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EarmarkParser A Pure Elixir Markdown Parser

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Table Of Contents

Usage

EarmarkParser

API

EarmarkParser.as_ast

This is the structure of the result of as_ast.

{:ok, ast, []}                   = EarmarkParser.as_ast(markdown)
{:ok, ast, deprecation_messages} = EarmarkParser.as_ast(markdown)
{:error, ast, error_messages}    = EarmarkParser.as_ast(markdown)

For examples see the functiondoc below.

Options

Options can be passed into as_ast/2 according to the documentation of EarmarkParser.Options.

{status, ast, errors} = EarmarkParser.as_ast(markdown, options)

Supports

Standard Gruber markdown.

Extensions

Links

Links supported by default

Oneline HTML Link tags
    iex(1)> EarmarkParser.as_ast(~s{<a href="href">link</a>})
    {:ok, [{"a", [{"href", "href"}], ["link"], %{verbatim: true}}], []}
Markdown links

New style ...

    iex(2)> EarmarkParser.as_ast(~s{[title](destination)})
    {:ok,  [{"p", [], [{"a", [{"href", "destination"}], ["title"], %{}}], %{}}], []}

and old style

    iex(3)> EarmarkParser.as_ast("[foo]: /url \"title\"\n\n[foo]\n")
    {:ok, [{"p", [], [{"a", [{"href", "/url"}, {"title", "title"}], ["foo"], %{}}], %{}}], []}

Autolinks

    iex(4)> EarmarkParser.as_ast("<https://elixir-lang.com>")
    {:ok, [{"p", [], [{"a", [{"href", "https://elixir-lang.com"}], ["https://elixir-lang.com"], %{}}], %{}}], []}

Additional link parsing via options

Pure links

N.B. that the pure_links option is true by default

    iex(5)> EarmarkParser.as_ast("https://github.com")
    {:ok, [{"p", [], [{"a", [{"href", "https://github.com"}], ["https://github.com"], %{}}], %{}}], []}

But can be deactivated

    iex(6)> EarmarkParser.as_ast("https://github.com", pure_links: false)
    {:ok, [{"p", [], ["https://github.com"], %{}}], []}

Wikilinks...

are disabled by default

    iex(7)> EarmarkParser.as_ast("[[page]]")
    {:ok, [{"p", [], ["[[page]]"], %{}}], []}

and can be enabled

    iex(8)> EarmarkParser.as_ast("[[page]]", wikilinks: true)
    {:ok, [{"p", [], [{"a", [{"href", "page"}], ["page"], %{wikilink: true}}], %{}}], []}

Sub and Sup HTML Elements

This feature is not enabled by default but can be enabled with the option sub_sup: true

Therefore we will get

    iex(9)> EarmarkParser.as_ast("H~2~O or a^n^ + b^n^ = c^n^")
    {:ok, [{"p", [], ["H~2~O or a^n^ + b^n^ = c^n^"], %{}}], []}

But by specifying sub_sup: true

    iex(10)> EarmarkParser.as_ast("H~2~O or a^n^ + b^n^ = c^n^", sub_sup: true)
    {:ok, [{"p", [], ["H", {"sub", [], ["2"], %{}}, "O or a", {"sup", [], ["n"], %{}}, " + b", {"sup", [], ["n"], %{}}, " = c", {"sup", [], ["n"], %{}}], %{}}], []}

Mathematical expressions

Note: math syntax within Markdown is not standardized, so this option is a subject to change in future releases.

This feature is not enabled by default but can be enabled with the option math: true.

When enabled, LaTeX formatted math can be written within Markdown. For more information, see LaTeX/Mathematics in Wikibooks.

Inline expressions

Inline-style expression can be written by surrounding the expression with dollar symbols ($).

iex> EarmarkParser.as_ast("$x = 1$", math: true)
{:ok, [{"p", [], [{"code", [{"class", "math-inline"}], ["x = 1"], %{line: 1}}], %{}}], []}

There must be no space between $ and the surrounded expression. If you want to use a dollar sign in the same line as a math expression, you can escape the dollar with backslash (\\$).

