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< ol class = "chapter" > < li class = "chapter-item expanded affix " > < a href = "../index.html" > Go语言圣经< / a > < / li > < li class = "chapter-item expanded affix " > < a href = "../preface.html" > 前言< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1.html" > < strong aria-hidden = "true" > 1.< / strong > 入门< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-01.html" > < strong aria-hidden = "true" > 1.1.< / strong > Hello, World< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-02.html" > < strong aria-hidden = "true" > 1.2.< / strong > 命令行参数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-03.html" > < strong aria-hidden = "true" > 1.3.< / strong > 查找重复的行< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-04.html" > < strong aria-hidden = "true" > 1.4.< / strong > GIF动画< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-05.html" > < strong aria-hidden = "true" > 1.5.< / strong > 获取URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-06.html" > < strong aria-hidden = "true" > 1.6.< / strong > 并发获取多个URL< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-07.html" > < strong aria-hidden = "true" > 1.7.< / strong > Web服务< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch1/ch1-08.html" > < strong aria-hidden = "true" > 1.8.< / strong > 本章要点< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2.html" > < strong aria-hidden = "true" > 2.< / strong > 程序结构< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-01.html" > < strong aria-hidden = "true" > 2.1.< / strong > 命名< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-02.html" > < strong aria-hidden = "true" > 2.2.< / strong > 声明< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-03.html" > < strong aria-hidden = "true" > 2.3.< / strong > 变量< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-04.html" > < strong aria-hidden = "true" > 2.4.< / strong > 赋值< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-05.html" > < strong aria-hidden = "true" > 2.5.< / strong > 类型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-06.html" > < strong aria-hidden = "true" > 2.6.< / strong > 包和文件< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch2/ch2-07.html" > < strong aria-hidden = "true" > 2.7.< / strong > 作用域< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3.html" > < strong aria-hidden = "true" > 3.< / strong > 基础数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-01.html" > < strong aria-hidden = "true" > 3.1.< / strong > 整型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-02.html" > < strong aria-hidden = "true" > 3.2.< / strong > 浮点数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-03.html" > < strong aria-hidden = "true" > 3.3.< / strong > 复数< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-04.html" > < strong aria-hidden = "true" > 3.4.< / strong > 布尔型< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-05.html" > < strong aria-hidden = "true" > 3.5.< / strong > 字符串< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch3/ch3-06.html" > < strong aria-hidden = "true" > 3.6.< / strong > 常量< / a > < / li > < / ol > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4.html" > < strong aria-hidden = "true" > 4.< / strong > 复合数据类型< / a > < / li > < li > < ol class = "section" > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-01.html" > < strong aria-hidden = "true" > 4.1.< / strong > 数组< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-02.html" > < strong aria-hidden = "true" > 4.2.< / strong > Slice< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-03.html" > < strong aria-hidden = "true" > 4.3.< / strong > Map< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-04.html" > < strong aria-hidden = "true" > 4.4.< / strong > 结构体< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-05.html" > < strong aria-hidden = "true" > 4.5.< / strong > JSON< / a > < / li > < li class = "chapter-item expanded " > < a href = "../ch4/ch4-06.html" > < strong aria-hidd
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2022-08-24 10:48:15 +00:00
< li > < em > KusonStack一站式可编程配置技术栈(Go): < a href = "https://github.com/KusionStack/kusion" > https://github.com/KusionStack/kusion< / a > < / em > < / li >
< li > < em > KCL 配置编程语言(Rust): < a href = "https://github.com/KusionStack/KCLVM" > https://github.com/KusionStack/KCLVM< / a > < / em > < / li >
< li > < em > 凹语言™: < a href = "https://github.com/wa-lang/wa" > https://github.com/wa-lang/wa< / a > < / em > < / li >
2022-08-04 06:59:33 +00:00
< / ul >
< hr >
< h2 id = "52-递归" > < a class = "header" href = "#52-递归" > 5.2. 递归< / a > < / h2 >
< p > 函数可以是递归的， ， ， ， ， ， < / p >
< p > 下文的示例代码使用了非标准包 golang.org/x/net/html ， ， ， ， ， < / p >
< p > 例子中调用golang.org/x/net/html的部分api如下所示。html.Parse函数读入一组bytes解析后， （ ） （ ） ， ， < name key='value' > 形式的结点。< / p >
< p > < u > < i > golang.org/x/net/html< / i > < / u > < / p >
< pre > < code class = "language-Go" > package html
type Node struct {
Type NodeType
Data string
Attr []Attribute
FirstChild, NextSibling *Node
}
type NodeType int32
const (
ErrorNode NodeType = iota
TextNode
DocumentNode
ElementNode
CommentNode
DoctypeNode
)
type Attribute struct {
Key, Val string
}
func Parse(r io.Reader) (*Node, error)
< / code > < / pre >
< p > main函数解析HTML标准输入， （ ） ， ： < / p >
< p > < u > < i > gopl.io/ch5/findlinks1< / i > < / u > < / p >
< pre > < code class = "language-Go" > // Findlinks1 prints the links in an HTML document read from standard input.
