收到错误：undefined：rego。尝试读取 rego 文件时的 ReadFile

问：

当我尝试编译代码时，出现以下错误。我已经导入了“github.com/open-policy-agent/opa/rego”，但仍然出现错误。

-bash-4.2$ go build main.go 
# command-line-arguments
./main.go:20:26: undefined: rego.ReadFile

文件名： discount_policy.rego

package discounts

rule "Bronze Discount"
    salience 10
    when
        Customer loyaltyLevel == "Bronze"
    then
        Discount.percent = 5;
        Discount.message = "You have earned a 5% discount!";
end

rule "Default Discount"
    salience 0
    then
        Discount.percent = 0;
        Discount.message = "Sorry, no discount available.";
end

文件名： main.go

package main

import (
        "context"
        "fmt"

        "github.com/open-policy-agent/opa/rego"
)

type Customer struct {
        LoyaltyLevel string `json:"loyaltyLevel"`
}

type Discount struct {
        Percent int    `json:"percent"`
        Message string `json:"message"`
}

func LoadPolicy() (*rego.Rego, error) {
        regoPolicy, err := rego.ReadFile("discount_policy.rego")
        if err != nil {
                return nil, fmt.Errorf("failed to load policy file: %w", err)
        }

        return rego.New(
                rego.Query("data.discounts.Discount"),
                rego.Compiler(regoPolicy),
        ), nil
}        

func main() {
        // Load the GRules policy
        r, err := LoadPolicy()
        if err != nil {
                fmt.Println("Policy loading error:", err)
                return
        }
}

注意：我只复制了此错误所需的代码，因为文件的代码很长。如果需要，我可以共享其余代码。我是 Go 编程的新手。

-bash-4.2$ uname -a
Linux dev-rh72-tas-1.in.intinfra.com 3.10.0-327.el7.x86_64 #1 SMP Thu Oct 29 17:29:29 EDT 2015 x86_64 x86_64 x86_64 GNU/Linux