Writing a mutable function (exclamation mark function)

[dwo...@gmail.com]

I'm currently trying to understand how functions with an exclamation mark at the end work. I know the exclamation mark is just a notational point however I'm currently confused at how to actually write a mutable function.

If a = 1

function add_one(a)

    return a + 1

end

running add_one(a) twice outputs:

    2

    2

how would I create add_one!(a) to output:

    2

    3

[John Myles White]

http://julia.readthedocs.org/en/release-0.3/manual/faq/#i-passed-an-argument-x-to-a-function-modified-it-inside-that-function-but-on-the-outside-the-variable-x-is-still-unchanged-why

http://www.johnmyleswhite.com/notebook/2014/09/06/values-vs-bindings-the-map-is-not-the-territory/

[andrew cooke]

does this help any?

julia> a = 1
1

julia> function inc()
        a = a+1
       end
inc (generic function with 1 method)

julia> inc()
ERROR: UndefVarError: a not defined
 in inc at none:2

julia> function inc()
        global a = a+1
       end
inc (generic function with 1 method)

julia> inc()
2

julia> inc()
3

julia> inc()
4

julia> inc()
5

julia> function make_inc(start)
        a = start
        function inc()
         a = a + 1
        end
       end
make_inc (generic function with 1 method)

julia> inc2 = make_inc(99)
inc (generic function with 1 method)

julia> inc2()
100

julia> inc2()
101

julia> inc2()
102

also http://julia.readthedocs.org/en/latest/manual/variables-and-scoping/

andrew