Macro expansion in a while loop

[kkranker]

I'm having a little trouble with macro expansion inside a while loop. As a toy example, the following code gives me an error message:

set obs 10
local i = 1
local xx noisily
while `i' < 5 {
  cap `xx' {
      gen a`i' = runiform() in 1/9
  }
  local i = `i' + 1  
}

Here's the error message I get with Stata 15.1:

. set obs 10
number of observations (_N) was 0, now 10

. local i = 1

. local xx noisily

. while `i' < 5 {
  2.   cap `xx' {
  3.       gen a`i' = runiform() in 1/9
  4.   }
  5.   local i = `i' + 1  
  6. }
(1 missing value generated)
(1 missing value generated)
(1 missing value generated)
(1 missing value generated)
} is not a valid command name
r(199);

For what it's worth, the same code runs fine without the macro:

set obs 10
local i = 1
while `i' < 5 {
  cap noisily {
      gen a`i' = runiform() in 1/9
  }
  local i = `i' + 1  
}

Has anyone run into this issue, or something like it, before? If so, what is incorrect with my code? Or is this a Stata bug?

Thanks!

[Clyde Schechter]

Very strange. I can replicate the problem on my setup as well.

I also note that if instead of using -while- to control the loop we do

clear
set obs 10
local i = 1
local xx noisily
forvalues i = 1/4 {
    cap `xx' {
        gen a`i' = runiform() in 1/9
    }
}

there is no error generated. And no error if I replace the -forvalues- with a -foreach i of numlist- loop.

So I think this is a Stata bug. You might want to send this to Tech Support.

[Andrew Musau]

There was a similar discussion previously, see the logic in #9.

https://www.statalist.org/forums/for...preted-wrongly

[Clyde Schechter]

Very interesting. Thank you, Andrew, for pointing up the prior discussion.

[kkranker]

Thanks Andrew for pointing out the old discussion. (I had looked at old forums but obviously didn't use the right search terms.) I still find this behavior odd and unexpected, and I wonder why this doesn't come up more often and why it can't be fixed. But I guess Stata knows about this and it's the intended behavior.

[Bjarte Aagnes]

This issue is reported to Tech Support with reference to this discussion.