Simon Marlow wrote:
One idea that occurred to us recently is this: GHCi could provide a simplified version of the cost-centre-stack machinery *all the time*, giving you a proper backtrace for any exception, at least for the parts of the call stack that are interpreted. We don't care about the cost too much - interpreted code is a lot slower than compiled already, and it would only be a small constant factor. I think this would be a huge win for debuggability. And a nice project for anyone who wants to hack on the GHC internals - though not a small task by any means.
The cost-centre machinery is very close to the machinery necessary to generate the trace of the Haskell tracer Hat. If you implement one, with small modifications you get the other. The overhead for both is basically the same, except that the larger Hat trace needs to be written to file. Ciao, Olaf