Highlight Lisp code in guide doc correctly

[skip ci]

Author: ubolonton

guide/book.toml

@@ -7,4 +7,5 @@ src = "src"
 [output.html]
 google-analytics = "UA-138609797-1"
 additional-css = ["custom.css"]
-preferred-dark-theme = "coal"
+additional-js = ["hljs-load-langs.js"]
+preferred-dark-theme = "coal"

guide/hljs-load-langs.js

@@ -0,0 +1,25 @@
+(function loadLangs() {
+  // mdbook is not very extensible yet. This is a workaround.
+  // In the long term, we should probably switch to org-mode.
+  // See https://github.com/rust-lang/mdBook/issues/657#issuecomment-377935449.
+
+  function highlight(lang) {
+    Array
+      .from(document.querySelectorAll("code.hljs.language-" + lang))
+      .forEach(function (block) { hljs.highlightBlock(block); })
+  }
+
+  function load(lang) {
+    var src = "//cdnjs.cloudflare.com/ajax/libs/highlight.js/9.15.9/languages/" + lang + ".min.js";
+    var s = document.createElement('script');
+    s.setAttribute('src', src);
+    s.setAttribute('type', 'text/javascript');
+    s.setAttribute('charset', 'utf-8');
+    s.onload = function() {
+      highlight(lang);
+    };
+    document.body.appendChild(s);
+  }
+
+  load('lisp');
+})();

guide/src/custom-types.md

@@ -42,7 +42,7 @@ fn init(env: &Env) -> Result<()> {
 }
 ```
 
-```emacs-lisp
+```lisp
 (let ((m (rs-hash-map/make)))
   (rs-hash-map/get m "a")     ; -> nil
 

guide/src/hello.md

@@ -55,7 +55,7 @@ ln -s libgreeting.dylib greeting.so
 ```
 
 Add `target/debug` to your Emacs's `load-path`, then load the module:
-```emacs-lisp
+```lisp
 (add-to-list 'load-path "/path/to/target/debug")
 (require 'greeting)
 (greeting-say-hello "Emacs")

guide/src/reloading.md

@@ -4,13 +4,13 @@ Live code reloading is very useful during development. However, Emacs does not s
 
 To use it, load it in Emacs:
 
-```emacs-lisp
+```lisp
 (require 'rs-module)
 ```
 
 Then use it to load other modules instead of `require` or `module-load`:
 
-```emacs-lisp
+```lisp
 ;; Will unload the old version of the module first.
 (rs-module/load "full/path/to/module.so")
 ```