earmark

# Earmark—A Pure Elixir Markdown Processor
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<!-- moduledoc: Earmark -->
## Dependency
    { :earmark, "> x.y.z" }
## Usage
### API
    * `Earmark.as_html`
      {:ok, html_doc, []}                = Earmark.as_html(markdown)
      {:error, html_doc, error_messages} = Earmark.as_html(markdown)
    * `Earmark.as_html!`
      html_doc = Earmark.as_html!(markdown, options)
      Any error messages are printed to _stderr_.
#### Options:
#
Options can be passed into `as_html` or `as_html!` according to the documentation.
      html_doc = Earmark.as_html!(markdown)
      html_doc = Earmark.as_html!(markdown, options)
Formats the error_messages returned by `as_html` and adds the filename to each.
Then prints them to stderr and just returns the html_doc
### Command line
    $ mix escript.build
    $ ./earmark file.md
Some options defined in the `Earmark.Options` struct can be specified as command line switches.
Use
    $ ./earmark --help
to find out more, but here is a short example
    $ ./earmark --smartypants false --code-class-prefix "a- b-" file.md
will call
    Earmark.as_html!( ..., %Earmark.Options{smartypants: false, code_class_prefix: "a- b-"})
## Supports
Standard [Gruber markdown][gruber].
[gruber]: <http://daringfireball.net/projects/markdown/syntax>
## Extensions
### Tables
Github Flavored Markdown tables are supported
        State | Abbrev | Capital
        ----: | :----: | -------
        Texas | TX     | Austin
        Maine | ME     | Augusta
Tables may have leading and trailing vertical bars on each line
        | State | Abbrev | Capital |
        | ----: | :----: | ------- |
        | Texas | TX     | Austin  |
        | Maine | ME     | Augusta |
Tables need not have headers, in which case all column alignments
default to left.
        | Texas | TX     | Austin  |
        | Maine | ME     | Augusta |
Currently we assume there are always spaces around interior vertical
bars. It isn't clear what the expectation is.
### Adding HTML attributes with the IAL extension
HTML attributes can be added to any block-level element. We use
the Kramdown syntax: add the line `{:` _attrs_ `}` following the block.
_attrs_ can be one or more of:
* `.className`
* `#id`
* name=value, name="value", or name='value'
Malformed attributes are ignored and a warning is issued to stderr.
If you need to render IAL-like test verbatim escape it:
`{:alpha, 42}`
This of course is not necessary in code blocks or text lines
containing an IAL-like string, as in
`the returned tuple should be {:error, "I wish you hadn't done that"}`
For example:
        # Warning
        {: .red}
        Do not turn off the engine
        if you are at altitude.
        {: .boxed #warning spellcheck="true"}
## Limitations
* Nested block-level HTML is correctly handled only if each HTML
  tag appears on its own line. So
        <div>
        <div>
        hello
        </div>
        </div>
  will work. However. the following won't
        <div><div>
        hello
        </div></div>
* John Gruber's tests contain an ambiguity when it comes to
  lines that might be the start of a list inside paragraphs.
  One test says that
        This is the text
        * of a paragraph
        that I wrote
  is a single paragraph. The "*" is not significant. However, another
  test has
        *   A list item
            * an another
  and expects this to be a nested list. But, in reality, the second could just
  be the continuation of a paragraph.
  I've chosen always to use the second interpretation—a line that looks like
  a list item will always be a list item.
* Rendering of block and inline elements.
  Block or void HTML elements that are at the absolute beginning of a line end
  the preceding paragraph.
  Thusly
        mypara
        <hr>
  Becomes
        <p>mypara</p>
        <hr>
  While
        mypara
         <hr>
  will be transformed into
        <p>mypara
         <hr></p>
## Integration
### Syntax Highlightning
All backquoted or fenced code blocks with a language string are rendered with the given
language as a _class_ attribute of the _code_ tag.
For example:
      ```elixir
         @tag :hello
      ```
will be rendered as
       <pre><code class="elixir">...
If you want to integrate with a syntax highlighter with different conventions you can add more classes by specifying prefixes that will be
put before the language string.
Prism.js for example needs a class `language-elixir`. In order to achieve that goal you can add `language-`
as a `code_class_prefix` to `Earmark.Options`.
In the following example we want more than one additional class, so we add more prefixes.
      Earmark.as_html!(..., %Earmark.Options{code_class_prefix: "lang- language-"})
which is rendering
       <pre><code class="elixir lang-elixir language-elixir">...
As for all other options `code_class_prefix` can be passed into the `earmark` executable as follows:
      earmark --code-class-prefix "language- lang-" ...
## Security
  Please be aware that Markdown is not a secure format. It produces
  HTML from Markdown and HTML. It is your job to sanitize and or
  filter the output of `Markdown.html` if you cannot trust the input
  and are to serve the produced HTML on the Web.
## Author
Copyright © 2014 Dave Thomas, The Pragmatic Programmers
@/+pragdave,  dave@pragprog.com
Licensed under the same terms as Elixir, which is Apache 2.0.
