Debugging with GHCi.

[Malcolm Wallace]

Simon Marlow <simonmarhaskell at gmail.com> wrote:

> Another part of our vague debugging plan was to add a cheap form of 
> cost-centre stacks to the byte code interpreter, so that you could 
> always get a backtrace at a breakpoint or an exception.  We don't know
> what this "cheap form of CCS" would look like, though.

I do!  It would look a lot like a cut-down version of the Hat trace
format.

You might be interested to know that one of our PhD students has
implemented a full Hat-trace-generator as a modification of the nhc98
and yhc bytecode interpreters.  Initial performance results show that
bytecode runs only about 2-3x slower with tracing turned on.  This is a
big improvement on Hat's original source-to-source transformation method
which gave a slowdown of 50x.

Regards,
    Malcolm