Claus Reinke wrote:
No, it's a real problem. If we retained all the variables in scope at
every breakpoint, GHCi would grow a whole bunch of space leaks. It's
pretty important that adding debugging shouldn't change the space
behaviour of the program. Of course, constant factors are fine, but
we're talking asymptotic changes here.
Now perhaps it would be possible to arrange that the extra variables
are only retained if they are needed by a future breakpoint, but
that's tricky (conditional stubbing of variables), and :trace
effectively enables all breakpoints so you get the space leaks back.
Then how about my suggestion for selectively adding lexical scope to
breakpoints? I'd like to be able to say
:break <loc/name> {names}
and have GHCi make the necessary changes to keep {names} available
for inspection when it hits that breakpoint.
The only easy way to do that is to recompile the module that contains the
breakpoint. To do it without recompiling is about as hard as doing what I
suggested above, because it involves a similar mechanism (being able to
selectively retain the values of free variables).
Cheers,
Simon
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