On Thu, Nov 15, 2012 at 08:25:16PM +0100, Axel Svensson wrote:
> > we cannot (as in pil64)
> > simply push the runtime expression onto the stack before the call, and
> > pop it off afterwards.
> How about pushing the expression to a global variable?

This would be easy, but not very useful imho.

At least for me, the main purpose was the backtrace information on
errors, interactively or in the log files. Without that it is often
difficult to figure out where exactly the program crashed, and the
history of calls which lead to that situation.

Until now only the output of (env) was available, which contains the
snapshot of the runtime environment at the point of the crash, but no
history information.

A global variable would hold only the most recent call, like what is
returned by (up).

Also, its semantics would be highly confusing and error prone, because
the variable might be set to another value unexpectedly by intervening
function calls.

- Alex
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