Re: Local and Global Variables

[Coda Highland <chighland@...>]

On Fri, Apr 26, 2013 at 8:48 AM, Doug Currie <doug.currie@gmail.com> wrote:
>
> On Apr 26, 2013, at 7:13 AM, Thomas Jericke <tjericke@indel.ch> wrote:
>
>> To me there are still some problems regarding scoping with this, consider:
>>
>> if someboolean then
>>    global myvar = 0
>> end
>>
>> print(myvar) -- Is this valid?
>>
>> Probably the most consistent way would be, that scoping is used for globals too and you would have to do this:
>>
>> global myvar
>>
>> if someboolean then
>>    myvar = 0
>>    global g2
>> end
>>
>> print(myvar) -- ok
>> g2 = 0 -- error
>
> If this is what you want, then the local and global keywords mean the same thing. In expression oriented languages of the ML family, this keyword is called val. It declares a new value in the present scope. So your example becomes:
>
> val myvar
>
> if someboolean then
>    myvar = 0
>    val g2 = 7
> end
>
> I like this approach, but I am not advocating a change to Lua.
>
> This can also be accomplished with a new operator. In mathematics, := is often used for definitions.
>
> myvar := nil -- global declaration and initialization
>
> if someboolean then
>    myvar = 0 -- assignment
>    g2 := 7   -- local declaration and initialization
> end
>
> I am not advocating this either, but it may spark some derivative language experiments.
>
> e
>
>

No, they don't quite mean the same thing. They mean the same thing in
terms of the scope of the *name*, but not the scope of the *value*.
Multiple "local x" statements each create a new local variable named
x, while multiple "global x" statements would all refer to the same
global variable named x.

Consider:

global x = 3

function foo(y)
    print(x) -- error
    if y > 5 then
        global x = 6
        print(x) -- legal
    end
    print(x) -- error
end

print(x) -- legal, outputs 3
foo(8) -- legal assuming you take out the print statements
print(x) -- legal, outputs 8

/s/ Adam