function works (boot.stepAIC ) but throws an error

I realized a strange behavior today with in my R code. I tried a package {boot.StepAIC} which includes a bootstrap function for the results of the stepwise regression with the AIC. However I do not think the statistical background is here the problem (I hope so).
I can use the function at the top level of R. This is my example code.

require(MASS)
require(boot.StepAIC)

n<-100
x<-rnorm(n); y<-rnorm(n,sd=2); z<-rnorm(n,sd=3); res<-x+y+z+rnorm(n,sd=0.1)
dat.test<-as.data.frame(cbind(x,y,z,res))
form.1<-as.formula(res~x+y+z)
boot.stepAIC(lm(form.1, dat.test),dat.test) # should be OK - works at me

However, I wanted to wrap that in an own function. I pass the data and the formula to that function. But I get an error within boot.stepAIC() saying:

the model fit failed in 100 bootstrap samples Error in strsplit(nam.vars, ":") : non-character argument

# custom function
fun.boot.lm.stepAIC<-function(dat,form) {
  if(!inherits(form, "formula")) stop("No formula given")
  fit.lm<-lm(formula=form,data=dat)
  return(boot.stepAIC(object=fit.lm,data=dat))
 }
fun.boot.lm.stepAIC(dat=dat.test,form=form.1)
# results in an error

So where is the mistake? I suppose it must have something to do with the local and global environment, doesn't it?

Using do.call as in anova test fails on lme fits created with pasted formula provides the answer.

boot.stepAIC doesn't have access to form when run within a function; that can be recreated in the global environment like this; we see that lm is using form.1 as the formula, and removing it makes boot.stepAIC fail.

> form.1<-as.formula(res~x+y+z)
> mm <- lm(form.1, dat.test)
> mm$call
lm(formula = form.1, data = dat.test)
> rm(form.1)
> boot.stepAIC(mm,dat.test)
# same error as OP

Using do.call does work. Here I use as.name as well; otherwise the mm object carries around the entire dataset instead of just the name of it.

> form.1<-as.formula(res~x+y+z)
> mm <- do.call("lm", list(form.1, data=as.name("dat.test")))
> mm$call
lm(formula = res ~ x + y + z, data = dat.test)
> rm(form.1)
> boot.stepAIC(mm,dat.test)

To apply this to the original problem, I'd do this:

fun.boot.lm.stepAIC<-function(dat,form) {
  if(!inherits(form, "formula")) stop("No formula given")
  mm <- do.call("lm", list(form, data=as.name(dat)))
  do.call("boot.stepAIC", list(mm,data=as.name(dat)))
}    
form.1<-as.formula(res~x+y+z)
fun.boot.lm.stepAIC(dat="dat.test",form=form1)

This works too but the entire data set gets included in the final output object, and the final output to console, as well.

fun.boot.lm.stepAIC<-function(dat,form) {
  if(!inherits(form, "formula")) stop("No formula given")
  mm <- do.call("lm", list(form, data=dat))
  boot.stepAIC(mm,data=dat)
}    
form.1<-as.formula(res~x+y+z)
fun.boot.lm.stepAIC(dat=dat.test,form=form.1)