Re: Globals vs. Locals

[David Given <dg@...>]

On Friday 05 August 2005 21:21, Vijay Aswadhati wrote:
[...]
> C# provides an overloaded feature using the 'using' [1] keyword that is
> pretty nice - sugar-wise; with some adaptation a feature like that provides
> a nice balance and can solve to a certain degree the global versus local
> debate.

C++ has 'using', too, and like a lot of things C++ does, gets it wrong... (you 
can't import a symbol from one namespace into another *and give it a 
different name*. You can create an alias for a type in a different namespace 
with typedef, but if your symbol isn't a type you're doomed.)

[...]
> using ( table, string, ... )
> do

The issue with this is that Lua doesn't really have locals vs. globals. It has 
locals defined in this scope vs. locals defined in an outer scope vs. locals 
defined in the scope outside that, etc.

(Strictly, Lua's globals aren't variables --- all that happens is that if the 
parser sees a symbol it doesn't recognise, it converts it into a lookup of 
the globals table. They're quite different things to real variables, defined 
with the 'local' keyword.)

So with your suggestion, I can see two main problems: the minor one is that I 
can't say *where* I want to import the symbols, but the major one is that 
it's loads of typing. Say we've got this:

local init = function (object, param1, param2, param3, param4, param5, param6)
	local createobject = function ()
		return param1 + param2 + param3 + param4 + param5 + param6
	end

	object.t1 = createobject()
	object.t2 = createobject()
	...etc...
end

With explicit importing from an outer scope into an inner scope, I have to 
declare my parameter list twice. It's loads more typing and makes me rather 
less inclined to use this feature.

(C++ is even worse. Trying to declare a nested function in C++ involves having 
to create an inner class with a static method containing your function... and 
C++ doesn't have nested scopes, so you have to explicitly pass all your 
parameters into the nested function! The pain! The typing!)

(Forth is way better. Creating a Forth function is four characters, plus the 
name. They say that a good Forth function can be expressed clearly in one 
line of code. This encourages fine-grained factoring and code reuse, and goes 
a long way to explain how Forth code tends to be about half the size of the 
equivalent C.)

(Actually, I'd love a minimum-typing lambda expression syntax in Lua. I'd very 
much like to be able to say something like [ return 4 ] and have it turn into 
a nested function; there's a lot of cool stuff you can do with syntax like 
this, such as defining your own control-flow routines. See Smalltalk, which 
has *no* control-flow syntax in the language. It uses closures for 
everything.)

[...]
> -- somewhere else, foo could be invoked like this:
> foo (a1, a2, a3) using (table, string)
[...]
> I wonder if something like this could be achieved using LHF's proposed
> preprocessor and the setenv/getenv functions.

...or I could be misunderstanding you entirely. Are you talking about lexical 
scoping or run-time scoping?

-- 
"Curses! Foiled by the chilled dairy treats of righteousness!" --- Earthworm 
Jim (evil)

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