//	                  ::= <substitution>
//
//	<decltype> ::= Dt <expression> E
//	           ::= DT <expression> E
func (st *state) prefix() AST {
	var a AST

	// The last name seen, for a constructor/destructor.
	var last AST

	var module AST

	getLast := func(a AST) AST {
		for {
			if t, ok := a.(*Template); ok {
				a = t.Name
			} else if q, ok := a.(*Qualified); ok {
				a = q.Name