mkdir -p $GOPATH/src/golang.org/x
cd $GOPATH/src/golang.org/x
git clone https://github.com/golang/tools.git
cd tools/cmd/godoc
go install 
ls -alh $GOPATH/bin

linux@ubuntu:/usr/local/go/src/log$ go doc
package log // import "log"
 
Package log implements a simple logging package. It defines a type, Logger,
with methods for formatting output. It also has a predefined 'standard'
Logger accessible through helper functions Print[f|ln], Fatal[f|ln], and
Panic[f|ln], which are easier to use than creating a Logger manually. That
logger writes to standard error and prints the date and time of each logged
message. Every log message is output on a separate line: if the message
being printed does not end in a newline, the logger will add one. The Fatal
functions call os.Exit(1) after writing the log message. The Panic functions
call panic after writing the log message.
 
const Ldate = 1  iota ...
func Fatal(v ...interface{})
func Fatalf(format string, v ...interface{})
func Fatalln(v ...interface{})
func Flags() int
func Output(calldepth int, s string) error
func Panic(v ...interface{})
func Panicf(format string, v ...interface{})
func Panicln(v ...interface{})
func Prefix() string
func Print(v ...interface{})
func Printf(format string, v ...interface{})
func Println(v ...interface{})
func SetFlags(flag int)
func SetOutput(w io.Writer)
func SetPrefix(prefix string)
type Logger struct{ ... }
 func New(out io.Writer, prefix string, flag int) *Logger

linux@ubuntu:/usr/local/go/src/log$ go doc log.Fatal
func Fatal(v ...interface{})
 Fatal is equivalent to Print() followed by a call to os.Exit(1).

linux@ubuntu:/usr/local/go/src/log$ go doc Logger
type Logger struct {
  // Has unexported fields.
}
 A Logger represents an active logging object that generates lines of output
 to an io.Writer. Each logging operation makes a single call to the Writer's
 Write method. A Logger can be used simultaneously from multiple goroutines;
 it guarantees to serialize access to the Writer.
func New(out io.Writer, prefix string, flag int) *Logger
func (l *Logger) Fatal(v ...interface{})
func (l *Logger) Fatalf(format string, v ...interface{})
func (l *Logger) Fatalln(v ...interface{})
func (l *Logger) Flags() int
func (l *Logger) Output(calldepth int, s string) error
func (l *Logger) Panic(v ...interface{})
func (l *Logger) Panicf(format string, v ...interface{})
func (l *Logger) Panicln(v ...interface{})
func (l *Logger) Prefix() string
func (l *Logger) Print(v ...interface{})
func (l *Logger) Printf(format string, v ...interface{})
func (l *Logger) Println(v ...interface{})
func (l *Logger) SetFlags(flag int)
func (l *Logger) SetOutput(w io.Writer)
func (l *Logger) SetPrefix(prefix string)

/*
簡易計算器計算自定義包
 */
package documents
 
// 一種實現兩個整數相加的函數，
// 返回值為兩整數相加之和
func Add(a, b int) int {
 return a + b
}
 
// 一種實現兩個整數相減的函數，
// 返回值為兩整數相減之差
func Sub(a, b int) int {
 return a - b
}
 
// 一種實現兩個整數相乘的函數，
// 返回值為兩整數相乘之積
func Mul(a, b int) int {
 return a * b
}
 
// 一種實現兩個整數相除的函數，
// 返回值為兩整數相除之商
func Div(a, b int) int {
 if b == 0 {
  panic("divide by zero")
 } 
 return a / b
}

package documents 
import (
 "fmt"
)
 
func ExampleAdd() {
 result := Add(4, 2)
 fmt.Println("4 + 2 =", result)
 
 // Output:
 // 4 + 2 = 6
}
 
func ExampleSub() {
 result := Sub(4, 2)
 fmt.Println("4 - 2 =", result)
 
 // Output:
 // 4 - 2 = 2
}
 
func ExampleMul() {
 result := Mul(4, 2)
 fmt.Println("4 * 2 =", result)
 
 // Output:
 // 4 * 2 = 8
}
 
func ExampleDiv() {
 result := Div(4,2)
 fmt.Println("4 / 2 =", result)
 
 // Output:
 // 4 / 2 = 2
}