p.expect(token.LPAREN)
	var typ ast.Expr
	if p.tok == token.TYPE {
		// type switch: typ == nil
		p.next()
	} else {
		typ = p.parseType()
	}
	p.expect(token.RPAREN)

	return &ast.TypeAssertExpr{x, typ}
}

func (p *parser) parseIndexOrSlice(x ast.Expr) ast.Expr {
	if p.trace {
		defer un(trace(p, "IndexOrSlice"))
	}

	lbrack := p.expect(token.LBRACK)
	p.exprLev++

		stmt := stmt.(*ir.AssignListStmt)
		r := rhs[0]

		switch r.Op() {
		case ir.OINDEXMAP:
			stmt.SetOp(ir.OAS2MAPR)
		case ir.ORECV:
			stmt.SetOp(ir.OAS2RECV)
		case ir.ODOTTYPE:
			r := r.(*ir.TypeAssertExpr)
			stmt.SetOp(ir.OAS2DOTTYPE)
			r.SetOp(ir.ODOTTYPE2)
		case ir.ODYNAMICDOTTYPE:
			r := r.(*ir.DynamicTypeAssertExpr)
			stmt.SetOp(ir.OAS2DOTTYPE)
			r.SetOp(ir.ODYNAMICDOTTYPE2)
		default:

			}
			typeof[n] = join(out)
			for i, arg := range n.Args {
				if i >= len(in) {
					break
				}
				if typeof[arg] == "" {
					typeof[arg] = in[i]
				}
			}

		case *ast.TypeAssertExpr:
			// x.(type) has type of x.
			if n.Type == nil {
				typeof[n] = typeof[n.X]
				return
			}
			// x.(T) has type T.
			if t := typeof[n.Type]; isType(t) {
				typeof[n] = getType(t)

	case ir.OAS2DOTTYPE, ir.OAS2RECV, ir.OAS2MAPR:
		n := n.(*ir.AssignListStmt)
		t := o.markTemp()
		o.exprList(n.Lhs)

		switch r := n.Rhs[0]; r.Op() {
		case ir.ODOTTYPE2:
			r := r.(*ir.TypeAssertExpr)
			r.X = o.expr(r.X, nil)
		case ir.ODYNAMICDOTTYPE2:
			r := r.(*ir.DynamicTypeAssertExpr)
			r.X = o.expr(r.X, nil)
			r.RType = o.expr(r.RType, nil)
			r.ITab = o.expr(r.ITab, nil)
		case ir.ORECV:

		return // nothing to do
	}

	// update operands of x if necessary
	switch x := x.(type) {
	case *ast.BadExpr,
		*ast.FuncLit,
		*ast.CompositeLit,
		*ast.IndexExpr,
		*ast.SliceExpr,
		*ast.TypeAssertExpr,
		*ast.StarExpr,
		*ast.KeyValueExpr,
		*ast.ArrayType,
		*ast.StructType,
		*ast.FuncType,
		*ast.InterfaceType,
		*ast.MapType,
		*ast.ChanType:

		n.SetOp(ir.OMETHVALUE)
		n.SetType(NewMethodType(n.Type(), nil))
	}
	return n
}

// tcDotType typechecks an ODOTTYPE node.
func tcDotType(n *ir.TypeAssertExpr) ir.Node {
	n.X = Expr(n.X)
	n.X = DefaultLit(n.X, nil)
	l := n.X
	t := l.Type()
	if t == nil {
		n.SetType(nil)
		return n
	}
	if !t.IsInterface() {

		n := n.(*SelectorExpr)
		exprFmt(n.X, s, nprec)
		if n.Sel == nil {
			fmt.Fprint(s, ".<nil>")
			return
		}
		fmt.Fprintf(s, ".%s", n.Sel.Name)

	case ODOTTYPE, ODOTTYPE2:
		n := n.(*TypeAssertExpr)
		exprFmt(n.X, s, nprec)
		fmt.Fprintf(s, ".(%v)", n.Type())

	case OINDEX, OINDEXMAP:
		n := n.(*IndexExpr)
		exprFmt(n.X, s, nprec)
		fmt.Fprintf(s, "[%v]", n.Index)

		default:
			check.error(s, InvalidSyntaxTree, "incorrect form of type switch guard")
			return
		}

		// rhs must be of the form: expr.(type) and expr must be an ordinary interface
		expr, _ := rhs.(*ast.TypeAssertExpr)
		if expr == nil || expr.Type != nil {
			check.error(s, InvalidSyntaxTree, "incorrect form of type switch guard")
			return
		}
		var x operand
		check.expr(nil, &x, expr.X)
		if x.mode == invalid {

	// exprs
	case ir.OCOMPLIT:
		return tcCompLit(n.(*ir.CompLitExpr))

	case ir.OXDOT, ir.ODOT:
		n := n.(*ir.SelectorExpr)
		return tcDot(n, top)

	case ir.ODOTTYPE:
		n := n.(*ir.TypeAssertExpr)
		return tcDotType(n)

	case ir.OINDEX:
		n := n.(*ir.IndexExpr)
		return tcIndex(n)

	case ir.ORECV:
		n := n.(*ir.UnaryExpr)
		return tcRecv(n)

	case ir.OSEND:

	var typ ast.Expr
	if p.tok == token.TYPE {
		// type switch: typ == nil
		p.next()
	} else {
		typ = p.parseType()
	}
	rparen := p.expect(token.RPAREN)

	return &ast.TypeAssertExpr{X: x, Type: typ, Lparen: lparen, Rparen: rparen}
}

func (p *parser) parseIndexOrSliceOrInstance(x ast.Expr) ast.Expr {
	if p.trace {
		defer un(trace(p, "parseIndexOrSliceOrInstance"))
	}