Re: [Haskell-cafe] Re: Exception handling in numeric computations

On Fri, 2009-03-27 at 20:38 +0300, Gregory Petrosyan wrote:

On Fri, Mar 27, 2009 at 7:31 PM, Donn Cave wrote:

...

Quoth John Lato ,

...

An exception is caused by some sort of interaction with the run-time system (frequently a hardware issue). The programmer typically can't check for these in advance, but can only attempt to recover after they've happened.

An error is some sort of bug that should be fixed by the programmer.

I have never felt that I really understood that one.

Me too :-)

BTW, John, how often do you encounter _hardware_ issues compared to "errors"?

Can't speak for anyone else, but I usually encounter hardware issues just before I replace the hardware...

Is an "out of memory" thing an error or exception? You will say "exception, for sure", wouldn't you? :-)

No. GHC possesses an out-of-memory exception that (IIRC) it never throws, because it's simply not worth trying to recover from heap exhaustion. Maybe 20 years ago it was, but these days a program that manages to exhaust space is almost certainly either buggy or poorly optimized. An `error' is any condition where the correct response is for the programmer to change the source code :)

And if it is a result of applying known-to-be-very-memory-hungry algorithms to non-trivial input? Looks like programmer's error, doesn't it?

See above.

And I think I can provide lots of similar examples.

If there exists separation between errors and exceptions, it should be very strong and evident — otherwise "casual programmers" like myself will need to stare at the ceiling every time they write something to decide what suits best.

Protip: try pacing instead of staring at the ceiling. jcc