st: -using- option for program executed by -simulate-

[Phil Schumm <pschumm@uchicago.edu>]

Often when performing simulations, it is helpful to start with an  
existing dataset and then add to it, rather than having to create the  
entire dataset from scratch at each iteration.  It would then seem  
logical to pass the location of the saved dataset into one's program  
via the -using- option.  However, for some reason, I can't seem to  
get that to work (as demonstrated by this simple example):


. input group

         group
  1. 0
  2. 1
  3. end

. expand 16
(30 observations created)

. tempfile myfile

. save `"`myfile'"'
file /tmp/S_03268.000001 saved

.
. program foo, rclass
  1.     syntax varname using/, diff(real) sd(real)
  2.     drop _all
  3.     use `"`using'"'
  4.     tempvar y
  5.     gen `y' = `diff'*`varlist' + (invnorm(uniform())*`sd')
  6.     ttest `y', by(`varlist')
  7.     ret scalar p = r(p)
  8. end

.
. simul p = r(p), reps(100): foo group using `"`myfile'"', diff(1) sd(1)
using not allowed
r(101);


I believe this error is being thrown by -_prefix_command-, as called  
from within -simulate-.  Is there a known restriction against using  
the -using- option in this context?


-- Phil

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