// ----------------------------------------------------------------------------
// Expressions

func walkBinary(e *ast.BinaryExpr) (has4, has5 bool, maxProblem int) {
	switch e.Op.Precedence() {
	case 4:
		has4 = true
	case 5:
		has5 = true
	}

	switch l := e.X.(type) {
	case *ast.BinaryExpr:
		if l.Op.Precedence() < e.Op.Precedence() {
			// parens will be inserted.

// Expressions

func (p *parser) expr() Expr {
	if trace {
		defer p.trace("expr")()
	}

	return p.binaryExpr(nil, 0)
}

// Expression = UnaryExpr | Expression binary_op Expression .
func (p *parser) binaryExpr(x Expr, prec int) Expr {
	// don't trace binaryExpr - only leads to overly nested trace output

	if x == nil {
		x = p.unaryExpr()
	}

	return true
}

// opName returns the name of the operation if x is an operation
// that might overflow; otherwise it returns the empty string.
func opName(e ast.Expr) string {
	switch e := e.(type) {
	case *ast.BinaryExpr:
		if int(e.Op) < len(op2str2) {
			return op2str2[e.Op]
		}
	case *ast.UnaryExpr:
		if int(e.Op) < len(op2str1) {
			return op2str1[e.Op]
		}
	}
	return ""
}

var op2str1 = [...]string{

func (p *parser) embeddedElem(x ast.Expr) ast.Expr {
	if p.trace {
		defer un(trace(p, "EmbeddedElem"))
	}
	if x == nil {
		x = p.embeddedTerm()
	}
	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 {

	if p.trace {
		defer un(trace(p, "BinaryExpr"))
	}

	x := p.parseUnaryExpr(lhs)
	for prec := p.tok.Precedence(); prec >= prec1; prec-- {
		for p.tok.Precedence() == prec {
			pos, op := p.pos, p.tok
			p.next()
			if lhs {
				p.resolve(x)
				lhs = false
			}
			y := p.parseBinaryExpr(false, prec+1)
			x = &ast.BinaryExpr{p.checkExpr(x), pos, op, p.checkExpr(y)}
		}
	}

	// 		goto Error
	// 	}
	// 	if e.Op == token.ARROW {
	// 		x.expr = e
	// 		return statement // receive operations may appear in statement context
	// 	}

	// case *syntax.BinaryExpr:
	// 	check.binary(x, e, e.X, e.Y, e.Op)
	// 	if x.mode == invalid {
	// 		goto Error
	// 	}

	case *syntax.Operation:
		if e.Y == nil {
			// unary expression
			if e.Op == syntax.Mul {