commonmark-hiccup

A small Clojure library for converting CommonMark markdown to HTML. It is designed to make the HTML output as configurable as possible, relying on Hiccup as an intermediary representation.

Installation

Add the following dependency to project.clj:

[commonmark-hiccup "0.2.0"]

Documentation

commonmark-hiccup uses the commonmark-java parser and implements its own renderer, which transforms the CommonMark AST to Hiccup-compatible Clojure data structures. It then uses Hiccup to render them to their final HTML representation.

commonmark-hiccup is built for configurability, not performance. I use it to render static content for different web sites, each with different requirements for how paragraphs, code blocks etc. should look like.

Usage

You can convert a markdown string to HTML using markdown->html:

user=> (require '[commonmark-hiccup.core :refer [markdown->html]])
nil
user=> (markdown->html "This is a *test*.")
"<p>This is a <em>test</em>.</p>"

You can pass a configuration to the converter to tweak the output. This example renders paragraphs without the surrounding <p></p> tags:

user=> (let [config (update-in commonmark-hiccup.core/default-config
                               [:renderer :nodes org.commonmark.node.Paragraph]
                               (constantly :content))]
         (markdown->html config "This is a *test*."))
"This is a <em>test</em>."

Configuration

The default configuration defines the Hiccup snippets to which the different CommonMark AST nodes are rendered:

(def default-config
  {:renderer {:nodes {org.commonmark.node.Document          :content
                      org.commonmark.node.Heading           ['(:h :node-level) :content]
                      org.commonmark.node.Paragraph         [:p :content]
                      org.commonmark.node.Text              :node-literal
                      org.commonmark.node.BulletList        [:ul :content]
                      org.commonmark.node.OrderedList       [:ol {:start :node-startNumber} :content]
                      org.commonmark.node.ListItem          [:li :content]
                      org.commonmark.node.BlockQuote        [:blockquote :content]
                      org.commonmark.node.HtmlBlock         :node-literal
                      org.commonmark.node.HtmlInline        :node-literal
                      org.commonmark.node.FencedCodeBlock   [:pre [:code {:class :node-info} :node-literal]]
                      org.commonmark.node.IndentedCodeBlock [:pre [:code :node-literal]]
                      org.commonmark.node.Code              [:code :node-literal]
                      org.commonmark.node.Link              [:a {:href :node-destination} :content]
                      org.commonmark.node.Image             [:img {:src   :node-destination
                                                                   :alt   :text-content
                                                                   :title :node-title}]
                      org.commonmark.node.Emphasis          [:em :content]
                      org.commonmark.node.StrongEmphasis    [:strong :content]
                      org.commonmark.node.ThematicBreak     [:hr]
                      org.commonmark.node.SoftLineBreak     " "
                      org.commonmark.node.HardLineBreak     [:br]}}
   :parser   {:extensions nil}})

The :nodes map uses commonmark-java node classes as keys. The values are just Clojure data structures. Some keywords and lists are replaced during rendering:

• All keywords prefixed with :node- are replaced with the respective property of the rendered node (e.g. :node-literal for org.commonmark.node.HtmlBlock is replaced with the value returned by HtmlBlock::getLiteral).
• Some keywords are special: :content is replaced with the rendered content of the current node's children; :text-content is replaced with the concatenated content of all org.commonmark.node.Text child nodes.
• List elements are joined to strings. This is useful for rendering node properties as part of a longer string. ['(:h :node-level) :content] uses the level property of the Heading node to render the appropriate HTML tag (e.g. <h1></h1> for level 1 headings).

For the available properties for each node type, refer to the commonmark-java sources.

Extensions

CommonMark extensions can be added to the parser by including them in the [:parser :extensions] list.

For example, to add the support for GFM tables:

1. Add the dependency to your project

[com.atlassian.commonmark/commonmark-ext-gfm-tables "..."]

2. Add the extension to your config along with the new renderers

(require '[commonmark-hiccup.core :as md])
(def my-config
     (-> md/default-config
         (update-in [:parser :extensions] conj
                    (org.commonmark.ext.gfm.tables.TablesExtension/create))
         (update-in [:renderer :nodes] merge
                    {org.commonmark.ext.gfm.tables.TableBlock [:table :content]
                     org.commonmark.ext.gfm.tables.TableHead  [:thead :content]
                     org.commonmark.ext.gfm.tables.TableBody  [:tbody :content]
                     org.commonmark.ext.gfm.tables.TableRow   [:tr :content]
                     org.commonmark.ext.gfm.tables.TableCell  [:td :content]})))

(md/markdown->hiccup mt-config "|head1|head2|
|---|---|
|foo|bar|")
=> ([:table
     ([:thead ([:tr ([:td ("head1")] [:td ("head2")])])]
      [:tbody ([:tr ([:td ("foo")] [:td ("bar")])])])])

License

Copyright © 2017 Axel Schüssler

Distributed under the Eclipse Public License either version 1.0 or (at your option) any later version.