Determining response variable in a formula

dat<-data.frame(x=rnorm(10),y=rnorm(10),z=rnorm(10))
my.form <- as.formula(y ~ x + z)
my.form

m<-model.frame(my.form,data=dat)
model.extract(m,"response")

I have a formula from which I want to deduce the name of the response
variable. One way of doing so is as follows:

my.form <- as.formula("y ~ x + z")
all.vars(my.form)[1]

[1] "y"

Is there a better way and/or preferrred method of determining "y" from
my.form than this one? In messing around with terms, I came up with:

all.vars(terms(my.form))[attr(terms(my.form), "response")]

[1] "y"

But that seems too ugly to be best.

Thanks,

Dave Kane

R.version

        _                
platform i686-pc-linux-gnu
arch     i686             
os       linux-gnu        
system   i686, linux-gnu  
status                    
major    2                
minor    1.0              
year     2005             
month    04               
day      18               
language R