From rgentlem at fhcrc.org  Sat May 23 18:55:19 2009
From: rgentlem at fhcrc.org (Robert Gentleman)
Date: Sat, 23 May 2009 09:55:19 -0700
Subject: [Rd] [R] step by step debugger in R?
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Hi,
  I stripped the cc's as I believe that all read this list.

Romain Francois wrote:
> [moving this to r-devel]
> 
> Robert Gentleman wrote:
>> Hi,
>>
>> Romain Francois wrote:
>>  
>>> Duncan Murdoch wrote:
>>>    
>>>> On 5/22/2009 10:59 AM, Michael wrote:
>>>>      
>>>>> Really I think if there is a Visual Studio strength debugger, our
>>>>> collective time spent in developing R code will be greatly reduced.
>>>>>         
>>>> If someone who knows how to write a debugger plugin for Eclipse wants
>>>> to help, we could have that fairly easily.  All the infrastructure is
>>>> there; it's the UI part that's missing.
>>>>
>>>> Duncan Murdoch
>>>>       
>>> [I've copied Mark Bravington and Robert Gentleman to the list as they
>>> are likely to have views here, and I am not sure they monitor R-help]
>>>
>>> Hello,
>>>
>>> Making a front-end to debugging was one of the proposed google summer of
>>> code for this year [1], it was not retained eventually, but I am still
>>> motivated.
>>>
>>> Pretty much all infrastructure is there, and some work has been done
>>> __very recently__ in R's debugging internals (ability to step up). As I
>>> see it, the ability to call some sort of hook each time the debugger
>>> waits for input would make it much easier for someone to write
>>>     
>>
>>  I have still not come to an understanding of what this is supposed to
>> do? When
>> you have the browser prompt you can call any function or code you want
>> to. There
>> is no need for something special to allow you to do that.
>>   
> Sure. What I have in mind is something that gets __automatically__
> called, similar to the task callback but happening right before the user
> is given the browser prompt.

 I am trying to understand the scenario you have in mind. Is it that the user is
running R directly and your debugger is essentially a helper function that gets
updated etc as R runs?

 If so, then I don't think that works very well and given the constraints we
have with R I don't think it will be able to solve many of the problems that an
IDE should.  The hook you want will give you some functionality, but no where
near enough.

 Let me suggest instead that the IDE should be running the show. It should
initialize an instance of R, but it controls all communication and hence
controls what is rendered on the client side.  If that is what you mean by
embedding R, then yes that is what is needed. There is no way that I can see to
support most of the things that IDE type debuggers support without the IDE
controlling the communication with R.

 And if I am wrong about what your debugger will look like please let me know.

 best wishes
   Robert


> 
>>> front-ends. A recent post of mine (patch included) [2] on R-devel
>>> suggested a custom prompt for browser which would do the trick, but I
>>> now think that a hook would be more appropriate. Without something
>>> similar to that, there is no way that I know of for making a front-end,
>>> unless maybe if you embed R ... (please let me know how I am wrong)
>>>     
>>
>>  I think you are wrong. I can't see why it is needed. The external
>> debugger has
>> lots of options for handling debugging. It can rewrite code (see
>> examples in
>> trace for how John Chambers has done this to support tracing at a
>> location),
>> which is AFAIK a pretty standard approach to writing debuggers. It can
>> figure
>> out where the break point is (made a bit easier by allowing it to put
>> in pieces
>> of text in the call to browser).  These are things the internal
>> debugger can't do.
>>
>>   
> Thanks. I'll have another look into that.
> 
>>> There is also the debug package [3,4] which does __not__ work with R
>>> internals but rather works with instrumenting tricks at the R level.
>>> debug provides a tcl/tk front-end. It is my understanding that it does
>>> not work using R internals (do_browser, ...) because it was not possible
>>> at the time, and I believe this is still not possible today, but I might
>>> be wrong. I'd prefer to be wrong actually.
>>>     
>>
>>   I don't understand this statement. It has always been possible to
>> work with
>> the internal version - but one can also take the approach of rewriting
>> code.
>> There are some difficulties supporting all the operations that one
>> would like by
>> rewriting code and I think a combination of external controls and the
>> internal
>> debugger will get most of the functionality that anyone wants.
>>
>>   There are somethings that are hard and once I have a more complete
>> list I will
>> be adding this to the appropriate manual. I will also be documenting
>> the changes
>> that I have been making, but that project is in flux and won't be done
>> until the
>> end of August, so people who want to look at it are welcome (it is in
>> R-devel),
>> but it is in development and could change pretty much without notice.
>>   Romain noted that we now support stepping out from one place to another
>> function.  We also have a debugonce flag that lets you get close to
>> step in, but
>> step in is very hard in R.
>>
>>   I am mostly interested in writing tools in R that can be used by
>> anyone that
>> wants to write an external debugger and am not that interested in any
>> particular
>> external debugger. I would be happy to listen to feature requests or
>> issues that
>> arise - but the discussion should probably be on R-devel mailing list.
>>
>>   best wishes
>>     Robert
>>
>>
>>  
>>> Romain
>>>
>>> [1] : http://www.r-project.org/soc09/ideas.html#p5
>>> [2] : https://stat.ethz.ch/pipermail/r-devel/2009-April/053128.html
>>> [3] : http://cran.r-project.org/web/packages/debug/index.html
>>> [4] : http://cran.r-project.org/doc/Rnews/Rnews_2003-3.pdf
>>>
>>>     
>>
>>   
> 
> 

-- 
Robert Gentleman, PhD
Program in Computational Biology
Division of Public Health Sciences
Fred Hutchinson Cancer Research Center
1100 Fairview Ave. N, M1-B514
PO Box 19024
Seattle, Washington 98109-1024
206-667-7700
rgentlem at fhcrc.org



[Rd] [R] step by step debugger in R?
Robert Gentleman