[julia-users] Accessing the loop variable (and pi as float)

[Hans W Borchers]

Yesterday I implemented a function calculating arc length of curves (to the 
last digit) when I came across the following stumbling blocks. Image the 
following function where I leave a for-loop with a 'break' statement:

    function testfun1(x::Vector{Float64})
        for i = 1:length(x)
            if x[i] == 0.0
                break
            end
        end
        return i-1
    end

    julia> testfun([1.0, 2.0, 3.0, 0.0, 1.0])
    ERROR: i not defined
     in testfun at none:7

I understand that the scope of the loop variable is restricted to the loop 
itself. What is the best way to "export"  i  to the outside? For the moment 
I settled with defining i before the loop.

    function testfun2(x::Vector{Float64})
        local i::Int
        for i = 1:length(x)
            if x[i] == 0.0
                break
            end
        end
        return i-1
    end

This works, but I must admit it runs against my gut feeling and experience 
with other scientific programming languages.


The next shock was the following:

    function testfun(x::Float64)
    return x^2
    end

    julia> testfun(pi)
    ERROR: no method testfun(MathConst{:π})

Again, I learned that I can use testfun(float(pi) , but my feeling would be 
that pi should be converted to float automatically whenever the context 
requires it. On the mailing list I think I have seen other complaints about 
this. I would prefer that  pi  and MathConst{:π} (or even better π alone) 
were different objects.