// 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{

	// 		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 {