Solution for "A Tour of Go" Exercise #73 (This code does NOT work properly)

ex73.go

/*
Solution for "A Tour of Go" Exercise #73 (This code does NOT work properly)
http://tour.golang.org/#73
*/

package main

import (
    "fmt"
)

type Set map[interface{}]bool

type Fetcher interface {
    // Fetch returns the body of URL and
    // a slice of URLs found on that page.
    Fetch(url string) (body string, urls []string, err error)
}

func DoCrawl2(url string, depth int, fetcher Fetcher, crawled Set, ch chan string, errch chan error) {
    if depth <= 0 {
        return
    }
    if crawled[url] {
       return
    }
    body, urls, err := fetcher.Fetch(url)
    if err != nil {
        errch <- err
        return
    }

    crawled[url] = true
    ch <- fmt.Sprintf("found: %s %q", url, body)

    child_chs := make([]chan string, len(urls))
    child_errchs := make([]chan error, len(urls))
    for i, u := range urls {
        child_chs[i] = make(chan string)
        child_errchs[i] = make(chan error)
        go DoCrawl(u, depth-1, fetcher, crawled, child_chs[i], child_errchs[i])
    }

    for _, c := range child_chs {
        for u := range c {
              ch <- u
        }
        }
    for _, c := range child_errchs {
        for e := range c {
            errch <- e
        }
    }
    return
}

func DoCrawl(url string, depth int, fetcher Fetcher, crawled Set, ch chan string, errch chan error) {
    DoCrawl2(url, depth, fetcher, crawled, ch, errch)
    close(ch)
    close(errch)
}

func Crawl(url string, depth int, fetcher Fetcher, ch chan string, errch chan error) {
    crawled := make(Set)
    DoCrawl(url, depth, fetcher, crawled, ch, errch)
}

func main() {
    ch, errch := make(chan string), make(chan error)
    go Crawl("http://golang.org/", 4, fetcher, ch, errch)

    fmt.Println("Fetched:")
    for x := range ch {
        fmt.Println(x)
            for x := range ch {
        fmt.Println(x)
    }
    fmt.Println("Error:")
    for x := range errch {
        fmt.Println(x.Error())
    }
}

// fakeFetcher is Fetcher that returns canned results.
type fakeFetcher map[string]*fakeResult

type fakeResult struct {
    body string
    urls []string
}

func (f fakeFetcher) Fetch(url string) (string, []string, error) {
    if res, ok := f[url]; ok {
        return res.body, res.urls, nil
    }
    return "", nil, fmt.Errorf("not found: %s", url)
}

// fetcher is a populated fakeFetcher.
var fetcher = fakeFetcher{
    "http://golang.org/": &fakeResult{
        "The Go Programming Language",
        []string{
            "http://golang.org/pkg/",
            "http://golang.org/cmd/",
        },
    },
    "http://golang.org/pkg/": &fakeResult{
        "Packages",
        []string{
            "http://golang.org/",
                        "http://golang.org/cmd/",
            "http://golang.org/pkg/fmt/",
            "http://golang.org/pkg/os/",
        },
    },
    "http://golang.org/pkg/fmt/": &fakeResult{
        "Package fmt",
        []string{
            "http://golang.org/",
            "http://golang.org/pkg/",
        },
    },
    "http://golang.org/pkg/os/": &fakeResult{
        "Package os",
        []string{
            "http://golang.org/",
            "http://golang.org/pkg/",
        },
    },
}