}
			// x is a constant so xval != nil and it must be of Int kind.
			x.val = constant.Shift(xval, op, uint(s))
			x.expr = e
			opPos := x.Pos()
			if b, _ := e.(*ast.BinaryExpr); b != nil {
				opPos = b.OpPos
			}
			check.overflow(x, opPos)
			return
		}

		// non-constant shift with constant lhs
		if isUntyped(x.typ) {
			// spec: "If the left operand of a non-constant shift

			return false
		}
	} else {
		check.errorf(x, InvalidSyntaxTree, "unknown operator %s", op)
		return false
	}
	return true
}

// opPos returns the position of the operator if x is an operation;
// otherwise it returns the start position of x.
func opPos(x syntax.Expr) syntax.Pos {
	switch op := x.(type) {
	case nil:
		return nopos // don't crash
	case *syntax.Operation:
		return op.Pos()
	default:

	for p.tok == token.OR {
		t := new(ast.BinaryExpr)
		t.OpPos = p.pos
		t.Op = token.OR
		p.next()
		t.X = x
		t.Y = p.embeddedTerm()
		x = t
	}
	return x
}

func (p *parser) embeddedTerm() ast.Expr {
	if p.trace {
		defer un(trace(p, "EmbeddedTerm"))
	}
	if p.tok == token.TILDE {
		t := new(ast.UnaryExpr)
		t.OpPos = p.pos
		t.Op = token.TILDE
		p.next()

	p.expr1(x.X, prec, depth+diffPrec(x.X, prec))
	if printBlank {
		p.print(blank)
	}
	xline := p.pos.Line // before the operator (it may be on the next line!)
	yline := p.lineFor(x.Y.Pos())
	p.setPos(x.OpPos)
	p.print(x.Op)
	if xline != yline && xline > 0 && yline > 0 {
		// at least one line break, but respect an extra empty line
		// in the source
		if p.linebreak(yline, 1, ws, true) > 0 {
			ws = ignore