ms·

What are you going to do with the errors once you have collected them? What is the point of sorting or grouping them?

• jstimpfle 8y ago
  A simple example from the compiler I'm working on right now: I output type errors of expressions sorted by their location in the source file, instead of in the order they are detected. I also don't error out on the first one, but find all at once. I could also group warnings and errors together, output only the first N errors, or... whatever I fancy. Errors are just data.
  • gdy 8y ago
    Well, this example seems somewhat contrived to me because these errors are not the errors happening in the compiler, they are diagnostic messages describing the errors in the input data. Any chance you have another example?
    • jstimpfle 8y ago
      "An error happening in the compiler". What's that? If you mean a bug detected, then it should be handled with abort().
      • gdy 8y ago
        An error related to the file system, for example.
        • jstimpfle 8y ago
          A file system error isn't an error happening in the compiler. The file system is an external system. So this error isn't really any different than a syntax error or type error. I would not treat it differently except making a different error message. Of course you cannot parse a file you cannot read, so there is a dependency which means that sooner or later you need to "act" on the error.
          • gdy 8y ago
            Well, grouping errors in your example makes sense when all of them happened during processing a particular input which is expected to be invalid sometimes. Could you share another example where accumulating errors makes sense?
            • jstimpfle 8y ago
              You can do it with anything. Analyze all the files in a directory, for instance. Do all the IO in parallel and merge the results at a central point. Some files might be corrupt or whatever. Merge the results at a central point. Only then present them to the user in a sensible order. A real life example: Asynchronous webservers usually have worker threads for I/O. I/O errors need to be routed to the originators of the I/O requests (which are in other threads). Exceptions cannot do that. Here's the general point: Whether any given thing is an "Error" is highly subjective and context dependent. But clearly the error is data, so why take away the possibility to process it like any other data?
              • gdy 8y ago
                This is an interesting conversation for me, but I still don't quite understand your reasoning. IMO, using exceptions doesn't preclude treating errors as data. In your example with parallel processing, you could throw an error as exception, let it unwind the whole stack, catch it and return as the result of the task. This way you don't couple the code that does the useful work with the code that handles errors. In other words, I don't understand why you dislike exceptions. IMO they are a good tool for any task that doesn't require different actions to handle different errors.
                • jstimpfle 8y ago
                  Exceptions are not just data, at least not if you do not always catch them immediately (in which case they are just pointless). They introduce additional control paths which are hard to reason about. In many languages these are not even explicit. Exceptions require an additional syntax to handle them. And having exceptions requires significant language infrastructure and comes with a huge toll on the structure of software projects. See my topmost comment. > In your example with parallel processing, you could throw an error as exception, let it unwind the whole stack, catch it and return as the result of the task. Which would catch only the first encountered error per thread. And not catch all the other errors that we could encounter and report after that.