D: How to check if a function is chained? a().b().c();

[BoQsc via Digitalmars-d-learn]

Let's say we have a chain of functions.
```
 a().b().c();
```

I would like to have a behaviour in `a()` that would check if 
there is `b()` or `c()` chained to it.

If `a();`is not chained: do a `writeln("You forgot to chain this 
function!");`

#### A function that executes a program

For me syntactically it is important. One real world application 
would be:

`program("someProgramName").pipe("someOtherProgramName");`
Executes and pipes output to another program.

`program();` - Only executes the program.