<!-- endmoduledoc: Earmark -->
# Details
<!-- doc: Earmark.as_html -->
Given a markdown document (as either a list of lines or
a string containing newlines), returns a tuple containing either
`{:ok, html_doc}`, or `{:error, html_doc, error_messages}`
Where `html_doc` is an HTML representation of the markdown document and
`error_messages` is a list of strings representing information concerning
the errors that occurred during parsing.
The options are a `%Earmark.Options{}` structure:
* `renderer`: ModuleName
  The module used to render the final document. Defaults to
  `Earmark.HtmlRenderer`
* `gfm`: boolean
  True by default. Turns on Github Flavored Markdown extensions
* `breaks`: boolean
  Only applicable if `gfm` is enabled. Makes all line breaks
  significant (so every line in the input is a new line in the
  output.
* `smartypants`: boolean
  Turns on smartypants processing, so quotes become curly, two
  or three hyphens become en and em dashes, and so on. True by
  default.
So, to format the document in `original` and disable smartypants,
you'd call
    alias Earmark.Options
    Earmark.as_html(original, %Options{smartypants: false})
<!-- enddoc: Earmark.as_html -->
## Plugins
<!-- moduledoc: Earmark.Plugin -->
Plugins are modules that implement a render function. Right now that is `as_html`.
### API
#### Plugin Registration
When invoking `Earmark.as_html(some_md, options)` we can register plugins inside the `plugins` map, where
each plugin is a value pointed to by the prefix triggering it.
Prefixes are appended to `"$$"` and lines starting by that string will be rendered by the registered plugin.
`%Earmark.Options{plugins: %{"" => CommentPlugin}}` would trigger the `CommentPlugin` for each block of
lines prefixed by `$$`, while `%Earmark.Options{plugins: %{"cp" => CommentPlugin}}` would do the same for
blocks of lines prefixed by `$$cp`.
Please see the documentation of `Plugin.define` for a convenience function that helps creating the necessary
`Earmark.Options` structs for the usage of plugins.
#### Plugin Invocation
`as_html` (or other render functions in the future) is invoked with a list of pairs containing the text
and line number of the lines in the block. As an example, if our plugin was registered with the default prefix
of `""` and the markdown to be converted was:
      # Plugin output ahead
      $$ line one
      $$
      $$ line two
`as_html` would be invoked as follows:
      as_html([{"line one", 2}, {"", 3}, {"line two", 4})
#### Plugin Output
Earmark's render function will invoke the plugin's render function as explained above. It can then integrate the
return value of the function into the generated rendering output if it complies to the following criteria.
1. It returns a string
1. It returns a list of strings
1. It returns a pair of lists containing a list of strings and a list of error/warning tuples.
Where the tuples are of the form `{:error | :warning, line_number, descriptive_text}`
#### A complete example
      iex> defmodule MyPlug do
      ...>   def as_html(lines) do
      ...>     # to demonstrate the three possible return values
      ...>     case render(lines) do
      ...>       {[line], []} -> line
      ...>       {lines, []} -> lines
      ...>       tuple       -> tuple
      ...>     end
      ...>   end
      ...>
      ...>   defp render(lines) do
      ...>     Enum.map(lines, &render_line/1) |> Enum.partition(&ok?/1)
      ...>   end
      ...>
      ...>   defp render_line({"", _}), do: "<hr/>"
      ...>   defp render_line({"line one", _}), do: "<p>first line</p>\n"
      ...>   defp render_line({line, lnb}), do: {:error, lnb, line}
      ...>
      ...>   defp ok?({_, _, _}), do: false
      ...>   defp ok?(_), do: true
      ...> end
      ...>
      ...> lines = [
      ...>   "# Plugin Ahead",
      ...>   "$$ line one",
      ...>   "$$",
      ...>   "$$ line two",
      ...> ]
      ...> Earmark.as_html(lines, Earmark.Plugin.define(MyPlug))
      {:error, "<h1>Plugin Ahead</h1>\n<p>first line</p>\n<hr/>", [{ :error, 4, "line two"}]}
#### Plugins, reusing Earmark
As long as you avoid endless recursion there is absolutely no problem to call `Earmark.as_html` in your plugin, consider the following
example in which the plugin will parse markdown and render html verbatim (which uis stupid, that is what Earmark already does for you,
but just to demonstrate the possibilities):
      iex> defmodule Again do
      ...>   def as_html(lines) do
      ...>     text_lines = Enum.map(lines, fn {str, _} -> str end)
      ...>     {_, html, errors} = Earmark.as_html(text_lines)
      ...>     { Enum.join([html | text_lines]), errors }
      ...>   end
      ...> end
      ...>  lines = [
      ...>    "$$a * one",
      ...>    "$$a * two",
      ...>  ]
      ...>  Earmark.as_html(lines, Earmark.Plugin.define({Again, "a"}))
      {:ok, "<ul>\n<li>one\n</li>\n<li>two\n</li>\n</ul>\n* one* two", []}
<!-- endmoduledoc: Earmark.Plugin -->
## Author
Copyright © 2014 Dave Thomas, The Pragmatic Programmers
@/+pragdave,  dave@pragprog.com
# LICENSE
Same as Elixir, which is Apache License v2.0. Please refer to [LICENSE](LICENSE) for details.