[Caml-list] How useful do you find the OCaml debugger?

[Caml-list] How useful do you find the OCaml debugger?

[donna+spam]

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Hello,

My advisor and I were having a dicussion about the utility of debuggers for
functional langugages. He was of the opinion that they are not very useful
at all (for a functional language), and wondered if anyone even uses, for
instance, the OCaml debugger. Based on google-ing I have done, it looks like
it *is* used, but it's hard to get a good impression from just a web crawl.
So:

- Do you personally find the OCaml debugger useful?

- Is there any sort of general opinion in the OCaml community about the
debugger?

Thanks!

- Donna

[This is a re-post, since I wasn't sure it worked the first time. My
apologies if you've seen this already.]

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Jean-Christophe Filliatre]

donna+spam@cs.cmu.edu writes:
 > 
 > My advisor and I were having a dicussion about the utility of debuggers for
 > functional langugages. He was of the opinion that they are not very useful
 > at all (for a functional language), and wondered if anyone even uses, for
 > instance, the OCaml debugger. Based on google-ing I have done, it looks like
 > it *is* used, but it's hard to get a good impression from just a web crawl.
 > So:
 > 
 > - Do you personally find the OCaml debugger useful?
 > 
 > - Is there any sort of general opinion in the OCaml community about the
 > debugger?

I agree: the ocaml debugger is not very useful because usually if your
ocaml code compiles it is correct :-)

I've used  the ocaml debugger  a few times,  however, and it  is quite
nice.  Navigating in  the source  under Emacs  and the  ability  to go
backward is really great. I never spent more than a few minutes inside
the debugger.  The ocaml debugger also  has a few  drawbacks. Code for
pretty-printers have  to be loaded  as a separate  code and this  is a
pain:  the  ocaml  debugger  tries  to load  all  the  needed  modules
recursively but often fails doing  so (because there is a .mli without
a .ml, a module hidden into  some library, etc.) It would be much more
easy to  use pretty-printers from  the code you're debugging,  even if
the  debugger  has to  load  it twice,  since  you  usually have  some
pretty-printers for  your abstract data  types. It would be  even more
useful if the  debugger could print the values  in abstract data types
(we don't need abstraction anymore, we are in the debugger).

My  impression is  that  the  ocaml debugger  is  not fully  debugged,
probably  because the  ocaml team,  as  most of  us, does  not need  a
debugger at all :-)

-- 
Jean-Christophe

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Thomas Fischbacher]

On Wed, 4 Feb 2004, Jean-Christophe Filliatre wrote:

> I agree: the ocaml debugger is not very useful because usually if your
> ocaml code compiles it is correct :-)

If that is true, than the problems you are tackling are too simple to 
be really interesting. :->

-- 
regards,               tf@cip.physik.uni-muenchen.de              (o_
 Thomas Fischbacher -  http://www.cip.physik.uni-muenchen.de/~tf  //\
(lambda (n) ((lambda (p q r) (p p q r)) (lambda (g x y)           V_/_
(if (= x 0) y (g g (- x 1) (* x y)))) n 1))                  (Debian GNU)

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[Caml-list] Re: How useful do you find the OCaml debugger?

[Jan Kybic]

> - Do you personally find the OCaml debugger useful?

Yes, very useful. Obviously a well written code reduces the need for a
debugger somehow, but once in a while you forget something and then it
is useful to see what the program is doing and compare it with what
you think it should be doing. I often insert debugging prints but 
sometimes it is faster to use the debugger, depends on the nature of
the problem.

Concerning the OCaml debugger, I have only used it for a few times, so
I am perhaps not the ideal judge. However, I loved the ability to go
backward. On the other hand, I would like to see some of the abilities
of the toploop integrated in it - evaluating arbitrary expressions,
like it can be done in the Python debugger, for example.

Jan


-- 
-------------------------------------------------------------------------
Jan Kybic <kybic@ieee.org>                  tel. +420 2 2435 7264
       or <kybic@fel.cvut.cz>,     http://cmp.felk.cvut.cz/~kybic

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Richard Jones]

On Tue, Feb 03, 2004 at 11:31:33PM -0500, donna+spam@cs.cmu.edu wrote:
> Hello,
> 
> My advisor and I were having a dicussion about the utility of debuggers for
> functional langugages. He was of the opinion that they are not very useful
> at all (for a functional language), and wondered if anyone even uses, for
> instance, the OCaml debugger. Based on google-ing I have done, it looks like
> it *is* used, but it's hard to get a good impression from just a web crawl.

Sounds like your advisor never had a real job :-)

Debuggers are very useful indeed for tracking down logic bugs in real
world (ie. large, convoluted, badly written) programs.

