Assignment for an array element fails in a loop

[evertrol]

I have this simple procedure

pro testarray
  a = dblarr(2)
  k = 1
  for j = 0, 2 do begin
     print, j
     if j eq k then a[1] = -1
     print, a
     ind = where(a lt 0, /null)
     print, ind
     a[ind] = 0
     print, a
  endfor
end

When I run this (gdl -X -e testarray), the output is

       0
       0.0000000       0.0000000
!NULL
       0.0000000       0.0000000
       1
       0.0000000      -1.0000000
           1
       0.0000000      -1.0000000
       2
       0.0000000      -1.0000000
           1
       0.0000000      -1.0000000

which is not what I expect: the -1 should be changed to 0, and only show up once in the output.

If I change k to 2, similar incorrect behaviour happens. But if I change k to 0, the expected/correct behaviour happens (i.e., -1 shows up only once in the output).

If I remove the loop (and the j eq k condition), I also observe the correct behaviour.

I don't know if I'm missing something here, or whether this is an actual bug in GDL. (I am not able to test this behaviour with IDL.)

My set up is a Macbook Pro M1, Sonoma 14.6.1 (Darwin 23.6.0), running a self-installed GDL in the terminal (iTerm), with the GDL version given as GDL - GNU Data Language, Version v1.1-30-g35d32bbc.

[alaingdl]

Thanks for the clear report. Two bad news :

• I succeed to reproduce the problem, on x86_64 :(
• I absolutely not understood what happen :(