DLL, export bool dfunc(char[] s, extern (Windows) bool function() cb)

[Bjoern]

Subject; DLL function calls callback function in callee (parent)

like
// MyDLL a Dll written in D
export bool dfunc(char[] s,extern (Windows)char[] function() cb)
{
    while ( char[] t = tokenize(s)) cb(t);
    return true;
}

I have to use some 4GL code to explain:


FUNCTION GetResult(StringToAnanlyse is string = "Hello from 4GL")
// Call dfunc , pass StringToAnalyse, and address of CallBack Function
   IF API("MyDLL", "dfunc", StringToAnanlyse, &ReceiveResult)
   END

// The CallBack Function
PRIVATE FUNCTION ReceiveResult(token is string)
   WHILE token <> ""
     Trace(token)
     newString += (token + ",") // defined elsewhere
   END
   RESULT newString
// Output
Hello
from
4GL
newString == "Hello,from,4GL,"
---------------------------------------------------
I ask here instead of D.lean because I mean the official "DLLs in D" 
documents should explain this functionality too.

Oh, the question :)

export bool dfunc(char[] s, extern (Windows) char[] function() cb)

I think at least my intention is clear , so I hope somebody is willing 
to  show me how to implement such a DLL function.

Many thanks in advance, Bjoern