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

[Prof Brian Ripley]

On Wed, 11 Apr 2001, Henrik Bengtsson wrote:

> 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?

There's a trick.  The code is kept attached to the function for
user-written code.  Try

> attr(myFunction, "source")
[1] "function() {"
[2] "source(\"myFunction.R\", echo=TRUE);"
[3] "}"


> Writing the code "twice" using cat(...) makes it easier to do misstakes.

I did say `pre-processing': of course R can do it for you, rather easily.

> 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);
> }

Hrmm. You are still writing incorrect R!

> 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
> >
>
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-- 
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

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