Proposal of a general do-while loop

[Charles D Hixson]

Taro Kawagishi wrote:
> Hello all,
> 
> every once in a while I feel uneasy when I find I can't fit my logic into a do-while or while loop in a concise way.
> Here is a C++ example:
> 
> void
> find_string_occurrences(const string& text, const string& pattern) {
> 
>     // listing 1
>     size_t pos = text.find(pattern, 0);
>     while (pos != string::npos) {
>         cout << "pattern found at " << pos << "\n";
>         ++pos;
>         pos = text.find(pattern, pos);
>     }
> 
> }
> ...
to me the best solution would appear something along the lines of:
    loop
    {  size_t pos = text.find(pattern, 0);
       // declare a new pos on each iteration??
       if (pos == string::npos)  break;
       cout << "pattern found at " << pos << "\n";
       // tango is not standard D, but I think I understand
       // what you are doing
       ++pos;
       pos = text.find(pattern, pos);
    }

I'd prefer the Ada-esque
      exit when (pos == string::npos);
but that means introducing new key words (more than just 
"loop").  OTOH, I guess there's nothing wrong with having an 
un-parameterized "do" instead of loop, as in:
    do
    {  ... do stuff ...
       when(condition) break;
    }
in the case the "when" is semantically the same as an if, but 
it clarifies what's going on.  One could limit it's use to 
"only usable within a do loop".  But I would prefer the syntax 
of either:
       exit when (condition);
or
       break when (condition);
as I feel that these are clearer.