Emulate Stata 8 clustered bootstrapped regression - stata

Question

I'm trying to store a series of scalars along the coefficients of a bootstrapped regression model. The code below looks like the example from the Stata [P]rogramming manual for postfile, which is apparently intended for use with such procedures.
The problem is with the // commented lines, which fail to work. More specifically, the problem seems to be that the syntax below worked in Stata 8 but fails to work in Stata 9+ after some change in the bootstrap procedure.
cap pr drop bsreg
pr de bsreg
reg mpg weight gear_ratio
predict yhat
qui sum yhat
// sca mu = r(mean)
// post sim (mu)
end
sysuse auto, clear
postfile sim mu using results , replace
bootstrap, cluster(foreign) reps(5) seed(6112): bsreg
postclose sim
use results, clear
Adding version 8 to the code did not solve the issue. Would anyone know what is wrong with this procedure, and how to fix it for execution in Stata 9+? The problem has been raised in the past and more recently, but without finding an answer.
Sorry for the long description, it's a long problem.
I've presented the issue as if it's a programming one because I'm using this code to replicate some health inequalities research. It's necessary to bootstrap the entire procedure, not just the reg model. I have some quibbles with the methodology, but nothing that would stop me from replicating the analysis.

Answer 1

Adding noisily to the bootstrap showed a problem with the predict command. Here's a fix using a tempvar macro.
cap pr drop bsreg
pr de bsreg
reg mpg weight gear_ratio
tempvar yhat
predict `yhat'
qui sum `yhat'
sca mu = r(mean)
post sim (mu)
end
sysuse auto, clear
postfile sim mu using results , replace
bootstrap, cluster(foreign) reps(5) seed(6112): bsreg
postclose sim
use results, clear