R devel - Sep 2008 - R --interactive and readline() creates infinite loop

Dear all,

I have asked before, in R-help [1], about a way to create an  
interactive session in which commands are taken from a file or  
standard input - like R CMD BATCH but additionally allowing user input  
- but there was no response to that question, and the workarounds that  
I have found (using "expect", creating a temporary .Rprofile) are ugly
and problematic.

With the appearance of the --interactive flag in R 2.7.0 I thought  
this might become possible, but it not only does not behave as I would  
expect, it appears to go into an infinite loop, and uses 100% CPU  
until killed.

$ echo 'print(readline("Input:"))' | R --no-save --quiet
 > print(readline("Input:"))
Input:[1] ""
 >
[no interactivity]

$ echo 'print(readline("Input:"))' | R --no-save --quiet
--interactive
[no response at all]

This behaviour remains in the latest alphas of R 2.8.0. My platform is  
Mac OS X.5.5 on Intel Core 2 Duo.

I assume, given this outcome, that this is not the intended use of -- 
interactive, but I still wonder if there is any way to achieve an  
interactive session based on a predefined set of commands without  
writing a completely new front-end (overkill, surely?).

Any guidance would be appreciated.

Regards,
Jon

[1] http://finzi.psych.upenn.edu/R/Rhelp02a/archive/117412.html


--
Jonathan D. Clayden, Ph.D.
Research Fellow
Radiology and Physics Unit
UCL Institute of Child Health
30 Guilford Street
LONDON  WC1N 1EH
United Kingdom

t | +44 (0)20 7905 2708
f | +44 (0)20 7905 2358
w | www.homepages.ucl.ac.uk/~sejjjd2/

For an alternative approach to your original goal, take a look at 
demoSource() in the SoDA package from CRAN.  It's a bit tedious to set 
up (see the Details section of the help file) but uses standard R 
sessions to mix lines from a demo file and interactive input.

John

Jon Clayden wrote:
> Dear all,
>
> I have asked before, in R-help [1], about a way to create an 
> interactive session in which commands are taken from a file or 
> standard input - like R CMD BATCH but additionally allowing user input 
> - but there was no response to that question, and the workarounds that 
> I have found (using "expect", creating a temporary .Rprofile) are
ugly
> and problematic.
>
> With the appearance of the --interactive flag in R 2.7.0 I thought 
> this might become possible, but it not only does not behave as I would 
> expect, it appears to go into an infinite loop, and uses 100% CPU 
> until killed.
>
> $ echo 'print(readline("Input:"))' | R --no-save --quiet
> > print(readline("Input:"))
> Input:[1] ""
> >
> [no interactivity]
>
> $ echo 'print(readline("Input:"))' | R --no-save --quiet
--interactive
> [no response at all]
>
> This behaviour remains in the latest alphas of R 2.8.0. My platform is 
> Mac OS X.5.5 on Intel Core 2 Duo.
>
> I assume, given this outcome, that this is not the intended use of 
> --interactive, but I still wonder if there is any way to achieve an 
> interactive session based on a predefined set of commands without 
> writing a completely new front-end (overkill, surely?).
>
> Any guidance would be appreciated.
>
> Regards,
> Jon
>
> [1] http://finzi.psych.upenn.edu/R/Rhelp02a/archive/117412.html
>
>
> -- 
> Jonathan D. Clayden, Ph.D.
> Research Fellow
> Radiology and Physics Unit
> UCL Institute of Child Health
> 30 Guilford Street
> LONDON  WC1N 1EH
> United Kingdom
>
> t | +44 (0)20 7905 2708
> f | +44 (0)20 7905 2358
> w | www.homepages.ucl.ac.uk/~sejjjd2/
>
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>

> I assume, given this outcome, that this is not the intended use of
> --interactive, but I still wonder if there is any way to achieve an
> interactive session based on a predefined set of commands without writing a
> completely new front-end (overkill, surely?).
When you say an interactive session, do you mean that the output
should be identical to what would have happened if you had copied and
pasted the code in to an R session?  I'm working on some code that
allows you to do this, based around parse and eval.

Hadley

-- 
http://had.co.nz/