On 11-04-09 3:51 PM, Paul Johnson wrote:
Years ago, I did lots of Perl programming. Perl will let you be lazy
and write functions that refer to undefined variables (like R does),
but there is also a strict mode so the interpreter will block anything
when a variable is mentioned that has not been defined. I wish there
were a strict mode for checking R functions.
Here's why. We have a lot of students writing R functions around here
and they run into trouble because they use the same name for things
inside and outside of functions. When they call functions that have
mistaken or undefined references to names that they use elsewhere,
then variables that are in the environment are accidentally used. Know
what I mean?
dat<- whatever
someNewFunction<- function(z, w){
#do something with z and w and create a new "dat"
# but forget to name it "dat"
lm (y, x, data=dat)
# lm just used wrong data
}
I wish R had a strict mode to return an error in that case. Users
don't realize they are getting nonsense because R finds things to fill
in for their mistakes.
Is this possible? Does anybody agree it would be good?
It would be really bad, unless done carefully.
In your function the free (undefined) variables are dat and lm. You
want to be warned about dat, but you don't want to be warned about lm.
What rule should R use to determine that?
(One possible rule would work in a package with a namespace. In that
case, all variables must be found in declared dependencies, the search
could stop before it got to globalenv(). But it seems unlikely that
your students are writing packages with namespaces.)
Duncan Murdoch
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