A Guile debugger workgroup?

[Olivier Dion via "Developers list for Guile, the GNU extensibility library" <guile-devel@gnu.org>]

Greetings Guilers,

There's been a discussion on the state of debugging with Guile on the
guix-devel mailing list.  Here's the relevant link if you want the full
discussion:
<https://lists.gnu.org/archive/html/guix-devel/2022-11/msg00283.html>
which is a reply to <https://issues.guix.gnu.org/issue/58812#id=33>.

I'm going to resume what I've gather here.  I've mainly cutoff Guix
related stuff.  I'm also putting names here for the sake of clarity.

I think it would be interesting to have more inputs from the Guile users
at large -- outside of Guix -- on that topic.  From my personal
experience and the echo I get back from other users, the debugging
experience in Guile is frustrating.

Things I've gather in this reading and on the IRC with other users.
This is by no way a wish list, but simply ideas to improve the debugging
experience:

  1. Documentation on debugging should be improved.  e.g. The `pk`
     procedure.

  2. A tutorial on how to debug a project with `pk` and the REPL.

  3. A single-step (instruction and line) debugger.

  4. Integration in GDB.  e.g. GDB could insert breakpoints in Scheme
     code.

  5. Maybe not make a debugger with a paradigm for language like C but
     instead take inspiration from other Scheme implementation like
     Racket.

Resume start here:

zimon:

  Preparing some materials for introducing Guile to GuixHPC folk, I am
  trying to collect some tips and, if I am honest, the debugging
  experience with Guile is really poor; compared to others (as Python).
  For example, DrRacket provides an easy and nice user experience

  Well, IMHO, we are somehow suffering from some Guile limitations and
  improvements in this area are an hard task.

Maxim:

  I also agree!  It's hard to convince people to pick Guile for their
  project when there is:

  1. Lack of a debugger that can break and step anywhere in your source
     code
     
  2. Lack of debugger integration to an IDE (it's not even integrated
     into Emacs)

  Perhaps we should assemble a Guile debugger workgroup that'd review
  what's broken, what's missing, what can be borrowed from other Scheme
  or languages for inspiration

Ludo:

  Well, Guile has a debugger that lets you do that [...] Geiser is not
  Visual Studio™ but it does a good job.

  Also, [...] I mentioned before that I almost never use breakpoints on
  Guile code [...]  because it’s rarely the right tool for the job.

  I believe this is largely due to (1) writing functional code, and (2)
  doing live programming at the REPL.  Why would you use breakpoints
  when you can just call the relevant procedures on some input to see
  how they behave?

  So I think you won’t convince people to pick Guile for their project
  by selling it as a C/C++/Python drop-in replacement.  Guile is about
  functional programming and live coding so the set of tools differs.

  Despite what I wrote, I think it’s a good idea.  I suppose inspiration
  would come from other Schemes, in particular Racket, and perhaps from
  other live-coding systems (Common Lisp, Smalltalk, etc.), rather than
  from Python or C.

Zimon:

  Maybe I am wrong or miss some Guile features.  From my experience, the
  issue is not the way that the information is presented or how we
  interact with it (Geiser or else) but, instead, the issue is the
  availability of such information.

  Well, so you are using the good ol’ way putting ’pk’ here or there,
  right?  One thing when debugging is to inspect the current state of
  the program; [...] And, ’pk’ is the poor man breakpoint. :-)

  Racket is an example of functional programming and live coding.
  Haskell is another; it is functional programming and if I might, I
  would recommend to give a look at the interactive GHCi debugger

Maxim:

  When searching for how the debugger work in the Guile Reference info
  manual, I also don't find anything useful: only the gut of the
  debugging API of the Guile VM appears to be documented ("Debugging
  Infrastructure"), so documentation is another place that could be
  improved, with some examples and pro tips for real life, practical
  debugging with Guile.

Ludo:

  I think we should identify scenarios where things don’t work as
  expected, and then turn them into bug reports, documentation issues,
  or any other concrete action we should take.

  [...] that brings us back to Maxim’s suggestion of starting a
  debugger workgroup.

Attila:

  [C]oming from common lisp [...], [I] think the lowest hanging fruit in
  the guile debugging experience is making sure that backtraces are not
  cut short when printed.

  [T]his is regularly causing me frustration when all i need to make
  progress is in the cut off part of the backtrace, and the code in
  question is in a part of the codebase that i can't easily change to
  add some good old printf's.

Joshua:

  Just my 2 cents, I always thought that the elisp debugging experince
  is super user friendly and awesome!

  M-x edebug-defun RET function-name RET

  And you are golden!

  It would be awesome if guile could offer something as seemless.

Csepp:

  Can we also get a profiler like Python's Scalene?  I'm pretty sure
  there are some performance bottlenecks it could help identify, both in
  Guix and in Guile itself.

-- 
Olivier Dion
oldiob.dev