add README.markdown, rm README.peg-markdown
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Michael Teichgräber
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README.markdown
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README.markdown
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This is an implementation of John Gruber's [markdown][] in
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[Go][]. It is a translation of [peg-markdown][], written by
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John MacFarlane in C, into Go. It is using a modified version
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of Andrew J Snodgrass' PEG parser [peg][] -- now supporting
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LEG grammars --, which is itself based on the parser used
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by peg-markdown.
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[markdown]: http://daringfireball.net/projects/markdown/
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[peg-markdown]: https://github.com/jgm/peg-markdown
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[peg]: https://github.com/pointlander/peg
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[Go]: http://golang.org/
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Support for HTML output is implemented, but Groff and LaTeX
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output have not been ported. The output should be identical
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to that of peg-markdown.
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The Go version is around 5x slower than the original C
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version. A marked speed improvement has been achieved by
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converting function `preformat` from concatenating strings
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to using bytes.Buffer. At other places, where this kind of
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modification had been tried, performance did not improve. Also,
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pre-allocating a large buffer for `element`s didn't show a
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significant difference from allocating `element`s one at a time.
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## Installation
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Provided you have a recent copy of Go, and git is available,
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goinstall github.com/knieriem/markdown
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should install the package into
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`$GOROOT/src/pkg/github.com/knieriem/markdown`, and build
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it. During the build, a copy of [knieriem/peg][] will be
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downloaded from github and compiled (`make peg` if done
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manually).
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**NOTE:** At the moment, goinstall most likely will fail,
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as it does not use the package's Makefile, but generates
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its own, which is not sufficient as it does not know how
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to build parser.leg.go from parser.leg. As a workaround,
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after the failed goinstall, please do the following steps to
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finish the installation:
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cd $GOROOT/src/pkg/github.com/knieriem/markdown
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gomake install
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See doc.go for an example how to use the package.
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To create the command line program *markdown,* run
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cd $GOROOT/src/pkg/github.com/knieriem/markdown
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gomake cmd
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the binary should then be available in subdirectory *cmd.*
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To run the Markdown 1.0.3 test suite, type
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make mdtest
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This will download peg-markdown, in case you have `git`
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available, build cmd/markdown, and run the test suite.
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The test suite will fail on one test, for the same reason which
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applies to peg-markdown, because the grammar is the same.
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See the [original README][] for details.
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[original README]: https://github.com/jgm/peg-markdown/blob/master/README.markdown
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[knieriem/peg]: https://github.com/knieriem/peg
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## Known issues
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Emphasis and strong markup within items of lists, as in input
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like ./PHP Markdown Extra.mdtest/Emphasis.text from Michel
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Fortin's [MDTest][] package,
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1. ***test test***
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2. ___test test___
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3. *test **test***
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4. **test *test***
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...
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seem to present a problem for the LEG parser, which needs
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(on my system) around four minutes to process that file.
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[MDTest]: http://git.michelf.com/mdtest/
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## Todo
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* Implement definition lists (work in progress), and perhaps tables
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* Rename element key identifiers, so that they are not public
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* Where appropriate, use more idiomatic Go code
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## Subdirectory Index
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* peg – PEG parser generator (modified) from Andrew J Snodgrass
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* peg/leg – LEG parser generator, based on PEG
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* cmd – command line program `markdown`
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@ -1,214 +0,0 @@
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What is this?
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=============
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This is an implementation of John Gruber's [markdown][] in C. It uses a
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[parsing expression grammar (PEG)][] to define the syntax. This should
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allow easy modification and extension. It currently supports output in
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HTML, LaTeX, or groff_mm formats, and adding new formats is relatively
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easy.
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[parsing expression grammar (PEG)]: http://en.wikipedia.org/wiki/Parsing_expression_grammar
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[markdown]: http://daringfireball.net/projects/markdown/
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It is pretty fast. A 179K text file that takes 5.7 seconds for
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Markdown.pl (v. 1.0.1) to parse takes less than 0.2 seconds for this
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markdown. It does, however, use a lot of memory (up to 4M of heap space
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while parsing the 179K file, and up to 80K for a 4K file). (Note that
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the memory leaks in earlier versions of this program have now been
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plugged.)
