A problem with glm() and possibly model-using functions in general?

So, consider the following:

example(glm)
g = function(model) { w = runif(9);glm(model,weights=w); }
g(counts ~ outcome + treatment)

Error in eval(expr, envir, enclos) : object "w" not found

Huh?! I suspect that somebody is lazily evaluating arguments in the
wrong environment (probably GlobalEnv in this case). I'm willing to
accept the fact that there's some mysterious reason you'd actually
want this behavior, but this looks like it should be filed as a bug
to me.

On Fri, 18 Nov 2005, Byron Ellis wrote:

So, consider the following:

example(glm)
g = function(model) { w = runif(9);glm(model,weights=w); }
g(counts ~ outcome + treatment)

Error in eval(expr, envir, enclos) : object "w" not found

Huh?! I suspect that somebody is lazily evaluating arguments in the
wrong environment (probably GlobalEnv in this case). I'm willing to
accept the fact that there's some mysterious reason you'd actually
want this behavior, but this looks like it should be filed as a bug
to me.

Yes, there is a reason you'd actually want this behaviour, and
it is documented. In help(model.frame) it says

      All the variables in 'formula', 'subset' and in '...' are looked
      for first in 'data' and then in the environment of  
'formula' (see
      the help for 'formula()' for further details) and collected  
into a
      data frame.

In your example the environment of 'formula' is the global  
environment,
since that's where it was created.

There isn't a set of scoping rules for formulas that will make  
everyone
happy, but this lexical scope is what R has done for quite some time.

 	-thomas