[Haskell-cafe] Extensible Exceptions

[Henning Thielemann]

On Sat, 22 Nov 2008, Thomas Schilling wrote:

> It's a pattern match error, implemented by throwing an asynchronous
> exception.  The idea being, that we only have one mechanism (well, an
> synchronous exceptions, thrown via throwIO).
>
> Yes, I know that there's a difference between "error" and "exception",
> but I would argue that which is which depends on the program.  For
> example, for most programs a pattern match error is a fatal condition,
> there's no sane recovery from it.  OTOH, in a program like GHCi, a
> pattern match error in an executed statement is an exceptional
> condition, which we want to catch, so it doesn't kill GHCi.

It's completely ok to run something in a sandbox and try to observe 
errors. But that's debugging and I think there is no need to do this in 
many places of an application. In general handling errors automatically is 
not possible, because an error might also be if a program loops 
infinitely. Thus one should not generally handle an error like an 
exception.