On May 4, 2010, at 12:31 , Gregory Crosswhite wrote:
On May 4, 2010, at 5:22 AM, John Lato wrote:
"Crashing at the point of the error" isn't necessarily useful in Haskell due to lazy evaluation. The code will crash when the result of the partial function is evaluated, which may be quite far away (in terms of function calls) from where the programmer would expect.
But hypothetically, suppose that you decided to use safeSecondElement anyway; now you have to deal with a Nothing in your code. Since, again, you don't know how to recover from this (as if you did, you wouldn't have gotten a Nothing in the first place), the only thing you can do is propagate it through the calculation, until it reaches someone who can recover from it, which means that now your whole calculation has to be muddled up with Maybe types wrapping every result purely to capture the
Using Maybe as a monad helps a lot here.
possibility of a bug (or hardware fault, I suppose). If your program relied on this calculation, then it *still* has no choice but to terminate, and it *still* doesn't know where the error occurred
It occurs to me that combining Error and Writer gives you traceback. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] allbery@kf8nh.com system administrator [openafs,heimdal,too many hats] allbery@ece.cmu.edu electrical and computer engineering, carnegie mellon university KF8NH