《Go语言编程》calc.go的错误

最近看由人民邮电出版社许式伟 吕桂华等编著《Go语言编程》【第1章初识Go语言】【1.5 工程管理】时，发现了示例代码calc.go有几处错误，args := os.Args数组变量args[0]代表程序自身，3个if语句len(args)条件判断右值也都小了1，按照书本编写代码运行时将会一直执行匿名函数Usage(),显示如下：

USAGE: calc command [arguments] ...

The commands are:

add     Addition of two values.

sqrt    Square root of a non-negative value.

正确的calc.go代码如下：

// calc.go
package main

import (
    "fmt"
    "os"
    "simplemath"
    "strconv"
)

var Usage = func() {
    fmt.Println("USAGE: calc command [arguments] ...")
    fmt.Println("\nThe commands are:\n\tadd\tAddition of two values.\n\tsqrt\tSquare root of a non-negative value.")
}

func main() {
    args := os.Args
    if args == nil || len(args) < 3 {
        Usage()
        return
    }

switch args[1] {
    case "add":
        if len(args) != 4 {
            fmt.Println("USAGE: calc add <integer1><integer2>")
            return
        }
        v1, err1 := strconv.Atoi(args[2])
        v2, err2 := strconv.Atoi(args[3])
        if err1 != nil || err2 != nil {
            fmt.Println("USAGE: calc add <integer1><integer2>")
            return
        }
        ret := simplemath.Add(v1, v2)
        fmt.Println("Result: ", ret)
    case "sqrt":
        if len(args) != 3 {
            fmt.Println("USAGE: cale sqrt <integer>")
            return
        }
        v, err := strconv.Atoi(args[2])
        if err != nil {
            fmt.Println("USAGE: calc sqrt <integer>")
            return
        }
        ret := simplemath.Sqrt(v)
        fmt.Println("Result: ", ret)
    default:
        Usage()
    }
}