> > The implementation is just something like
>
> > addIOErrorLocAndPath loc path io
> > = catch io (\err -> ioError err{loc=loc,path=path})
>
> This reminds me of _scc_:
>
> 1) We're annotating the code with programmer-meaningful annotations
> which are then used at runtime to help them understand program
> behaviour.
>
> 2) It has the same nested behaviour as _scc_
>
> 3) Just as stacks of cost centres are useful for profiling, it'd be
> useful to have stacks of error locations.
> When you print an IOError, you'd get a list of (nested) error
> locations - it'd feel a lot like the stack dumps you get from
> Java.
Right, but there's another issue here: we don't particularly want to
expose the names of functions in the innards of the I/O library when we
generate an IOError. The only piece of information that it of any use
to a consumer of the library is the function that he/she called.
The full stack trace is of course highly useful when debugging a
library, though. In GHC, you *can* get the stack trace info when an
exception is raised - you have to compile the program with profiling and
-auto-all, and then run it with +RTS -xc (I think). We've also
considered having a programatic interface to enable the CCS to be
captured and treated as a first class object in Haskell, but we haven't
got around to implementing it yet.
Cheers,
Simon