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Both a library and a standalone program are provided.
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peg-markdown is written and maintained by John MacFarlane (jgm on
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github), with significant contributions by Ryan Tomayko (rtomayko).
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It is released under both the GPL and the MIT license; see LICENSE for
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details.
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Installing
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==========
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On a linux or unix-based system
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-------------------------------
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This program is written in portable ANSI C. It requires
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[glib2](http://www.gtk.org/download.html). Most *nix systems will have
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this installed already. The build system requires GNU make.
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The other required dependency, [Ian Piumarta's peg/leg PEG parser
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generator](http://piumarta.com/software/peg/), is included in the source
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directory. It will be built automatically. (However, it is not as portable
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as peg-markdown itself, and seems to require gcc.)
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To make the 'markdown' executable:
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make
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(Or, on some systems, `gmake`.) Then, for usage instructions:
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./markdown --help
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To run John Gruber's Markdown 1.0.3 test suite:
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make test
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The test suite will fail on one of the list tests. Here's why.
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Markdown.pl encloses "item one" in the following list in `<p>` tags:
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1. item one
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* subitem
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* subitem
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2. item two
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3. item three
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peg-markdown does not enclose "item one" in `<p>` tags unless it has a
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following blank line. This is consistent with the official markdown
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syntax description, and lets the author of the document choose whether
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`<p>` tags are desired.
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Cross-compiling for Windows with MinGW on a linux box
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-----------------------------------------------------
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Prerequisites:
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* Linux system with MinGW cross compiler For Ubuntu:
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sudo apt-get install mingw32
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* [Windows glib-2.0 binary & development files](http://www.gtk.org/download-windows.html).
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Unzip files into cross-compiler directory tree (e.g., `/usr/i586-mingw32msvc`).
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Steps:
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1. Create the markdown parser using Linux-compiled `leg` from peg-0.1.4:
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./peg-0.1.4/leg markdown_parser.leg >markdown_parser.c
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(Note: The same thing could be accomplished by cross-compiling leg,
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executing it on Windows, and copying the resulting C file to the Linux
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cross-compiler host.)
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2. Run the cross compiler with include flag for the Windows glib-2.0 headers:
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for example,
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/usr/bin/i586-mingw32msvc-cc -c \
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-I/usr/i586-mingw32msvc/include/glib-2.0 \
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-I/usr/i586-mingw32msvc/lib/glib-2.0/include -Wall -O3 -ansi markdown*.c
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3. Link against Windows glib-2.0 headers: for example,
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/usr/bin/i586-mingw32msvc-cc markdown*.o \
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-Wl,-L/usr/i586-mingw32msvc/lib/glib,--dy,--warn-unresolved-symbols,-lglib-2.0 \
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-o markdown.exe
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The resulting executable depends on the glib dll file, so be sure to
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load the glib binary on the Windows host.
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Compiling with MinGW on Windows
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-------------------------------
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These directions assume that MinGW is installed in `c:\MinGW` and glib-2.0
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is installed in the MinGW directory hierarchy (with the mingw bin directory
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in the system path).
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Unzip peg-markdown in a temp directory. From the directory with the
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peg-markdown source, execute:
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cd peg-0.1.4
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for %i in (*.c) do @gcc -g -Wall -O3 -DNDEBUG -c -o %~ni.o %i
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gcc -o leg.exe leg.o tree.o compile.o
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cd ..
