On Mon, Nov 24, 2008 at 5:28 PM, Daniil Elovkov
Peter Hercek wrote:
Daniil Elovkov wrote:
A refinement of :tracelocal could be :tracedirect (or something) that would save the history not anywhere within the given function but only within parents, so to say. For example,
This looks like what I thought of as searching for values in dynamic stack (explained in my response to Pepe Iborra in this thread).
Yes, first when I saw that your message I also thought "Hey, Peter has already suggested it!" :)
But now I see that we're talking about slightly different things. Consider
fun x y = let f1 = ... (f2 x) ... -- f1 calls f2 f2 = exp_f2 in ...
Now, if we're at exp_f2 then 'dynamic stack' in your terminology includes (f2 x) since it's the caller and all f1 as well.
On the other hand, :tracedirect that I suggested would not include f1, as it's not a direct ancestor. And for the purpose of binding variables which are syntactically in scope, it is indeed not needed. :tracedirect would be sufficient.
Also, I think that :tracedirect can be easily implemented based only on simple syntactic inclusion relation.
I am not convinced this would not imply the same problems as simply storing all the variables in scope at a breakpoint. Consider this slightly more contorted example: fun x y = let f1 = ... (f2 x) ... -- f1 calls f2 f2 x = x * 2 in case x of 1 -> f2 0 _ -> f2 (f1 y) g x = let z = (some complex computation) in z `div` x main = print (g (fun 1 2)) This is a classical example of why laziness gets in the way of debugging. Now, when (f2 0) gets finally evaluated and throws a divByZero error, x and y are nowhere to be found. Since we do not have a real dynamic stack, it is difficult to say where their values should be stored. The only place I can think of is at the breakpoint itself, but then as Simon said this poses a serious efficiency problem.