[R] Echoing commands (not using source())

[Henrik Bengtsson]

No, I am actually not thinking about [R] as a macro language. I was thinking
about the "reflection" methods build in into the language, e.g.
Internal(body(fun)). But I guess that it requires the source to be loaded
into the memory, which is not necessary. Is that correct?

Writing the code "twice" using cat(...) makes it easier to do misstakes.
Another idea is to but the whole code into a character string and evaluate
it. That works, but the code won't be parsed until run-time. I think I will
use source() for now. It solves my problem and is also more memory efficient
since the code is only loaded iff the function is called, e.g.

myFunction <- function() {
  source("myFunction.R", echo=TRUE);
}

The problem with this is that it will search for the file in the current
directory, i.e. it won't work within libraries if you don't have some kind
of lookup method such as found in demo() and example().


Thanks

Henrik Bengtsson

> -----Original Message-----
> From: ripley at auk.stats [mailto:ripley at auk.stats]On Behalf Of Prof Brian
> D Ripley
> Sent: Tuesday, April 10, 2001 11:42 PM
> To: Henrik Bengtsson
> Cc: r-help at stat.math.ethz.ch
> Subject: Re: [R] Echoing commands (not using source())
>
>
> On Tue, 10 Apr 2001, Henrik Bengtsson wrote:
>
> > Is there a way of echoing (similar to Matlab "echo on")
> commands that are
> > being executed? I know how to do this for script files by using
> source(...,
> > echo=TRUE), but I would like to be able to use this within
> *any* function. I
>
> One problem is that is not that what source(..., echo = TRUE
> does). It echo
> expressions at the prompt level, but not all commands.  R is not a macro
> language like Matlab.
>
> > am also not looking for the debug() function. Here is what I
> would like to
> > do:
> >
> > myFunction <- function() {
> >   echo(TRUE);
> >   x <- 3;
> >   cat("x = ", x, "\n");
> >   echo(FALSE);
> > }
>
> (That's not really correct R.  Line feeds are command separators as
> well as ;, so you have a lot of empty commands in there.)
>
> > Output:
> > >myFunction()
> > x <- 3;
> > cat("x = ", x, "\n");
> > x = 3
> > >
>
> You can only do this by modifying the function to print the commands,
> as source() does.  Note that by time the function is being evaluated it
> is already parsed, so in a sense there is no `command' to be echoed.
> You can get a rough re-construction via deparse on expressions
> (and a command line can include multiple expressions).
>
> Why do you want to do this? A simple pre-processing of the function
> to be
>
> myFunction <- function() {
>    cat("x <- 3", "\n")
>    x <- 3
>    cat("cat(\"x = \", x, \"\n\"), "\n")
>    cat("x = ", x, "\n")
> }
>
> might be simplest, but I get the impression that you are thinking
> of R as a
> macro language and there may be a more powerful approach to your
> real goal.
>
>
> --
> Brian D. Ripley,                  ripley at stats.ox.ac.uk
> Professor of Applied Statistics,  http://www.stats.ox.ac.uk/~ripley/
> University of Oxford,             Tel:  +44 1865 272861 (self)
> 1 South Parks Road,                     +44 1865 272860 (secr)
> Oxford OX1 3TG, UK                Fax:  +44 1865 272595
>

-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-
r-help mailing list -- Read http://www.ci.tuwien.ac.at/~hornik/R/R-FAQ.html
Send "info", "help", or "[un]subscribe"
(in the "body", not the subject !)  To: r-help-request at stat.math.ethz.ch
_._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._._