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#Markdown parser written in Clojure

Demo

You can try out the parser here.

Installation

A markdown parser that compiles to both Clojure and ClojureScript.

Clojars Project

Note: markdown-clj requires Clojure 1.2+ to run.

Usage Clojure

Markdown-clj can be invoked either by calling md-to-html or md-to-html-string functions.

The md-to-html function accepts an input containing Markdown markup and an output where the resulting HTML will be written. The input and output parameters will be passed to a reader and a writer respectively:

(ns foo
  (:use markdown.core))

(md-to-html "input.md" "output.html")

(md-to-html (input-stream "input.md") (output-stream "test.txt"))

The md-to-html-string function accepts a string with markdown content and returns a string with the resulting HTML:

(md-to-html-string "# This is a test\nsome code follows\n```clojure\n(defn foo [])\n```")
<h1> This is a test</h1>some code follows<pre><code class="clojure">&#40;defn foo &#91;&#93;&#41;
</code></pre>

Both md-to-html and md-to-html-string can accept optional parameters:

Specifying :heading-anchors will create anchors for the heading tags, eg:

(markdown/md-to-html-string "###foo bar BAz" :heading-anchors true)
<h3><a name=\"heading\" class=\"anchor\" href=\"#foo&#95;bar&#95;baz\"></a>foo bar BAz</h3>

The code blocks default to a highlight.js compatible format of:

<pre><code class="clojure">some code</code></pre>

Specifying :code-style will override the default code class formatting for code blocks, eg:

(md-to-html-string "# This is a test\nsome code follows\n```clojure\n(defn foo [])\n```"
                   :code-style #(str "class=\"brush: " % "\""))
<h1> This is a test</h1>some code follows<pre><code class="brush: clojure">
&#40;defn foo &#91;&#93;&#41;
</code></pre>

Additional transformers can be specified using the :custom-transformers key. A transformer function must accept two arguments. First argument is the string representing the current line and the second is the map representing the current state.

The default state keys are:

  • :code - inside a code section
  • :codeblock - inside a code block
  • :eof - end of file
  • :heading - in a heading
  • :hr - in a horizontal line
  • :lists - inside a list
  • :blockquote - inside a blockquote
  • :paragraph? - in a paragraph?
  • :last-line-empty? - was last line an empty line?

For example, if we wanted to add a transformer that would capitalize all text we could do the following:

(defn capitalize [text state]
  [(.toUpperCase text) state])

(markdown/md-to-html-string "#foo" :custom-transformers [capitalize])
<H1>FOO</H1>

Alternatively, you could provide a custom set of transformers to replace the default transformers using the :replacement-transformers key.

(markdown/md-to-html-string "#foo" :replacement-transformers [capitalize])

This can also be used to add preprocessor transformers. For example, if we wanted to sanitize any image links we could do the following:

(use 'markdown.transformers 'markdown.core)

(defn escape-images [text state]
  [(clojure.string/replace text #"(!\[.*?\]\()(.+?)(\))" "") state])

(markdown/md-to-html-string
  "foo ![Alt text](/path/to/img.jpg \"Optional Title\") bar [text](http://test)"
  :replacement-transformers (cons escape-images transformer-vector))
"<p>foo  bar <a href='http://test'>text</a></p>"

Usage ClojureScript

The ClojureScript portion works the same as above except that the entry function is called md->html. It accepts a string followed by the options as its input, and returns the resulting HTML string:

(ns myscript
  (:require [markdown.core :refer [md->html]]))

(.log js/console
  (md->html "##This is a heading\nwith a paragraph following it"))

(.log js/console
  (md->html "# This is a test\nsome code follows\n```clojure\n(defn foo [])\n```"
               :code-style #(str "class=\"" % "\"")))

Usage JavaScript

console.log(markdown.core.mdToHtml("##This is a heading\nwith a paragraph following it"));

Supported syntax

Control characters can be escaped using \

\\ backslash
\` backtick
\* asterisk
\_ underscore
\{ curly braces
\}
\[ square brackets
\]
\( parentheses
\)
\# hash mark
\+ plus sign
\- minus sign (hyphen)
\. dot
\! exclamation mark

Basic Elements

Blockquote, Strong, Bold, Emphasis, Italics, Heading, Line, Linebreak, Paragraph, Strikethrough

Links

Image, Link

Automatic Links

This is a shortcut style for creating “automatic” links for URLs and email addresses:

<http://example.com/>

will be turned this into:

<a href="http://example.com/">http://example.com/</a>

Automatic links for email addresses work similarly, except that they are hex encoded:

will be turned into:

<a href=\"&#x61&#x64&#x64&#x72&#x65&#x73&#x73&#x40&#x65&#x78&#x61&#x6d&#x70&#x6c&#x65&#x2e&#x63&#x6f&#x6d\">&#x61&#x64&#x64&#x72&#x65&#x73&#x73&#x40&#x65&#x78&#x61&#x6d&#x70&#x6c&#x65&#x2e&#x63&#x6f&#x6d</a>

Lists

Ordered List, Unordered List

Code

Code Block, Indented Code, Inline Code


Heading

the number of hashes indicates the level of the heading

# Heading

##Sub-heading

### Sub-sub-heading

headings can also be defined using = and - for h1 and h2 respectively

Heading 1
=========

Heading 2
---------

Line

***

* * *

*****

- - -

______

Linebreak

If a line ends with two or more spaces a <br /> tag will be inserted at the end.

Emphasis

*foo*

Italics

_foo_

Strong

**foo**

Bold

__foo__

Blockquote

> prefixes regular blockquote paragraphs. >- prefixes a blockquote footer that can be used for author attribution.

>This is a blockquote
with some content

>this is another blockquote

> Everyone thinks of changing the world,
but no one thinks of changing himself.
>- Leo Tolstoy

Paragraph

This is a paragraph, it's
split into separate lines.

This is another paragraph.

Unordered List

indenting an item makes it into a sublist of the item above it, ordered and unordered lists can be nested within one another. List items can be split over multiple lines.

* Foo
* Bar
 * Baz
* foo
* bar

   * baz
     1. foo
     2. bar
        more content
        ## subheading
        ***
        **strong text** in the list

   * fuzz

      * blah
      * blue
* brass

Ordered List

1. Foo
2. Bar
3. Baz

Inline Code

Any special characters in code will be escaped with their corresponding HTML codes.

Here's some code `x + y = z` that's inlined.

Code block

Using three backquotes indicates a start of a code block, the next three backquotes ends the code block section. Optionally, the language name can be put after the backquotes to produce a tag compatible with highlight.js, eg:

```clojure

(defn foo [bar] "baz")

```

Indented Code

indenting by at least 4 spaces creates a code block

some
code
here

note: XML is escaped in code sections

Strikethrough

~~foo~~

Superscript

a^2 + b^2 = c^2

Link

[github](http://github.com)

Image

![Alt text](http://server/path/to/img.jpg)
![Alt text](/path/to/img.jpg "Optional Title")

Image Link

[![Continuous Integration status](https://secure.travis-ci.org/yogthos/markdown-clj.png)](http://travis-ci.org/yogthos/markdown-clj)

Limitations

The parser reads the content line by line, this means that tag content is not allowed to span multiple lines.

License

Copyright (C) 2012 Yogthos

Distributed under the Eclipse Public License, the same as Clojure.

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Markdown parser in Clojure

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