Expressions as blocks

Display-style expression can be written by surrounding the expression with two dollar signs ($$).

iex> EarmarkParser.as_ast("$$x = 1$$", math: true)
{:ok, [{"p", [], [{"code", [{"class", "math-display"}], ["x = 1"], %{line: 1}}], %{}}], []}

Github Flavored Markdown

GFM is supported by default, however as GFM is a moving target and all GFM extension do not make sense in a general context, EarmarkParser does not support all of it, here is a list of what is supported:

Strike Through

    iex(11)> EarmarkParser.as_ast("~~hello~~")
    {:ok, [{"p", [], [{"del", [], ["hello"], %{}}], %{}}], []}

GFM Tables

Are not enabled by default

    iex(12)> as_ast("a|b\\n-|-\\nc|d\\n")
    {:ok, [{"p", [], ["a|b\\n-|-\\nc|d\\n"], %{}}], []}

But can be enabled with gfm_tables: true

    iex(13)> as_ast("a|b\n-|-\nc|d\n", gfm_tables: true)
    {:ok,
      [
        {
          "table",
          [],
          [
            {"thead", [], [{"tr", [], [{"th", [{"style", "text-align: left;"}], ["a"], %{}}, {"th", [{"style", "text-align: left;"}], ["b"], %{}}], %{}}], %{}},
            {"tbody", [], [{"tr", [], [{"td", [{"style", "text-align: left;"}], ["c"], %{}}, {"td", [{"style", "text-align: left;"}], ["d"], %{}}], %{}}], %{}}
          ],
          %{}
        }
      ],
      []}

Syntax Highlighting

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:

    iex(14)> [
    ...(14)>    "```elixir",
    ...(14)>    " @tag :hello",
    ...(14)>    "```"
    ...(14)> ] |> as_ast()
    {:ok, [{"pre", [], [{"code", [{"class", "elixir"}], [" @tag :hello"], %{}}], %{}}], []}

will be rendered as shown in the doctest above.

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 EarmarkParser.Options.

In the following example we want more than one additional class, so we add more prefixes.

    iex(15)> [
    ...(15)>    "```elixir",
    ...(15)>    " @tag :hello",
    ...(15)>    "```"
    ...(15)> ] |> as_ast(%EarmarkParser.Options{code_class_prefix: "lang- language-"})
    {:ok, [{"pre", [], [{"code", [{"class", "elixir lang-elixir language-elixir"}], [" @tag :hello"], %{}}], %{}}], []}

Footnotes

N.B. Footnotes are disabled by default, use as_ast(..., footnotes: true) to enable them

Footnotes are now a superset of GFM Footnotes. This implies some changes

  • Footnote definitions ([^footnote_id]) must come at the end of your document (GFM)

  • Footnotes that are not referenced are not rendered anymore (GFM)

  • Footnote definitions can contain any markup with the exception of footnote definitions

    # iex(16)> markdown = [
# ...(16)> "My reference[^to_footnote]",
# ...(16)> "",
# ...(16)> "[^1]: I am not rendered",
# ...(16)> "[^to_footnote]: Important information"]
# ...(16)> {:ok, ast, []} = as_ast(markdown, footnotes: true)
# ...(16)> ast
# [
#   {"p", [], ["My reference",
#     {"a",
#     [{"href", "#fn:to_footnote"}, {"id", "fnref:to_footnote"}, {"class", "footnote"}, {"title", "see footnote"}],
#     ["to_footnote"], %{}}
#   ], %{}},
#   {"div",
#   [{"class", "footnotes"}],
#   [{"hr", [], [], %{}},
#     {"ol", [],
#     [{"li", [{"id", "fn:to_footnote"}],
#       [{"a", [{"title", "return to article"}, {"class", "reversefootnote"}, {"href", "#fnref:to_footnote"}], ["&#x21A9;"], %{}},
#         {"p", [], ["Important information"], %{}}], %{}}
#     ], %{}}], %{}}
# ]

