Nested function introduces a variable scoping bug

[Sisyphuss]

This is a bug related to the discussion in [https://groups.google.com/forum/?fromgroups=#!topic/julia-users/ddsrBhXFJsc]:

I modified the code and tested it (v0.3.6):
Normal code:

for i = 1:2
    if i == 1
        z = "z is defined" 
        println("Iteration $i: $z") 
    elseif i == 2
        try
            println("Iteration $i: $z")
        catch
            println("Iteration $i: z is undefined")
        end 
    end
end 

Iteration 1: z is defined
Iteration 2: z is defined

Now I define a function g() inside and get a bug:

for i = 1:2
    g() = z
    if i == 1
        z = "z is defined"  
        println("Iteration $i: $z") 
    elseif i == 2
        try
            println("Iteration $i: $z")
        catch
            println("Iteration $i: z is undefined")
        end 
    end
end 

Iteration 1: z is defined
Iteration 2: z is undefined

[pao: syntax highlighting]

[JeffBezanson]

Arguably the second behavior is the correct one, and the first one is the bug. Variables only used within a loop are supposed to be newly allocated on each iteration.

[Sisyphuss]

Variables only used within a loop are supposed to be newly allocated on each iteration.

This remark is inaccurate. I rewrite the above examples with while loop:

i = 1
while i <= 2
    if i == 1
        z = "z is defined" 
        println("Iteration $i: $z") 
    elseif i == 2
        try
            println("Iteration $i: $z")
        catch
            println("Iteration $i: z is undefined")
        end 
    end
    i += 1
end 

Iteration 1: z is defined
Iteration 2: z is defined

i = 1
while i <= 2
    g() = z
    if i == 1
        z = "z is defined" 
        println("Iteration $i: $z") 
    elseif i == 2
        try
            println("Iteration $i: $z")
        catch
            println("Iteration $i: z is undefined")
        end 
    end
    i += 1
end 

Iteration 1: z is defined
Iteration 2: z is defined

Now in the second example, z is still defined.

[JeffBezanson]

Turns out this issue was described in this comment: #1571 (comment)

[JeffBezanson]

Also, I should have said "for loop" instead of "loop". for loops create a new scope on each iteration; while loops do not. The idea is that while is more of an imperative construct, and for is "parallel".

[johnmyleswhite]

Are there performance implications to having while create a new scope on each iteration? It seems to me that making while and for as similar as possible would be desirable, all else being equal.