• css selectors for go Yet another package implementing a css selector compiler for go - see e.g. [[https://github.com/ericchiang/css/][github.com/ericchiang/css]] and [[https://github.com/andybalholm/cascadia][github.com/andybalholm/cascadia]] for prior art.

Differentiating features:

• Extensible (allows for user defined pseudo-classes/functions, matchers and combinators)
• Conversion from compiled Selector back to Selector string
• Small (~800 LOC), simple/modular (separation into lexing, parsing & selecting) and fast (benchmarks put it head to head with cascadia)

#+begin_src go import ( "log" "strings"

"github.com/niklasfasching/x/css"
"golang.org/x/net/html"

)

func main() { doc, _ := html.Parse(strings.NewReader( <p> <span class="a">apple</span> <span class="b">banana</span> <span class="b">berry</span> <span class="c">pear</span> </p> ))

selector := css.MustCompile("p > span.b")
nodes := css.All(selector, doc)
for _, n := range nodes {
	var s strings.Builder
	html.Render(&s, n)
	log.Println(s.String())
}
// <span class="b">banana</span>
// <span class="b">berry</span>

log.Printf("Converted back to string: %s", selector) // Converted back to string: p > span.b

// easy to add your own custom pseudo classes, pseudo functions, matchers & combinators
css.PseudoClasses["my-pseudo-p"] = func(n *html.Node) bool { return n.Data == "p" },
selector = css.MustCompile(":my-pseudo-p")
var s strings.Builder
html.Render(&s, css.First(selector, doc))
log.Println(s.String()) // <p>...</p>

} #+end_src

** but why? for fun

• It seemed easy enough to do
• I've been really into writing parsers lately and this felt a belt more complicated than a lisp
• I enjoy web scraping and wanted to learn more about underlying concepts
• I wanted to learn more about profiling go - and this seemed like a good playground
• The existing css libraries cannot be extended / customized

• resources

• https://github.com/andybalholm/cascadia
• https://github.com/ericchiang/css
• https://github.com/fb55/css-select
• [[https://webcache.googleusercontent.com/search?q=cache:OaB_kAprZssJ:https://www.w3.org/TR/2018/CR-selectors-3-20180130/][https://www.w3.org/TR/2018/CR-selectors-3-20180130/]]