For more complex examples of footnotes, please refer to these tests

Breaks

Hard linebreaks are disabled by default

        iex(17)> ["* a","  b", "c"]
        ...(17)> |> as_ast()
        {:ok,
          [{"ul", [], [{"li", [], ["a\nb\nc"], %{}}], %{}}],
          []}
But can be enabled with `breaks: true`

        iex(18)> ["* a","  b", "c"]
        ...(18)> |> as_ast(breaks: true)
        {:ok, [{"ul", [], [{"li", [], ["a", {"br", [], [], %{}}, "b", {"br", [], [], %{}}, "c"], %{}}], %{}}], []}

Enabling all options that are disabled by default

Can be achieved with the `all: true` option

        iex(19)> [
        ...(19)> "a^n^",
        ...(19)> "b~2~",
        ...(19)> "[[wikilink]]"]
        ...(19)> |> as_ast(all: true)
        {:ok, [
          {"p", [], ["a", {"sup", [], ["n"], %{}}, {"br", [], [], %{}}, "b", {"sub", [], ["2"], %{}}, {"br", [], [], %{}}, {"a", [{"href", "wikilink"}], ["wikilink"], %{wikilink: true}}], %{}}
          ],
          []}

Tables

Are supported as long as they are preceded by an empty line.

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 unless there are exterior bars.

However in order to be more GFM compatible the gfm_tables: true option can be used to interpret only interior vertical bars as a table if a separation line is given, therefore

 Language|Rating
 --------|------
 Elixir  | awesome

is a table (if and only if gfm_tables: true) while

 Language|Rating
 Elixir  | awesome

never is.

HTML Blocks

HTML is not parsed recursively or detected in all conditions right now, though GFM compliance is a goal.

But for now the following holds:

A HTML Block defined by a tag starting a line and the same tag starting a different line is parsed as one HTML AST node, marked with %{verbatim: true}

E.g.

    iex(20)> lines = [ "<div><span>", "some</span><text>", "</div>more text" ]
    ...(20)> EarmarkParser.as_ast(lines)
    {:ok, [{"div", [], ["<span>", "some</span><text>"], %{verbatim: true}}, "more text"], []}

And a line starting with an opening tag and ending with the corresponding closing tag is parsed in similar fashion

    iex(21)> EarmarkParser.as_ast(["<span class=\"superspan\">spaniel</span>"])
    {:ok, [{"span", [{"class", "superspan"}], ["spaniel"], %{verbatim: true}}], []}

What is HTML?

We differ from strict GFM by allowing all tags not only HTML5 tags this holds for one liners....

    iex(22)> {:ok, ast, []} = EarmarkParser.as_ast(["<stupid />", "<not>better</not>"])
    ...(22)> ast
    [
      {"stupid", [], [], %{verbatim: true}},
      {"not", [], ["better"], %{verbatim: true}}]

and for multi line blocks

    iex(23)> {:ok, ast, []} = EarmarkParser.as_ast([ "<hello>", "world", "</hello>"])
    ...(23)> ast
    [{"hello", [], ["world"], %{verbatim: true}}]

HTML Comments

Are recognized if they start a line (after ws and are parsed until the next --> is found all text after the next '-->' is ignored

E.g.

    iex(24)> EarmarkParser.as_ast(" <!-- Comment\ncomment line\ncomment --> text -->\nafter")
    {:ok, [{:comment, [], [" Comment", "comment line", "comment "], %{comment: true}}, {"p", [], ["after"], %{}}], []}

Lists

Lists are pretty much GFM compliant, but some behaviors concerning the interpretation of the markdown inside a List Item's first paragraph seem not worth to be interpreted, examples are blockquote in a tight list item which we can only have in a loose one

Or a headline in a tight list item which, again is only available in the loose version in EarmarkParser.

furthermore this example demonstrates how weird and definitely not useful GFM's own interpretation can get.

