Re: [Haskell-cafe] Errors in non-monadic code

I agree that whether to use exceptions or not is a very debatable subject and it is a grey area. Still, in your Python example, I would like to point out that just because something is common, it does not mean it is the right thing to do. For example, something that some Java programmers were doing a lot was to loop through an array and, instead of using a counter, they were catching the array out of bounds exception. This is clearly not the right thing to do! But I would like to see more code move away from exceptions and into types like "Maybe" or "Either" or other types defined for the particular situation (as some people were suggesting in the beginning of the thread). And the reason for this it is because when you program against types you have to make a decision whether to handle the error or let it bleed through: you can't ignore the choice because you can't ignore the type. On the other hand, with exceptions, you can easily forget to handle the exception if you're not looking at the documentation at the time when you write the code. Jose On Mon, Aug 19, 2013 at 01:12:13PM -0700, Donn Cave wrote:

jabolopes@google.com, MIME-Version: 1.0 Content-type: text/plain; charset=UTF-8 In-Reply-To: References:

quoth Brandon Allbery,

...

Even in IO, exceptions should be reserved for truly exceptional conditions (of the "program cannot safely continue" variety), not merely for error checking when this can be described as a normal flow of evaluation. Exceptions are not simply alternative flow of control, even in procedural languages; they are *disruptions* of flow of control.

I think that would be debatable, especially as applied to procedural languages in general. It's very common to use exceptions in routine flow of control in Python programs, if I remember right. Meanwhile, the Haskell library in my opinion somewhat weakens your case by making ordinary conditions into exceptions, for example end-of-file.

In the end it's a large grey area. Ideally, what the program has to do, or whether it can even continue at all, is determined by the program using information reported by the function that encounters the error. If there's a good reason why exceptions should be used only when the program won't be able to continue, it must be that the language's exception handling facililty isn't very robust.

Donn

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