[R] function arguments: name of an object vs. call producing the object?

[Michael Friendly]

In a function, say foo.glm for glm objects I want to use the name of the 
object as a label for some output,
but *only* if a glm object was passed as an argument, not a call to 
glm() producing that object.
How can I distinguish these two cases?

For example, I can use the following to get the name of the argument:

foo.glm <- function(object) {
    oname <- as.character(sys.call())[2]
    oname
}

 > indep <- glm(Freq ~ mental + ses, family = poisson, data = Mental)
 > foo.glm(indep)
[1] "indep"

But in foo.glm() I want to avoid using this as oname:
 > foo.glm(glm(formula = Freq ~ mental + ses, family = poisson, data = 
Mental))
[1] "glm(formula = Freq ~ mental + ses, family = poisson, data = Mental)"

Here is Mental, if it matters.

 dput(Mental)
structure(list(ses = structure(c(1L, 1L, 1L, 1L, 2L, 2L, 2L,
2L, 3L, 3L, 3L, 3L, 4L, 4L, 4L, 4L, 5L, 5L, 5L, 5L, 6L, 6L, 6L,
6L), .Label = c("1", "2", "3", "4", "5", "6"), class = c("ordered",
"factor")), mental = structure(c(1L, 2L, 3L, 4L, 1L, 2L, 3L,
4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L, 4L, 1L, 2L, 3L,
4L), .Label = c("Well", "Mild", "Moderate", "Impaired"), class = 
c("ordered",
"factor")), Freq = c(64L, 94L, 58L, 46L, 57L, 94L, 54L, 40L,
57L, 105L, 65L, 60L, 72L, 141L, 77L, 94L, 36L, 97L, 54L, 78L,
21L, 71L, 54L, 71L)), .Names = c("ses", "mental", "Freq"), row.names = 
c(NA,
-24L), class = "data.frame")

-- 
Michael Friendly     Email: friendly AT yorku DOT ca 
Professor, Psychology Dept.
York University      Voice: 416 736-5115 x66249 Fax: 416 736-5814
4700 Keele Street    http://www.math.yorku.ca/SCS/friendly.html
Toronto, ONT  M3J 1P3 CANADA