Therefore we stick to a more predictable approach.

      iex(25)> markdown = [
      ...(25)> "* aa",
      ...(25)> "  ```",
      ...(25)> "Second",
      ...(25)> "  ```" ]
      ...(25)> as_ast(markdown)
      {:ok, [{"ul", [], [{"li", [], ["aa", {"pre", [], [{"code", [], ["Second"], %{}}], %{}}], %{}}], %{}}], []}

Also we do support the immediate style of block content inside lists

      iex(26)> as_ast("* > Nota Bene!")
      {:ok, [{"ul", [], [{"li", [], [{"blockquote", [], [{"p", [], ["Nota Bene!"], %{}}], %{}}], %{}}], %{}}], []}

or

      iex(27)> as_ast("1. # Breaking...")
      {:ok, [{"ol", [], [{"li", [], [{"h1", [], ["Breaking..."], %{}}], %{}}], %{}}], []}

Adding Attributes with the IAL extension

To block elements

HTML attributes can be added to any block-level element. We use the Kramdown syntax: add the line {: attrs } following the block.

    iex(28)> markdown = ["# Headline", "{:.from-next-line}"]
    ...(28)> as_ast(markdown)
    {:ok, [{"h1", [{"class", "from-next-line"}], ["Headline"], %{}}], []}

Headers can also have the IAL string at the end of the line

    iex(29)> markdown = ["# Headline{:.from-same-line}"]
    ...(29)> as_ast(markdown)
    {:ok, [{"h1", [{"class", "from-same-line"}], ["Headline"], %{}}], []}

A special use case is headers inside blockquotes which allow for some nifty styling in ex_doc* see this PR if you are interested in the technical details

    iex(30)> markdown = ["> # Headline{:.warning}"]
    ...(30)> as_ast(markdown)
    {:ok, [{"blockquote", [], [{"h1", [{"class", "warning"}], ["Headline"], %{}}], %{}}], []}

This also works for headers inside lists

    iex(31)> markdown = ["- # Headline{:.warning}"]
    ...(31)> as_ast(markdown)
    {:ok, [{"ul", [], [{"li", [], [{"h1", [{"class", "warning"}], ["Headline"], %{}}], %{}}], %{}}], []}

It still works for inline code, as it did before

    iex(32)> markdown = "`Enum.map`{:lang=elixir}"
    ...(32)> as_ast(markdown)
    {:ok, [{"p", [], [{"code", [{"class", "inline"}, {"lang", "elixir"}], ["Enum.map"], %{line: 1}}], %{}}], []}

attrs can be one or more of:

  • .className
  • #id
  • name=value, name="value", or name='value'

For example:

# Warning
{: .red}

Do not turn off the engine
if you are at altitude.
{: .boxed #warning spellcheck="true"}

To links or images

It is possible to add IAL attributes to generated links or images in the following format.

    iex(33)> markdown = "[link](url) {: .classy}"
    ...(33)> EarmarkParser.as_ast(markdown)
    { :ok, [{"p", [], [{"a", [{"class", "classy"}, {"href", "url"}], ["link"], %{}}], %{}}], []}

For both cases, malformed attributes are ignored and warnings are issued.

    iex(34)> [ "Some text", "{:hello}" ] |> Enum.join("\n") |> EarmarkParser.as_ast()
    {:error, [{"p", [], ["Some text"], %{}}], [{:warning, 2,"Illegal attributes [\"hello\"] ignored in IAL"}]}

It is possible to escape the IAL in both forms if necessary

    iex(35)> markdown = "[link](url)\\{: .classy}"
    ...(35)> EarmarkParser.as_ast(markdown)
    {:ok, [{"p", [], [{"a", [{"href", "url"}], ["link"], %{}}, "{: .classy}"], %{}}], []}

This of course is not necessary in code blocks or text lines containing an IAL-like string, as in the following example

    iex(36)> markdown = "hello {:world}"
    ...(36)> EarmarkParser.as_ast(markdown)
    {:ok, [{"p", [], ["hello {:world}"], %{}}], []}

Limitations

  • 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>
hello</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>

Annotations

N.B. this is an experimental feature from v1.4.16-pre on and might change or be removed again

The idea is that each markdown line can be annotated, as such annotations change the semantics of Markdown they have to be enabled with the annotations option.

