x.mode = invalid
		return
	}

	x.mode = value

	// spec: "Only the first index may be omitted; it defaults to 0."
	if e.Slice3 && (e.High == nil || e.Max == nil) {
		check.error(inNode(e, e.Rbrack), InvalidSyntaxTree, "2nd and 3rd index required in 3-index slice")
		x.mode = invalid
		return
	}

	// check indices
	var ind [3]int64
	for i, expr := range []ast.Expr{e.Low, e.High, e.Max} {

	{50, "ENOCSI", "no CSI structure available"},
	{51, "EL2HLT", "level 2 halted"},
	{52, "EBADE", "invalid exchange"},
	{53, "EBADR", "invalid request descriptor"},
	{54, "EXFULL", "exchange full"},
	{55, "ENOANO", "no anode"},
	{56, "EBADRQC", "invalid request code"},
	{57, "EBADSLT", "invalid slot"},
	{59, "EBFONT", "bad font file format"},
	{60, "ENOSTR", "device not a stream"},
	{61, "ENODATA", "no data available"},

	{50, "ENOCSI", "no CSI structure available"},
	{51, "EL2HLT", "level 2 halted"},
	{52, "EBADE", "invalid exchange"},
	{53, "EBADR", "invalid request descriptor"},
	{54, "EXFULL", "exchange full"},
	{55, "ENOANO", "no anode"},
	{56, "EBADRQC", "invalid request code"},
	{57, "EBADSLT", "invalid slot"},
	{59, "EBFONT", "bad font file format"},
	{60, "ENOSTR", "device not a stream"},
	{61, "ENODATA", "no data available"},

	{50, "ENOCSI", "no CSI structure available"},
	{51, "EL2HLT", "level 2 halted"},
	{52, "EBADE", "invalid exchange"},
	{53, "EBADR", "invalid request descriptor"},
	{54, "EXFULL", "exchange full"},
	{55, "ENOANO", "no anode"},
	{56, "EBADRQC", "invalid request code"},
	{57, "EBADSLT", "invalid slot"},
	{59, "EBFONT", "bad font file format"},
	{60, "ENOSTR", "device not a stream"},
	{61, "ENODATA", "no data available"},

	{50, "ENOCSI", "no CSI structure available"},
	{51, "EL2HLT", "level 2 halted"},
	{52, "EBADE", "invalid exchange"},
	{53, "EBADR", "invalid request descriptor"},
	{54, "EXFULL", "exchange full"},
	{55, "ENOANO", "no anode"},
	{56, "EBADRQC", "invalid request code"},
	{57, "EBADSLT", "invalid slot"},
	{59, "EBFONT", "bad font file format"},
	{60, "ENOSTR", "device not a stream"},
	{61, "ENODATA", "no data available"},

	}
}

// IsEmptyTree reports whether this tree (node) is empty of everything but space or comments.
func IsEmptyTree(n Node) bool {
	switch n := n.(type) {
	case nil:
		return true
	case *ActionNode:
	case *CommentNode:
		return true
	case *IfNode:
	case *ListNode:
		for _, node := range n.Nodes {
			if !IsEmptyTree(node) {
				return false
			}
		}
		return true

	{45, "EDEADLK", "resource deadlock avoided"},
	{46, "ENOLCK", "no locks available"},
	{50, "EBADE", "invalid exchange"},
	{51, "EBADR", "invalid request descriptor"},
	{52, "EXFULL", "exchange full"},
	{53, "ENOANO", "no anode"},
	{54, "EBADRQC", "invalid request code"},
	{55, "EBADSLT", "invalid slot"},
	{56, "EDEADLOCK", "file locking deadlock error"},
	{59, "EBFONT", "bad font file format"},
	{60, "ENOSTR", "device not a stream"},

	{50, "ENOCSI", "no CSI structure available"},
	{51, "EL2HLT", "level 2 halted"},
	{52, "EBADE", "invalid exchange"},
	{53, "EBADR", "invalid request descriptor"},
	{54, "EXFULL", "exchange full"},
	{55, "ENOANO", "no anode"},
	{56, "EBADRQC", "invalid request code"},
	{57, "EBADSLT", "invalid slot"},
	{58, "EDEADLOCK", "file locking deadlock error"},
	{59, "EBFONT", "bad font file format"},
	{60, "ENOSTR", "device not a stream"},

	{45, "EDEADLK", "resource deadlock avoided"},
	{46, "ENOLCK", "no locks available"},
	{50, "EBADE", "invalid exchange"},
	{51, "EBADR", "invalid request descriptor"},
	{52, "EXFULL", "exchange full"},
	{53, "ENOANO", "no anode"},
	{54, "EBADRQC", "invalid request code"},
	{55, "EBADSLT", "invalid slot"},
	{56, "EDEADLOCK", "file locking deadlock error"},
	{59, "EBFONT", "bad font file format"},
	{60, "ENOSTR", "device not a stream"},

		default:
			check.errorf(&x, NotAType, "%s is not a type", &x)
		}

	case *ast.IndexExpr, *ast.IndexListExpr:
		ix := typeparams.UnpackIndexExpr(e)
		check.verifyVersionf(inNode(e, ix.Lbrack), go1_18, "type instantiation")
		return check.instantiatedType(ix, def)

	case *ast.ParenExpr:
		// Generic types must be instantiated before they can be used in any form.