Proposal of a general do-while loop

[janderson]

downs wrote:
> Taro Kawagishi wrote:
>> I think a more natural way to express the logic is to write the code 
>> as in listing 4.
>>
>>     // listing 4
>>     size_t pos = 0;
>>     do {
>>         pos = text.find(pattern, pos);
>>     } while (pos != string::npos) {
>>         cout << "pattern found at " << pos << "\n";
>>         ++pos;
>>     }
>>
>> The meaning of
>>
>>     do {
>>         aa;
>>     } while (bb) {
>>         cc;
>>     }
>>
>> is
>>
>>     while (true) {
>>         aa;
>>         if (not bb) {
>>             break;
>>         }
>>         cc;
>>     }
> 
> void doWhile(void delegate() pre, lazy bool cond, void delegate() post) {
>   while (true) {
>     pre;
>     if (!cond()) break;
>     post;
>   }
> }
> 
> // listing 4, modified
> size_t pos=0;
> doWhile ({
>   pos=text.find(pattern, pos);
> }, pos!=string::npos, {
>   writefln("Pattern found at ", pos);
>   ++pos;
> });
> 
> Not tested, but should work.
> Have fun!

Nice.  Not that I really think we need this new construct however this 
is what I was thinking. (untested)


struct WhileStruct
{
	void delegate() pre;
	bool delegate() cond;
	void opCall(void delegate() post)
	{	
		while (true)
		{	
			pre();
			if (!cond()) break;
			post();
		}
	}
}

struct Do
{

	void delegate() pre;
	static Do opCall(void delegate() pre) //could be a free function
	{
		Do d;
		d.pre = pre;
		return d;
	}

	WhileStruct While(lazy bool cond)
	{
		WhileStruct w;
		w.pre = pre;
		w.cond = {return cond();};
		return w;
	}

}

void main()
{
//	Do({...}).  //Note that "dot" is the nastiest part
//	While(...)({...});

//ie
	Do({pos=text.find(pattern, pos);}).
	While(pos != string::npos)
	({
		writefln("Pattern found at ", pos);
		++pos;
	});
	
}


Here are some other forms I think would be possible to code in a library 
in D.

Do({...})(...)({...});
Do[{...}]()[{...}];

Do({...})
(While(...))({...});


while (Do(..., {...}))
{

};

Do({...}) = While(...)
({});

Do({...}) = (...) = ({});
Do({...}) ~ (...) ~ ({});

Do({...});    //Essentially stores a delegate on the stack
While(...)
({...});

The power of D.