A Common Lisp syntax highlighter written in Javascript
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highlight-lisp - Common Lisp syntax highlighter

This is a syntax highlighter for Common Lisp written in Javascript. It is completely themable via CSS (themes included).

The purpose of this is to make it really easy to embed beautiful Common Lisp code into a website with minimal effort.

See the demo!


Usage is simple. You include highlight-lisp.js, link to one of the CSS themes, and call one of highlight-lisp's highlighting functions:

<!-- Put these in your document somewhere, probably in the head, although the <script>
     tag can probably go anywhere -->
<script type="text/javascript" src="/js/highlight-lisp/highlight-lisp.js"></script>
<link rel="stylesheet" href="/js/highlight-lisp/themes/github.css">


<!-- By default, the highlighter looks for code blocks with class="lisp" -->
<pre><code class="lisp">(defun test-syntax-highlighter ()
  "Docstring explaining what this function does."
  (let ((hash (make-hash-table :test #'equal)))

Once the HTML is set up, there are a few ways to initialize highlighting:

// automatically highlight all <code class="lisp">...</code> blocks

// specify a custom class name (instead of "lisp"):
HighlightLisp.highlight_auto({className: 'common-lisp'});

// highlight *every* code block
HighlightLisp.highlight_auto({className: null});

// manually highlight a code block
var code = document.getElementById('my-code-element');

Paren matching

You can now enable paren matching (on mouse hover):


This will go through all highlighted blocks of code and add mouseover/mouseout event listeners to all ('s and )'s that highlight the matching paren on hover.

What gets highlighted

  • Functions
    CSS class function
    Anything starting with (: (my-function ...)
    • Known functions
      CSS class function known
      Any function known by the highlighter: things like make-hash-table, when, format, etc
    • Special functions
      CSS class function known special
      Mainly let, let\*, lambda.
    • Symbol functions
      CSS class function symbol
      Example: #'my-function
    • Known symbol functions
      CSS class function symbol known
      Examples: #'equalp, #'format
  • Keywords
    CSS class keyword
    Anything starting with : like :this-is-a-keyword
    • Known keywords
      CSS class keyword known
      Known keywords are things like :hash-keys, :supersede, etc.
  • Symbols
    CSS class symbol
    Anything starting with ': 'my-symbol
  • Lambda-list operators
    CSS class lambda-list
    Things like &key, &body, etc.
  • Numbers
    CSS class number
    Any numbers: 69, -82.4, #xF047, #b11010
    • Integers
      CSS class number integer
      Simple numbers: 42, 867, etc. (no decimals)
    • Ratios
      CSS class number ratio
      Examples: 80/9, 23/4
    • Floats
      CSS class number float
      Numbers with a decimal: +47.82112, 32.9 3. .009
    • Hex
      CSS class number hex
      Hex numbers: #x8090, #xc001
    • Binary
      CSS class number binary
      Example: #b01101
  • Variables
    By themselves, variables remain unhighlighted
    • Known variables
      CSS class variable known
      Examples: *package*, *standard-output*, etc
    • Global variables
      CSS class variable global
      Any symbol surrounded by \*: *main-datastore*, *my-thread-local*, etc
    • Constants
      CSS class variable constant
      Any symbol surrounded by +: +dt+, +contant-time+, etc
  • nil/t
    CSS class nil
    Any standalone nil or t will get this class
  • Comments
    CSS class comment
    Example: ; this is a comment
  • Strings
    CSS class string
    Anthing inside ": "This is a string."
  • Parens
    CSS class list
    May be overkill, but any ( or ) characters are classified.

On that note, things that don't get highlighted/aren't properly highlighted:

  • Variables...things like let bindings or other symols within code that would be interpreted as variables. Highlighting these would most likely be prohibitive in terms of time (not the mention the return on investment). Feel free to patch!
  • Some number notations. For instance 0.44d0.
  • Multi-line comments #| ... |# are unsupported
  • Many constants (such as pi, internal-time-units-per-second) are classified as functions, not known variables. This is because I pulled the list out of my vim highlight script, and couldn't find a list of "Common Lisp standard variables" to cross reference with. I pulled out the ones I know of and put them into the known variables list, but there are no doubt more. If you see something that is a known variable but gets treated as a known function, please open a github issue.


Aren't there a bunch of Javascript syntax highlighters out there already?

Yes, but truth be told, most ignore lisp. You can write custom parsers for some of them, but the APIs they provide didn't work well enough for me. highlight.js has a very nice lisp highlighting mode, along with really nice themes, but I wanted more control over the process.

For instance, highlight-lisp started as a SyntaxHighlighter brush, but I quickly realized that because of the limitations of Javascript not allowing real lookbehind regular expressions, I needed more direct control over the search/replace process.

What I discovered was that given the proper tools, parsing lisp is easy (in fact, a cake walk after just releasing markdown.cl) and there's no need for a big highlighting framework. You plug in some regexes, slap some tags around certain things, and call it a day.


As always, MIT.