Re: Source level debug?

On Sat, Oct 25, 2008 at 12:05 PM, Andreas Thiele <[email protected]> wrote:
> I have a lengthy function which produces an error. Is there a change to see, where in
> the source the error occurs?
>
> At the moment I only understand, that the function is responsible for the error.
> Unfortunately I have no clue where in this lengthy function the error is.

There is a wealth of documentation at:
  http://www.franz.com/support/documentation/8.1/doc/debugging.htm

Here are two ideas I use most myself: first, look at the stack trace
leading to the error using the :zoom and :loc commands. Second,
improve the clarity of the stack trace by running the function
interpreted instead of compiled.

Here's an example interaction, where first function foo is compiled
and called leading to an error. The first :zoom (or :zo) command lists
the stack tracem says the error is somewhere in 'foo. Assuming I'm
very dense and don't understand the error yet ;) I run the same
function interpreted, and it shows the exact division operation that
goes wrong.

In interpreted code even let forms and such are visible as frames in
the stack trace. Couple this with :loc showing the local variables of
the frame, and pinpointing the errors is usually straightforward.

Hope this helps,
- Willem


cl-user(1): (defun foo (x)
                 (/ 3 x))
foo
cl-user(2): (compile 'foo)
foo
nil
nil
cl-user(3): (foo 0)
Error: Attempt to divide 3 by zero.
  [condition type: division-by-zero]

Restart actions (select using :continue):
 0: Return to Top Level (an "abort" restart).
 1: Abort entirely from this (lisp) process.
[1] cl-user(4): :zo
Evaluation stack:

   (error division-by-zero :operation ...)
 ->(foo 0)
   [... excl::%eval ]
   (eval (foo 0))
   (tpl:top-level-read-eval-print-loop)
   (tpl:start-interactive-top-level
      #<terminal-simple-stream [initial terminal io] fd 0/1 @
        #x10115bca>
      #<Function top-level-read-eval-print-loop> ...)
[1] cl-user(5): :res
cl-user(6): (defun foo (x)
                 (/ 3 x))
foo
cl-user(7): (foo 0)
Error: Attempt to divide 3 by zero.
  [condition type: division-by-zero]

Restart actions (select using :continue):
 0: Return to Top Level (an "abort" restart).
 1: Abort entirely from this (lisp) process.
[1] cl-user(8): :zo
Evaluation stack:

   (error division-by-zero :operation ...)
 ->(/ 3 0)
   (foo 0)
   (eval (foo 0))
   (tpl:top-level-read-eval-print-loop)
   (tpl:start-interactive-top-level
      #<terminal-simple-stream [initial terminal io] fd 0/1 @
        #x10115bca>
      #<Function top-level-read-eval-print-loop> ...)
[1] cl-user(9): :loc
Interpreted lexical environment:
x: 0
Compiled lexical environment:
0(required): number: 3
1(rest): excl::more-numbers: (0)
2(local): x: 0
3(local): excl::local-0: (0)
4(local): excl::local-1: 3
5(local): excl::local-2: (0)