Re: GHCi debugger status

Pepe Iborra wrote:

On Mon, Nov 24, 2008 at 2:03 PM, Peter Hercek wrote:

...

Maybe what Claus means is that he would like to see the dynamic stack and be able to traverse it and at each location in the dynamic stack he could investigate the free variables in the expression (corresponding to the dynamic stack slot). I actually considered this as a feature request but I decided that I would like to have this implemented sooner: http://hackage.haskell.org/trac/ghc/ticket/2737

As long as you start with :trace, you can see the dynamic stack with :history, and traverse it with :back. At any point in the stack the free variables are available, or so I believe. What is the missing feature you would like to request in this case?

Hmmm, I believe that dynamic stack is not the same as :trace history. The point is that the trace history shows all the evalueated expressions as they occure in time. But dynamic stack shows only the expressions which evaluation did not finish yet. Example: 1 let fn a = 2 let f x = x + 1 in 3 case f a of 4 1 -> "one" 5 _ -> "" When selected expression is "one" then the trace will contain something like this (just doing it from the top of my head): line 1-5 fn a = ... line 3-5 case f a of ... line 3 f a line 2 let f x = x + 1 in line 2 x + 1 possibly something from outside which forces x and consequently a line 4 "one" But the dynamic stack would contain: line 1-5 fn a = ... line 3-5 case f a of ... line 4 "one" The difference is that the dynamic stack contains only the items which computation is not finished yet. The stuff which was already reduced to a final value is not there any more. This way you could trace the dynamic stack back to see what arguments was your function called with since the arguments must be free variables in the expression which called your function of interest. Of course the same information is in the trace too ... that is if your trace history is long enough and you are willing to search it manually. That is the rason for ticket 2737. I do not want to search it manually! Maybe trace is the dynamic stack and I did not realize what trace contains till now. That would be kind of a shame :-D Peter.