If the annotations option is set to a string (only one string is supported right now, but a list might be implemented later on, hence the name), the last occurrence of that string in a line and all text following it will be added to the line as an annotation.

Depending on how that line will eventually be parsed, this annotation will be added to the meta map (the 4th element in an AST quadruple) with the key :annotation

In the current version the annotation will only be applied to verbatim HTML tags and paragraphs

Let us show some examples now:

Annotated Paragraphs

    iex(37)> as_ast("hello %> annotated", annotations: "%>")
    {:ok, [{"p", [], ["hello "], %{annotation: "%> annotated"}}], []}

If we annotate more than one line in a para the first annotation takes precedence

    iex(38)> as_ast("hello %> annotated\nworld %> discarded", annotations: "%>")
    {:ok, [{"p", [], ["hello \nworld "], %{annotation: "%> annotated"}}], []}

Annotated HTML elements

In one line

    iex(39)> as_ast("<span>One Line</span> // a span", annotations: "//")
    {:ok, [{"span", [], ["One Line"], %{annotation: "// a span", verbatim: true}}], []}

or block elements

    iex(40)> [
    ...(40)> "<div> : annotation",
    ...(40)> "  <span>text</span>",
    ...(40)> "</div> : discarded"
    ...(40)> ] |> as_ast(annotations: " : ")
    {:ok, [{"div", [], ["  <span>text</span>"], %{annotation: " : annotation", verbatim: true}}], []}

Commenting your Markdown

Although many markdown elements do not support annotations yet, they can be used to comment your markdown, w/o cluttering the generated AST with comments

    iex(41)> [
    ...(41)> "# Headline --> first line",
    ...(41)> "- item1 --> a list item",
    ...(41)> "- item2 --> another list item",
    ...(41)> "",
    ...(41)> "<http://somewhere/to/go> --> do not go there"
    ...(41)> ] |> as_ast(annotations: "-->")
    {:ok, [
      {"h1", [], ["Headline"], %{}},
      {"ul", [], [{"li", [], ["item1 "], %{}}, {"li", [], ["item2 "], %{}}], %{}},
      {"p", [], [{"a", [{"href", "http://somewhere/to/go"}], ["http://somewhere/to/go"], %{}}, " "], %{annotation: "--> do not go there"}}
      ], []
     }

EarmarkParser.as_ast/2

iex(42)> markdown = "My `code` is **best**"
...(42)> {:ok, ast, []} = EarmarkParser.as_ast(markdown)
...(42)> ast
[{"p", [], ["My ", {"code", [{"class", "inline"}], ["code"], %{line: 1}}, " is ", {"strong", [], ["best"], %{}}], %{}}]

    iex(43)> markdown = "```elixir\nIO.puts 42\n```"
    ...(43)> {:ok, ast, []} = EarmarkParser.as_ast(markdown, code_class_prefix: "lang-")
    ...(43)> ast
    [{"pre", [], [{"code", [{"class", "elixir lang-elixir"}], ["IO.puts 42"], %{}}], %{}}]

Rationale:

The AST is exposed in the spirit of Floki's.

EarmarkParser.version/0

Accesses current hex version of the EarmarkParser application. Convenience for iex usage.

Contributing

Pull Requests are happily accepted.

Please be aware of one caveat when correcting/improving README.md.

The README.md is generated by the coammand mix task xtra from README.md.eex and docstrings by means of %moduledoc or %functiondoc directives.

Please identify the origin of the generated text you want to correct and then apply your changes there.

Then issue the mix task readme, this is important to have a correctly updated README.md after the merge of your PR.

Thank you all who have already helped with Earmark/EarmarkParser, your names are duely noted in RELEASE.md.

Author

Copyright © 2014,5,6,7,8,9;2020 Dave Thomas, The Pragmatic Programmers @/+pragdave, dave@pragprog.com Copyright © 2020,1,2,3 Robert Dober robert.dober@gmail.com

LICENSE

Same as Elixir, which is Apache License v2.0. Please refer to LICENSE for details.

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