[julia-users] Is there a performance penalty for defining functions inside functions?

[Evan Fields]

To keep namespaces clear and to help with code readability, I might like to 
do this:

function mainFunc()
    function helper()
        do stuff
        return something
    end

    call helper() and do stuff
    return something
end

That way the helper function is only visible to the function that needs it 
and when reading the code it's obvious that the helper "belongs to" the 
main function. Is there any performance penalty for doing this? Or is this 
bad practice for some reason I don't know?