st: different handling if missings in programs using syntax varlist [if}

[Bjorn Van Campenhout <bjorn.vancampenhout@gmail.com>]

Dear statalist,

I have observed different outcomes when I have missing observations in 
programs that use the if qualifier. I was wondering what logic is behind 
this.
Here is a self-contained example:

sysuse auto

replace price=. if foreign==1

cap pro drop foo
pro def foo
  syntax varlist
  gen comment="this is only a test"
end



cap pro drop foobar
pro def foobar
  syntax varlist [if]
  marksample touse
  gen comment="this is only a test" if `touse'
end

foo price
drop comment
foobar price

For those who wonder, I am trying to make a program that reports 
missings and want to be able to use conditions in my function calls.

Kind regards,
Bjorn
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