In the mean time you could have student run the following code each time (put
it into .Rprofile or something) until they learn good coding practices:
testfunc <- function(expr, value, ok, visible) {
tmp <- deparse(expr)
if( grepl( '<- *[0-9.]+ *[])&|]', tmp ) ) {
warning(' You used "<-" in the above expression,\nit was
interpreted as an assignment\nif you wanted a comparison, use a space between
the "<" and the "-"')
}
TRUE
}
addTaskCallback( testfunc )
you might want to change the warning to cat (and add \n), or extend the regular
expression logic to other cases, or ...
But if nothing else getting the warning will reinforce that parens/spaces are a
good idea if only to avoid the computer complaining. The problem is I can
think of some false positives that I have not worked out yet how to avoid.
--
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.s...@imail.org
801.408.8111
> -----Original Message-----
> From: r-devel-boun...@r-project.org [mailto:r-devel-boun...@r-
> project.org] On Behalf Of ivo welch
> Sent: Tuesday, August 24, 2010 9:03 AM
> To: phgrosj...@sciviews.org
> Cc: r-devel@r-project.org
> Subject: Re: [Rd] small syntax suggestion
>
> hi ted, philippe, and others---I agree with everything you write about
> good coding practice. none of us would be writing x<-3, even when
> we want to assign 3. we know better. we would at least use a space,
> if not a paren. alas, my suggestion is not so much for you. It is
> trying to spare novices that are just beginning to use R some
> unnecessary frustration. I bet that most of us have made this
> mistake at least once.
>
> to the extent that it requires a token "<-[0-9]" to recognize this, it
> could be an easy special case/warning/error. to the extent that it
> requires more, it is probably not worth the hassle.
>
> [I am a great fan of syntax checking. I am not a great fan of many
> but the simplest recycling rules (from 1 to N) BY DEFAULT. It's just
> asking for trouble.]
>
> regards,
>
> /iaw
> ----
> Ivo Welch (ivo.we...@brown.edu, ivo.we...@gmail.com)
>
>
>
>
> On Mon, Aug 23, 2010 at 4:27 PM, Philippe Grosjean
> <phgrosj...@sciviews.org> wrote:
> > I tell to my students that it is very important (not only for
> legibility) to
> > place spaces between operands. They have to write such a code like
> this:
> >
> > if (x < -3) do_something
> >
> > That way, there is no ambiguity. Don't you think it's important to
> write
> > clear code, including by using spaces where it makes it easier to
> read,...
> > and less ambiguous, as you just realize?
> >
> > Best,
> >
> > Philippe Grosjean
> >
> > On 23/08/10 19:06, Davor Cubranic wrote:
> >>
> >> On 2010-08-23, at 6:15 AM, Barry Rowlingson wrote:
> >>
> >>> On Sun, Aug 22, 2010 at 4:33 PM, ivo welch<ivo.we...@gmail.com>
> wrote:
> >>>>
> >>>> I have found that my students often make the mistake of
> >>>> mixing up comparisons and assignments with negative numbers:
> >>>>
> >>>> if (x<-3) do_something;
> >>>
> >>> If you tell your students not to use '<-' for assignment, then they
> >>> can't make this mistake, because = for assignment has additional
> >>> restrictions on it:
> >>
> >> The students are trying to *compare* to a negative number, and trip
> on R's
> >> parsing of "<-". They could use '=' for assignment all they want
> (which I
> >> thought is being discouraged as a code style these days, BTW), and
> they'll
> >> still run into this problem.
> >>
> >> Davor
> >> ______________________________________________
> >> R-devel@r-project.org mailing list
> >> https://stat.ethz.ch/mailman/listinfo/r-devel
> >>
> >>
> >
>
> ______________________________________________
> R-devel@r-project.org mailing list
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