I've found ocamldebug to be very painful to use, compared to, say,
gdb.  That's when it works at all.  For reasons I don't really
understand I've found that ocamldebug doesn't work very reliably,
often showing the wrong line numbers or losing the connection to the
debugged process.

One of the features I'd really like to see for ocaml would be proper
support for stabs / gdb.  At the moment I'm mainly relying on
inserting eprintf / prerr_endline into the code.

Rich.

-- 
Richard Jones. http://www.annexia.org/ http://www.j-london.com/
Merjis Ltd. http://www.merjis.com/ - improving website return on investment
If I have not seen as far as others, it is because I have been
standing in the footprints of giants.  -- from Usenet

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Pierre Boulet]

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Hello,

one feature of ocaml that is very useful also is the ability to trace 
some functions in the toplevel. When debugging code, I usually start by 
tracing some functions and if it doesn't work, I use the debugger. I 
specially like the ability to go backwards as it really helps tracking 
down exception raising points. Just let it run until the exception is 
raised and step backwards to examine the environment just before it is 
raised.

But I agree with some previous posters that I seldom use it because my 
code usually simply works :-)

Cheers,

-- 
Pierre Boulet

<http://www.lifl.fr/~boulet/>
Tél : (+33)6.09.08.18.11

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Christophe Raffalli]

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I have use a lot the debuggers, but veru often without succes because:

- my program was to complex to debug it without backtracking
- backtracking often crashes (but it is hard to reproduce) and moreover 
is not usable when performing IO (at least the last time I used it)

If would be nice to have two ml functions (to use inside your code to 
debug):

allow_debugback (): backtraking is allowed after this function is 
executed (create the first fork for backtracking there). This function 
could recieve the maximum number of fork in argument instead of unit.

disallow_debugback (): no more backtracking possible (kills all the 
previous forks)

I think this is simple to implement and not very hard to use (for 
instance it is easy to put such a function in the treatment part of a 
parser to solve the IO problems).


-- 
Christophe Raffalli
Université de Savoie
Batiment Le Chablais, bureau 21
73376 Le Bourget-du-Lac Cedex

tél: (33) 4 79 75 81 03
fax: (33) 4 79 75 87 42
mail: Christophe.Raffalli@univ-savoie.fr
www: http://www.lama.univ-savoie.fr/~RAFFALLI
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Re: [Caml-list] How useful do you find the OCaml debugger?

[Kip Macy]

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Speaking of backtracking, not too long ago I wrote a process
checkpoint/restore facility for DragonFly BSD. I believe that it
was ported to FreeBSD and I know that a superset of its functionality
was implemented for Linux by LLNL. It seems, at least on the surface of
things, that this could be tied into ordinary debuggers like GDB to
provide simple backtracking by checkpointing a process every n seconds,
where n is a function of the size of the process and how recently one
wants to roll back to. This would be nice to have for many languages not
just ocaml - plus many people would like to use native code.

				-Kip


> I have use a lot the debuggers, but veru often without succes because:
>
> - my program was to complex to debug it without backtracking
> - backtracking often crashes (but it is hard to reproduce) and moreover
> is not usable when performing IO (at least the last time I used it)
>
> If would be nice to have two ml functions (to use inside your code to
> debug):
>
> allow_debugback (): backtraking is allowed after this function is
> executed (create the first fork for backtracking there). This function
> could recieve the maximum number of fork in argument instead of unit.
>
> disallow_debugback (): no more backtracking possible (kills all the
> previous forks)
>
> I think this is simple to implement and not very hard to use (for
> instance it is easy to put such a function in the treatment part of a
> parser to solve the IO problems).
>
>
> --
> Christophe Raffalli
> Université de Savoie
> Batiment Le Chablais, bureau 21
> 73376 Le Bourget-du-Lac Cedex
>
> tél: (33) 4 79 75 81 03
> fax: (33) 4 79 75 87 42
> mail: Christophe.Raffalli@univ-savoie.fr
> www: http://www.lama.univ-savoie.fr/~RAFFALLI
> ---------------------------------------------
> IMPORTANT: this mail is signed using PGP/MIME
> At least Enigmail/Mozilla, mutt or evolution
> can check this signature
> ---------------------------------------------
>

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Henri Dubois-Ferriere]

> I've found ocamldebug to be very painful to use, compared to, say,
> gdb.  That's when it works at all.  For reasons I don't really
> understand I've found that ocamldebug doesn't work very reliably,
> often showing the wrong line numbers or losing the connection to the
> debugged process.

i have only used the debugger a few times, because each time i ran into 
similar problems as those listed above.

henri

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Damien Doligez]

On Wednesday, February 4, 2004, at 11:36 AM, Henri Dubois-Ferriere 
wrote:

>> I've found ocamldebug to be very painful to use, compared to, say,
>> gdb.  That's when it works at all.  For reasons I don't really
>> understand I've found that ocamldebug doesn't work very reliably,
>> often showing the wrong line numbers or losing the connection to the
>> debugged process.
>
> i have only used the debugger a few times, because each time i ran into
> similar problems as those listed above.

