What is this?
=============
 
This is an implementation of John Gruber's "markdown"
(http://daringfireball.net/projects/markdown/) in C.
It uses a PEG grammar to define the syntax. This should allow easy
modification and extension.
 
It is pretty fast. A 179K text file that takes 5.7 seconds for
Markdown.pl (v. 1.0.1) to parse takes only 0.2 seconds for this
markdown.  It does, however, use a fair amount of memory.
 
Installing
==========
 
This program is written in portable ANSI C. For convenience, two
required dependencies are included in the source directory:
 
  * bsittler's my_getopt option parsing library
    (http://www.geocities.com/bsittler/)
 
  * Ian Piumarta's peg/leg PEG parser generator
    (http://piumarta.com/software/peg/)
 
These will be built automatically.
 
To make the 'markdown' executable:
 
    make
 
Then, for usage instructions:
 
    ./markdown -h
 
To run John Gruber's Markdown 1.0.3 test suite:
 
    make test
 
The test suite will fail on one of the list tests.  Here's why.
Markdown.pl encloses "item one" in the following list in `<p>` tags:
 
    1.  item one
        * subitem
        * subitem
    
    2.  item two
 
    3.  item three
 
peg-markdown does not enclose "item one" in <p> tags unless it has a
following blank line. This is consistent with the official markdown
syntax description, and lets the author of the document choose whether
`<p>` tags are desired.
 
Extensions
==========
 
peg-markdown supports extensions to standard markdown syntax.
These can be turned on using the command line flag `-x`.  `-x`
by itself turns on all extensions; to turn on extensions selectively,
specify their names after `-x`, for example: `-xsmart`.
 
The `smart` extension provides "smart quotes", dashes, and ellipses.
 
The `notes` extension provides a footnote syntax like that of
Pandoc or PHP Markdown Extra.
 
Hacking
=======
 
It should be pretty easy to modify the program to produce other formats
than HTML or LaTeX, and to parse syntax extensions.  A quick guide:
 
  * `markdown_peg.h` contains declarations for both `markdown_parser.leg`
    and `markdown_output.c`.
 
  * `markdown_parser.leg` contains the grammar itself, the `markdown()`
    function, and some utility functions used by the parser actions.
 
  * `markdown_output.c` contains functions for printing the `Element`
    structure in various output formats.  (This includes calling
    `markdown()` again when needed to parse list items and blockquotes,
    which are stored initially as raw strings.)
 
  * To add an output format, add the format to `formats`, modify
    `print_element`, and add functions `print_XXXX_string`,
    `print_XXXX_element`, and `print_XXXX_element_list`. Also add an
    option in the main program that selects the new format. Don't forget
    to add it to the help message.
 
  * To add syntax extensions, define them in the PEG grammar (bottom part
    of `markdown_parser.leg`), using existing extensions as a guide.
    New inline elements will need to be added to `Inline =`; new block
    elements will need to be added to `Block =`. If you need to add new
    types of elements (e.g. `FOOTNOTE`), modify the `keys` enum. By using
    `&{ }` rules one can selectively disable extensions depending
    on command-line options. For example, `&{ extension(EXT_SMART) }`
    succeeds only if the `EXT_SMART` bit of the global
    `syntax_extensions` is set.  Add your option to `markdown_extensions`,
    and modify the option parsing in `markdown.c` so that your option gets
    set appropriately.
 
  * Note:  Avoid using `[^abc]` character classes in the grammar, because they
    cause problems with non-ascii input.  Instead, use:  `( !'a' !'b' !'c' . )`