func (s *Slice) Line() int {
	return s.line
}

func (s *Slice) Col() int {
	// TODO: Col is only called when defining a macro and all it cares about is increasing
	// position to discover whether there is a blank before the parenthesis.
	// We only get here if defining a macro inside a macro.
	// This imperfect implementation means we cannot tell the difference between
	//	#define A #define B(x) x
	// and
	//	#define A #define B (x) x

You only give `Depends` a single parameter.

This parameter must be something like a function.

You **don't call it** directly (don't add the parenthesis at the end), you just pass it as a parameter to `Depends()`.

And that function takes parameters in the same way that *path operation functions* do.

/// tip