It would help if you guys could file proper bug reports (with specific
and reproducible examples) on such problems.  Please use
< http://caml.inria.fr/bin/caml-bugs >.

-- Damien

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Nuutti Kotivuori]

donna wrote:
> My advisor and I were having a dicussion about the utility of
> debuggers for functional langugages. He was of the opinion that they
> are not very useful at all (for a functional language), and wondered
> if anyone even uses, for instance, the OCaml debugger. Based on
> google-ing I have done, it looks like it *is* used, but it's hard to
> get a good impression from just a web crawl.  So:
>
> - Do you personally find the OCaml debugger useful?

Yes, very. Especially in OCaml for its ability to step backwards as
well as forwards in the program execution. And I use it in completely
functional code.

Personally I'd say that I use the OCaml debugger more often for OCaml
code than gdb for C code - but less often than I use the perl debugger
for perl code.

> - Is there any sort of general opinion in the OCaml community about
> the debugger?

I have no idea.

-- Naked

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Damien Doligez]

On Wednesday, February 4, 2004, at 05:31 AM, <donna+spam@cs.cmu.edu> 
wrote:

> - Do you personally find the OCaml debugger useful?

I use it from time to time to debug the O'Caml compiler and the
runtime.  It's so much fun using both ocamldebug and gdb on the same
process that I almost wish there were more bugs in O'Caml :-)

It would be really hard to work without it.  The O'Caml compiler
is definitely not in the "when it typechecks, it works" category.


> - Is there any sort of general opinion in the OCaml community about the
> debugger?

 From the answers you've got so far, it seems clear that there is
no consensus.

-- Damien

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Ken Rose]

donna+spam@cs.cmu.edu wrote:
> Hello,
> 
> My advisor and I were having a dicussion about the utility of debuggers for
> functional langugages. He was of the opinion that they are not very useful
> at all (for a functional language), and wondered if anyone even uses, for
> instance, the OCaml debugger. Based on google-ing I have done, it looks like
> it *is* used, but it's hard to get a good impression from just a web crawl.
> So:
> 
> - Do you personally find the OCaml debugger useful?

My biggest ocaml program is a DSL compiler that's about 6000 lines long, 
and has been gradually written over the past 5 years or so.  I've been 
pretty good about placing assertions in the code - particularly 
"assert(false)" in branches that I don't believe should be taken.  This 
has been very helpful, because when the world proves my opinion wrong, 
which it often does, I can just run in the debugger until the assertion 
trips, and then back up until I see what happened to produce the 
situation I thought was impossible.

  - ken

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Re: [Caml-list] How useful do you find the OCaml debugger?

[Issac Trotts]

On Tue, Feb 03, 2004 at 11:31:33PM -0500, donna+spam@cs.cmu.edu wrote:
> Hello,
> 
> My advisor and I were having a dicussion about the utility of debuggers for
> functional langugages. He was of the opinion that they are not very useful
> at all (for a functional language), and wondered if anyone even uses, for
> instance, the OCaml debugger. Based on google-ing I have done, it looks like
> it *is* used, but it's hard to get a good impression from just a web crawl.
> So:
> 
> - Do you personally find the OCaml debugger useful?

Yes, definitely.  The ability to run programs in reverse is especially
useful.  Using it, I removed a bunch of bugs from my Delaunay
triangulator yesterday.  It would have been much harder to find the
problems some other way.

That said, the debugger would be even better if it had conditional
breakpoints, the ability to change variable values, and the ability to
call functions.  

-- 
Issac Trotts
http://redwood.ucdavis.edu/~issac

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Re: [Caml-list] How useful do you find the OCaml debugger?

[_JusSx_]

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On Tue, Feb 03, 2004 at 11:31:33PM -0500, donna+spam@cs.cmu.edu wrote:
> Hello,
> 
> My advisor and I were having a dicussion about the utility of debuggers for
> functional langugages. He was of the opinion that they are not very useful
> at all (for a functional language), and wondered if anyone even uses, for
> instance, the OCaml debugger. Based on google-ing I have done, it looks like
> it *is* used, but it's hard to get a good impression from just a web crawl.
> So:
> 
> - Do you personally find the OCaml debugger useful?
> 
> - Is there any sort of general opinion in the OCaml community about the
> debugger?
> 
> Thanks!
> 
> - Donna
> 
> [This is a re-post, since I wasn't sure it worked the first time. My
> apologies if you've seen this already.]


I fiund thant debugging single function in the toplevel is more usefull
than using ocaml debugger.

Bye
 

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