Julia - Broken If statement in while loop? - debugging

Question

I am currently trying to constantly check a condition inside an infinite while loop. I am breaking out of the loop with a few conditionals. However, the while loop is immediately breaking and a debugging println() shows that the code is inside of the first if() statement. Hoover, the preceding line was never run and the if statement needs that information (polar) to compute. I only get an error when trying to call polar later in the program and it does not exist. It is as if that line has been entirely skipped.
Here is the while loop in question:
prevSize = 0
sec = 0
n = 5
while true # wait unit the polar file is done changing
polar = readdlm(polarPath,Float64,skipstart = 12)
if polar[end,1] > aEnd - aStep
println("Done writing polar file")
break #File is fully loaded
else #check every n seconds for stable file size
sleep(1)
global sec += 1
if prevSize == filesize(polarPath) && sec == n
println("Polar file could not converge for all AoA")
break # after n seconds if filesize is constant then use current polar
elseif sec >= n
global sec = 0 # reset sec every n seconds
end
global prevSize = filesize(polarPath)
end
end
The program prints out "Done writing polar file" which means that it used the first break. However, polar was never initialized as a variable and separately calling polar[end,1] > aEnd - aStep gives the expected error of no variable called polar. So my question is how can the code have skipped over the line defining polar and then evaluated an if statement that it does not have the information for?

Answer 1

Here is a simple example of how scoping rules work when using a while loop.
First example, using while inside main:
julia> outvar = 5
5
julia> invar = 5
5
julia> while true
global outvar
invar = outvar
outvar += 1
if outvar > 10
break
end
end
julia> outvar
11
julia> invar
5
So I defined both outvar and invar outside of the while loop, accessed the outvar variable outside the scope while by calling global outvar so the loop works and it does update outvar. But our invar variable is still set to 5, as the variable invar inside the while loop is not connected to the outside the while loop - it lives in its own tiny universe.
An easy way to fix this is to create a function:
function add_nums(outvar)
invar = outvar
while true
invar = outvar
outvar += 1
if outvar > 10
break
end
end
return invar
end
This takes an outvar, defines invar outside the while loop so that you can add additional logic here if you wanted to and the executes the loop and returns your new invar.
Once you have this function you can achieve the goal of the original while loop easily:
julia> outvar = 5
5
julia> invar = add_nums(outvar)
10
Even better, your outvar variable is affected by these function calls:
julia> outvar
5
I hope the above example helps you achieve what you want. You just need to create a function that implements your file loading logic.