Why exceptions for error handling is so important

[Walter Bright via Digitalmars-d]

On 1/11/2015 5:06 AM, Dicebot wrote:
> What is your opinion of approach advertised by various functional languages and
> now also Rust? Where you return error code packed with actual data and can't
> access data without visiting error code too, compiler simply won't allow it.

It's a great question. I have a lot of experience with error codes, and with 
exceptions. I have zero with the packed scheme, though that doesn't stop me from 
having an opinion :-)

Perhaps I misunderstand, but given A calls B calls C,

    A => B => C

and C detects an error, and A knows what to do with the error. B then becomes 
burdened with checking for the error, invoking some sort of cleanup code, and 
then propagating it.

Wouldn't this be uglifying B's source code?

With exceptions, C throws, A catches, and B's cleanup happens automatically.

This matters very much for pipeline style programming (i.e. ranges and algorithms).