retroforth/example/markdown.retro

# Markdown to HTML

RETRO's source files generally use a subset of Markdown for
formatting. This is a small tool to convert this into HTML.

## Features

Recognizes:

- lists
- indented code blocks
- paragraphs
- headers
- fenced code blocks
- horizontal rules
- *inline* _formatting_ elements

## Limitations

This only supports a limited subset of full Markdown. I am
not adding support for the various linking formats, ordered
lists, underlined headers, doubled asterisk, doubled
underscores, multiple line/paragraph list entries, or images.

The CSS used is extracted from the end of this file. I only
do a tiny bit of styling by default; just enough to ensure
that code blocks are easily identified.

----

## The Code

Begin by locating and extracting the CSS.

~~~
'<style> s:put nl
FALSE sys:name [ over [ '##_CSS s:eq? or ] -if; s:put nl ] file:for-each-line
drop
'</style> s:put nl
~~~

The first couple of words are a variation of `s:put` that
generates HTML codes for specific characters. This ensures
that code output displays correctly.

~~~
:c:put<code>
  $< [ '&lt; s:put ] case
  $> [ '&gt; s:put ] case
  $& [ '&amp; s:put ] case
  ASCII:SPACE [ '&nbsp; s:put ] case
  c:put ;

:s:put<code> [ c:put<code> ] s:for-each ;
~~~

For regular text, there are a couple of inline formatting things
to deal with.

~~~
'Emphasis var
'Strong var
'Escape var
'Code var

:format
  @Escape [ &Escape v:on ] if;
  $` [ @Escape [ &Escape v:off $* c:put ] if;
       @Code n:zero? [ '<tt_style='display:inline'> &Code v:on ]
                     [ '</tt> &Code v:off ] choose s:put ] case
  $* [ @Escape @Code or [ &Escape v:off $* c:put ] if;
       @Strong n:zero? [ '<strong> &Strong v:on ]
                       [ '</strong> &Strong v:off ] choose s:put ] case
  $_ [ @Escape @Code or [ &Escape v:off $_ c:put ] if;
       @Emphasis n:zero? [ '<em> &Emphasis v:on ]
                         [ '</em> &Emphasis v:off ] choose s:put ] case
  c:put ;

:s:put<formatted> [ format ] s:for-each ;
~~~

Next, handling of code blocks.

The fences need to start and end with `~~~` on a line by
itself. (This will also handle test blocks using three
bacticks as well)

~~~
'Block var
:in-block? @Block ;
:block?    dup [ '~~~ s:eq? ] [ '``` s:eq? ] bi or ;
:toggle    drop @Block n:zero? !Block ;
:format:block  '<tt> s:put s:put<code> '</tt> s:put nl ; 
~~~

After this, I define detection and formatting of headers. The
headers should look like:

    # Level 1
    ## Level 2
    ### Level 3

~~~
:header?
  dup [ '# s:begins-with?   ]
      [ '## s:begins-with?  ]
      [ '### s:begins-with? ] tri or or ;

:format:head
  ASCII:SPACE s:split
  '#   [ '<h1> s:put n:inc s:put '</h1> s:put nl ] s:case
  '##  [ '<h2> s:put n:inc s:put '</h2> s:put nl ] s:case
  '### [ '<h3> s:put n:inc s:put '</h3> s:put nl ] s:case
  drop ;
~~~

Indented code blocks are lines indented by four spaces.

~~~
:code? dup '____ s:begins-with? ;
:format:code '<tt> s:put #4 + s:put<code> '</tt> s:put nl ;
~~~

Horizonal rules consist of four or more - characters on
a line. E.g.,

    ----
    --------

~~~
:rule? dup '---- s:begins-with? ;
:format:rule drop '<hr> s:put nl ;
~~~

Lists start with a `-` or `*`, followed by a space, then
the item text.

~~~
:list? dup [ '-_ s:begins-with? ] [ '*_ s:begins-with? ] bi or ;
:format:list '<li> s:put #2 + s:put<formatted> '</li> s:put nl ;
~~~

Blank lines denote paragraph breaks.

~~~
:blank? dup s:length n:zero? ;
~~~

~~~
:format
  block? [ toggle ] if;
  in-block? [ format:block ] if;
  blank?  [ drop '<p> s:put nl ] if;
  header? [ format:head ] if;
  code?   [ format:code ] if;
  list?   [ format:list ] if;
  rule?   [ format:rule ] if;
  s:put<formatted> nl ;

#0 sys:argv [ format ] file:for-each-line
~~~

This concludes the Markdown (subset) in RETRO utility.

## CSS

    tt, pre {
      background: #eee;
      color: #111;
      font-family: monospace;
      white-space: pre;
      display: block;
      width: 100%;
    }