alias template parameters - opCall caller! example breaks in Programming in D, page 530

[Brother Bill]

On page 530 of Programming in D, we have this code snippet:
```
  class C {
  void opCall() {
  writeln("C.opCall called.");
  }
  }
  // ...
  auto o = new C();
  caller!o();
  caller!({ writeln("Function literal called."); })();
```

Converted this to source/app.d
```
import std.stdio;

void main() {
	auto o = new C();
	caller!o();

	caller!({ writeln("Function literal called."); })();
}

class C {
	void opCall() {
		writeln("C.opCall called.");
	}
}

```

Compiled with DMD yielding error messages:
```
c:\dev\D\71 - 
80\c78_3k_alias_template_opCall_overload\source\app.d(5): Error: 
template instance `caller!o` template `caller` is not defined
     caller!o();
     ^
c:\dev\D\71 - 
80\c78_3k_alias_template_opCall_overload\source\app.d(7): Error: 
template instance `caller!(()
{
writeln("Function literal called.");
}
)` template `caller` is not defined
     caller!({ writeln("Function literal called."); })();
     ^
```

What is needed to get this code to compile?
My only idea is that a #import statement is missing.