Nested function declarations

[Andrej Mitrovic]

Well, you might be linking to an external function /and/ don't want
the function to be visible at module scope:

void main() {
   extern(C) double func();  // linked from some C library..
   double result = func();
}

You don't have to worry too much about your first example, it might
compile but it won't link:

import std.math: sqrt;
void main() {
   double sqrt();
   double result = sqrt();
}

 Error 42: Symbol Undefined _D12externalTest4mainFZv4sqrtMFZd
--- errorlevel 1