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peg-0.1.4\leg.exe markdown_parser.leg >markdown_parser.c
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@for %i in (markdown*.c) do @gcc -mms-bitfields -Ic:/MinGW/include/glib-2.0 -Ic:/MinGW/lib/glib-2.0/include -c -o %~ni.o %i
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gcc -O3 -Lc:/MinGW/lib/glib-2.0 -lglib-2.0 -lintl markdown.o markdown_lib.o markdown_output.o markdown_parser.o -o markdown.exe -Wl,--dy,--warn-unresolved-symbols,-lglib-2.0,-Lc:/MinGW/lib/glib-2.0,-lglib-2.0,-lintl
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(Windows instructions courtesy of Matt Wolf.)
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Extensions
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==========
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peg-markdown supports extensions to standard markdown syntax.
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These can be turned on using the command line flag `-x` or
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`--extensions`. `-x` by itself turns on all extensions. Extensions
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can also be turned on selectively, using individual command-line
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options. To see the available extensions:
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./markdown --help-extensions
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The `--smart` extension provides "smart quotes", dashes, and ellipses.
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The `--notes` extension provides a footnote syntax like that of
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Pandoc or PHP Markdown Extra.
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Using the library
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=================
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The library exports two functions:
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GString * markdown_to_g_string(char *text, int extensions, int output_format);
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char * markdown_to_string(char *text, int extensions, int output_format);
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The only difference between these is that `markdown_to_g_string` returns a
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`GString` (glib's automatically resizable string), while `markdown_to_string`
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returns a regular character pointer. The memory allocated for these must be
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freed by the calling program, using `g_string_free()` or `free()`.
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`text` is the markdown-formatted text to be converted. Note that tabs will
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be converted to spaces, using a four-space tab stop. Character encodings are
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ignored.
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`extensions` is a bit-field specifying which syntax extensions should be used.
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If `extensions` is 0, no extensions will be used. If it is `0xFFFFFF`,
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all extensions will be used. To set extensions selectively, use the
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bitwise `&` operator and the following constants:
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- `EXT_SMART` turns on smart quotes, dashes, and ellipses.
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- `EXT_NOTES` turns on footnote syntax. [Pandoc's footnote syntax][] is used here.
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- `EXT_FILTER_HTML` filters out raw HTML (except for styles).
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- `EXT_FILTER_STYLES` filters out styles in HTML.
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[Pandoc's footnote syntax]: http://johnmacfarlane.net/pandoc/README.html#footnotes
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`output_format` is either `HTML_FORMAT`, `LATEX_FORMAT`, or `GROFF_MM_FORMAT`.
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To use the library, include `markdown_lib.h`. See `markdown.c` for an example.
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Hacking
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=======
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It should be pretty easy to modify the program to produce other formats
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than HTML or LaTeX, and to parse syntax extensions. A quick guide:
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* `markdown_parser.leg` contains the grammar itself.
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* `markdown_output.c` contains functions for printing the `Element`
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structure in various output formats.
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* To add an output format, add the format to `markdown_formats` in
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`markdown_lib.h`. Then modify `print_element` in `markdown_output.c`,
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and add functions `print_XXXX_string`, `print_XXXX_element`, and
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`print_XXXX_element_list`. Also add an option in the main program
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that selects the new format. Don't forget to add it to the list of
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formats in the usage message.
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* To add syntax extensions, define them in the PEG grammar
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(`markdown_parser.leg`), using existing extensions as a guide. New
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inline elements will need to be added to `Inline =`; new block
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elements will need to be added to `Block =`. (Note: the order
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of the alternatives does matter in PEG grammars.)
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* If you need to add new types of elements, modify the `keys`
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enum in `markdown_peg.h`.
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* By using `&{ }` rules one can selectively disable extensions
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depending on command-line options. For example,
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`&{ extension(EXT_SMART) }` succeeds only if the `EXT_SMART` bit
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of the global `syntax_extensions` is set. Add your option to
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`markdown_extensions` in `markdown_lib.h`, and add an option in
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`markdown.c` to turn on your extension.
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* Note: Avoid using `[^abc]` character classes in the grammar, because
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they cause problems with non-ascii input. Instead, use: `( !'a' !'b'
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!'c' . )`
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