Null references redux

[Nick Sabalausky]

"language_fan" <foo at bar.com.invalid> wrote in message 
news:h9relp$1ebg$4 at digitalmars.com...
> Mon, 28 Sep 2009 22:33:26 +0000, language_fan thusly wrote:
>
>> Value types can be incorrectly initialized and nobody notices. E.g.
>>
>>   int min;
>>
>>   foreach(int value; list)
>>     if (value < min) min = value;
>
>> Now I can tell you, in functional languages there is no other way. All
>> initializations have to be correct, they are final, they are constants
>> and they can be initialized incorrectly. But there are some tools that
>> help in this. Functions can be automatically tested. Invariants, pre-
>> and post-conditions can be set. Still, I can even bet they are much
>> safer than D in every possible way. How is this possible?
>
> For instance if I use the example given above, I write it like this in a
> functional language:
>
> find_min:: Ord a => [a] -> Maybe a
> find_min [] = Nothing
> find_min (h:t) = Just $ foldl min h t
>
> You can then use quickcheck to verify the result in some fancy way.
>
> I just cannot think of any way how you could crash programs written in
> this way. They are solid as a rock.

I'm not particulary accustomed to that sort of syntax. Am I correct in my 
analysis that that essentially does something like this?:

// Assuming that:
// 1. Variables of type void could be declared and had value 'void'.
// 2. 'any(T,U,V)' was a "supertype" that can and must be one (and only one) 
of T, U, or V.

immutable any(int,void) min(immutable any(int,void) a, immutable 
any(int,void) b)
{
    static if( is(typeof(a) == void) && is(typeof(b) == void) )
        return void;
    else static if( is(typeof(a) == int) && is(typeof(b) == void) )
        return a;
    else static if( is(typeof(a) == void) && is(typeof(b) == int) )
        return b;
    else
        return a<b? a : b;
}

immutable any(int,void) findMin(immutable int[] list)
{
    static if(list.length == 0)
        return void;
    else
        return reduce!("min(a,b)")(list); // 'reduce' from phobos2
}