Re: [Rd] comment causes browser() to exit (PR#9063)

From: Tim Hesterberg <>
Date: Fri 07 Jul 2006 - 17:22:10 GMT

>If I'm not mistaken, this works as documented. ...

Thanks for the response.

The behavior with <return> is as documented -- hence my earlier "enhancement" request.
The behavior with <a comment> is contrary to the documentation, hence this as a "bug" report.

On the second point -- help(browser) says:

     Anything else entered at the browser prompt is interpreted as an R
     expression to be evaluated in the calling environment: ...
whereas the actual behavior is to interpret a comment as equivalent to "c", and to exit the browser.

On the first point -- I would like to argue that the behavior of return (and comments) should be changed, at least as a user option. Here is a typical piece of code from a function; note the use of comments and blank lines to improve readability:

  # If statistic isn't a function or name of function or expression,   # store it as an expression to pass to fit.func.   substitute.stat <- substitute(statistic)   if(!is.element(mode(substitute.stat), c("name", "function")))     statistic <- substitute.stat

  # Get name of data. <- substitute(data)
  if(! <- "data" <-

  # How many observations, or subjects if sampling by subject?   n <- nObservations <- numRows(data) # n will change later if by subject

  # Save group or subject arguments?
  if(is.null(save.subject)) save.subject <- (n <= 10000)   if(is.null( <- (n <= 10000)

If I now stick a browser() in that function, and throw a line at a time from the source file to R, it exits whenever I throw a blank line or comment. I try to remember to skip the blank lines and comments, but I sometimes forget, and get very annoyed when I have to start over.

I could use "c" in some contexts, but not others: * I often want to evaluate code that is not part of the   defined function.
* I sometimes change objects and want to go evaluate some lines   that were previously evaluated.

In the enhancement request I requested an option to turn off the current behavior of return. I personally would just change the default behavior, and have both blank lines and comments do nothing. This is simpler, and people can always use c to quit the browser.

This behavior of browser() is the most annoying thing I've found about using R. As I anticipate using R a lot in the future, I would appreciate very much if it is changed. I spent a fair amount of time trying to see if I could change it myself, but gave up.

Tim Hesterberg

Andy Liaw wrote:
>If I'm not mistaken, this works as documented. As an example (typed
>directly into the Rgui console on WinXP):
>R> f <- function() {
>+ browser()
>+ cat("I'm here!\n")
>+ cat("I'm still here!\n")
>+ }
>R> f()
>Called from: f()
>Browse[1]> ## where to?
>I'm here!
>I'm still here!
>which I think is what you saw. However:
>R> f()
>Called from: f()
>Browse[1]> n
>debug: cat("I'm here!\n")
>Browse[1]> ##
>I'm here!
>debug: cat("I'm still here!\n")
>I'm still here!
>From ?browser:
>(or just return) exit the browser and continue execution at the next
>synonym for c.
>enter the step-through debugger. This changes the meaning of c: see the
>documentation for debug.
>My interpretation of this is that, if the first thing typed (or pasted) in
>is something like a null statement (e.g., return, empty line, or comment),
>it's the same as 'c', but if the null statement follows 'n', then it behaves
> _
>platform i386-pc-mingw32
>arch i386
>os mingw32
>system i386, mingw32
>major 2
>minor 3.1
>year 2006
>month 06
>day 01
>svn rev 38247
>language R
>version.string Version 2.3.1 (2006-06-01)
>> I'm trying to step through some code using browser(),
>> executing one line at a time.
>> Unfortunately, whenever I execute a comment line, the browser exits.
>> I previously reported a similar problem with blank lines.
>> These problems are a strong incentive to write poor code
>> -- uncommented code with no blank lines to improve
>> readability -- so that I can use browser() without it exiting
>> at inconvenient times.
>> Additional detail:
>> (1) I'm running R inside emacs, with R in one buffer and a
>> file containing code in another, using a macro to copy and
>> paste a line at a time from the file to the R buffer.
>> (2) The browser() call is inside a function.
>> Right now the lines I'm sending to the browser are not part
>> of the function, though usually they are.
>> --please do not edit the information below--
>> Version:
>> platform = i386-pc-mingw32
>> arch = i386
>> os = mingw32
>> system = i386, mingw32
>> status =
>> major = 2
>> minor = 3.1
>> year = 2006
>> month = 06
>> day = 01
>> svn rev = 38247
>> language = R
>> version.string = Version 2.3.1 (2006-06-01)
>> Windows XP Professional (build 2600) Service Pack 2.0
>> Locale:
>> LC_COLLATE=English_United States.1252;LC_CTYPE=English_United
>> States.1252;LC_MONETARY=English_United
>> States.1252;LC_NUMERIC=C;LC_TIME=English_United States.1252
>> Search Path:
>> .GlobalEnv, package:methods, package:stats,
>> package:graphics, package:grDevices, package:utils,
>> package:datasets, Autoloads, package:base
>> ______________________________________________
>> mailing list
>Notice: This e-mail message, together with any attachments...{{dropped}} mailing list Received on Sat Jul 08 03:26:50 2006

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