R devel - Feb 2013 - Running R scripts with interactive-style evaluation

Hi,

when running a R-script like this:

enable_magic()
compute_stuff()
disable_magic()

the whole script is parsed into a single expression and then evaluated, whereas
when using the interactive shell after each line entered, a REPL loop happens.

Is there a way to make a script evaluation behave like this, because I need a
single REPL iteration for every expression in the script.

It doesn't matter if it's a source()-like way or "R CMD BATCH"
or even feeding stdin to R or whatever...

Regards,

Marc

On 13-02-26 5:07 AM, Marc Aurel Kiefer wrote:
> Hi,
>
> when running a R-script like this:
>
> enable_magic()
> compute_stuff()
> disable_magic()
>
> the whole script is parsed into a single expression and then evaluated,
whereas when using the interactive shell after each line entered, a REPL loop
happens.
It's actually a vector of expressions that are evaluated one at a time, 
but close enough...
> Is there a way to make a script evaluation behave like this, because I need
a single REPL iteration for every expression in the script.
You don't say why you need that.  From your subject line, I'm guessing 
you want to do something like a user prompt, then wait for user input, 
then another user prompt, etc.? So the fact that disable_magic() was 
parsed at the beginning shouldn't matter.  Or does it?
>
> It doesn't matter if it's a source()-like way or "R CMD
BATCH" or even feeding stdin to R or whatever...
I think it all depends on what kind of input users are allowed to type, 
but basically this is something you'll need to write yourself, I don't 
think any of the normal running modes of R will suit you.  Take a look 
at the source to source() or to the Sweave-related functions for ideas.

Duncan Murdoch

Which part of the read-eval-print loop loop ("REPL loop") do you need?

source(file, print=TRUE) gives you the printing part, which is what I usually
want.

Opening a file connection and repeatedly calling parse(n=1) gives you the read
part,
  > tf <- tempfile()
  > cat(file=tf, sep="\n", "x <- 1 +", "10 ; y
<- 2:7", "10:3")
  > f <- file(tf, open="rt")
  > parse(f, n=1)
  expression(x <- 1 + 10)
  > parse(f, n=1)
  expression(y <- 2:7)
  > parse(f, n=1)
  expression(10:3)
  > parse(f, n=1)
  expression()
  > close(f)
and you can copy the code from source() to get the eval and print stuff right.

Bill Dunlap
Spotfire, TIBCO Software
wdunlap tibco.com

> -----Original Message-----
> From: r-devel-bounces at r-project.org [mailto:r-devel-bounces at
r-project.org] On Behalf
> Of Marc Aurel Kiefer
> Sent: Tuesday, February 26, 2013 2:08 AM
> To: r-devel at r-project.org
> Subject: [Rd] Running R scripts with interactive-style evaluation
> 
> Hi,
> 
> when running a R-script like this:
> 
> enable_magic()
> compute_stuff()
> disable_magic()
> 
> the whole script is parsed into a single expression and then evaluated,
whereas when
> using the interactive shell after each line entered, a REPL loop happens.
> 
> Is there a way to make a script evaluation behave like this, because I need
a single REPL
> iteration for every expression in the script.
> 
> It doesn't matter if it's a source()-like way or "R CMD
BATCH" or even feeding stdin to R
> or whatever...
> 
> Regards,
> 
> Marc
> 
> ______________________________________________
> R-devel at r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel

If you're intending to run some code that may require user input, then I
share your need. I started two threads on this some time ago [1,2], but as
far as I know it still isn't possible. My workaround is to use
"expect", or
to create a temporary .Rprofile if that is not available, from within a
shell script wrapper (see [3], lines 197-221). It isn't pretty, and I'd
love to see support for this kind of use case in R proper (happy to
contribute my time to help if someone with better knowledge of the R source
could guide me), but it's the best solution I've found.

All the best,
Jon

--
[1] https://stat.ethz.ch/pipermail/r-help/2008-January/150786.html
[2] https://stat.ethz.ch/pipermail/r-devel/2008-September/050803.html
[3] https://github.com/jonclayden/tractor/blob/master/bin/tractor#L197



On 26 February 2013 10:07, Marc Aurel Kiefer <marcaurelkiefer@gmx.de>
wrote:
> Hi,
>
> when running a R-script like this:
>
> enable_magic()
> compute_stuff()
> disable_magic()
>
> the whole script is parsed into a single expression and then evaluated,
> whereas when using the interactive shell after each line entered, a REPL
> loop happens.
>
> Is there a way to make a script evaluation behave like this, because I
> need a single REPL iteration for every expression in the script.
>
> It doesn't matter if it's a source()-like way or "R CMD
BATCH" or even
> feeding stdin to R or whatever...
>
> Regards,
>
> Marc
>
> ______________________________________________
> R-devel@r-project.org mailing list
> https://stat.ethz.ch/mailman/listinfo/r-devel
>
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