good good study, day day up!

vendor/gopl.io/ch5/outline2/outline.go

@@ -0,0 +1,80 @@
+// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
+// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
+
+// See page 133.
+
+// Outline prints the outline of an HTML document tree.
+package main
+
+import (
+	"fmt"
+	"net/http"
+	"os"
+
+	"golang.org/x/net/html"
+)
+
+func main() {
+	for _, url := range os.Args[1:] {
+		outline(url)
+	}
+}
+
+func outline(url string) error {
+	resp, err := http.Get(url)
+	if err != nil {
+		return err
+	}
+	defer resp.Body.Close()
+
+	doc, err := html.Parse(resp.Body)
+	if err != nil {
+		return err
+	}
+
+	//!+call
+	forEachNode(doc, startElement, endElement)
+	//!-call
+
+	return nil
+}
+
+//!+forEachNode
+// forEachNode calls the functions pre(x) and post(x) for each node
+// x in the tree rooted at n. Both functions are optional.
+// pre is called before the children are visited (preorder) and
+// post is called after (postorder).
+func forEachNode(n *html.Node, pre, post func(n *html.Node)) {
+	if pre != nil {
+		pre(n)
+	}
+
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		forEachNode(c, pre, post)
+	}
+
+	if post != nil {
+		post(n)
+	}
+}
+
+//!-forEachNode
+
+//!+startend
+var depth int
+
+func startElement(n *html.Node) {
+	if n.Type == html.ElementNode {
+		fmt.Printf("%*s<%s>\n", depth*2, "", n.Data)
+		depth++
+	}
+}
+
+func endElement(n *html.Node) {
+	if n.Type == html.ElementNode {
+		depth--
+		fmt.Printf("%*s</%s>\n", depth*2, "", n.Data)
+	}
+}
+
+//!-startend