package main
import (
" fmt"
" os"
" golang.org/x/net/html"
)
func main() {
doc, err := html.Parse(os.Stdin)
if err != nil {
fmt.Fprintf(os.Stderr, " findlinks1: %v\n" , err)
os.Exit(1)
}
for _, link := range visit(nil, doc) {
fmt.Println(link)
}
}
< / code > < / pre >
< p > visit函数遍历HTML的节点树， ， < / p >
< pre > < code class = "language-Go" > // visit appends to links each link found in n and returns the result.
func visit(links []string, n *html.Node) []string {
if n.Type == html.ElementNode & & n.Data == " a" {
for _, a := range n.Attr {
if a.Key == " href" {
links = append(links, a.Val)
}
}
}
for c := n.FirstChild; c != nil; c = c.NextSibling {
links = visit(links, c)
}
return links
}
< / code > < / pre >
< p > 为了遍历结点n的所有后代结点， ， < / p >
< p > 让我们以Go的主页（ ） ， （ ） < / p >
< pre > < code > $ go build gopl.io/ch1/fetch
$ go build gopl.io/ch5/findlinks1
$ ./fetch https://golang.org | ./findlinks1
#
/doc/
/pkg/
/help/
/blog/
http://play.golang.org/
//tour.golang.org/
https://golang.org/dl/
//blog.golang.org/
/LICENSE
/doc/tos.html
http://www.google.com/intl/en/policies/privacy/
< / code > < / pre >
< p > 注意在页面中出现的链接格式，在之后我们会介绍如何将这些链接，根据根路径（ https://golang.org ） < / p >
< p > 在函数outline中， ， ， ， ， < / p >
< p > < u > < i > gopl.io/ch5/outline< / i > < / u > < / p >
< pre > < code class = "language-Go" > func main() {
doc, err := html.Parse(os.Stdin)
if err != nil {
fmt.Fprintf(os.Stderr, " outline: %v\n" , err)
os.Exit(1)
}
outline(nil, doc)
}
func outline(stack []string, n *html.Node) {
if n.Type == html.ElementNode {
stack = append(stack, n.Data) // push tag
fmt.Println(stack)
}
for c := n.FirstChild; c != nil; c = c.NextSibling {
outline(stack, c)
}
}
< / code > < / pre >
< p > 有一点值得注意： ， ， ， ， ； ， < / p >
< p > 下面是 https://golang.org 页面的简要结构:< / p >
< pre > < code > $ go build gopl.io/ch5/outline
$ ./fetch https://golang.org | ./outline
[html]
[html head]
[html head meta]
[html head title]
[html head link]
[html body]
[html body div]
[html body div]
[html body div div]
[html body div div form]
[html body div div form div]
[html body div div form div a]
...
< / code > < / pre >
< p > 正如你在上面实验中所见， ， < / p >
< p > 大部分编程语言使用固定大小的函数调用栈， ， ， ； ， ， ， （ ） < / p >
< p > < strong > 练习 5.1： < / strong > 修改findlinks代码中遍历n.FirstChild链表的部分， ， < / p >
< p > < strong > 练习 5.2： < / strong > 编写函数， < / p >
< p > < strong > 练习 5.3： < / strong > 编写函数输出所有text结点的内容。注意不要访问< code > < script> < / code > 和< code > < style> < / code > 元素，因为这些元素对浏览者是不可见的。< / p >
< p > < strong > 练习 5.4： < / strong > 扩展visit函数， ， < / p >
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