115 lines
3.9 KiB
Markdown
115 lines
3.9 KiB
Markdown
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.
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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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## Development
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[`Goinstall`][Goinstall] is creating its own Makefiles to build
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packages, based on the `.go` files found in the directory.
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It would not know about `parser.leg.go`, which had to be built
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by `leg` from the `parser.leg` grammar source file first.
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Because of this, to make *markdown* installable using
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`goinstall`, `parser.leg.go` has been added to the VCS.
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`Make` will update `parser.leg.go` using `leg`, which is part of
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[knieriem/peg][] at github, if parser.leg has been changed. If
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a copy of this package has not yet been downloaded -- i.e. no
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directory `./peg` is present --, `make` will perform the
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neccessary steps automatically (run `make peg` to manually
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download [knieriem/peg][]).
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To update [knieriem/peg][] run `gomake update-peg`. This will
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fetch available revisions from github, and remove the old
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*leg* binary.
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[goinstall]: http://golang.org/cmd/goinstall/
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[knieriem/peg]: https://github.com/knieriem/peg
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## Extensions
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In addition to the extensions already present in peg-markdown,
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this package also supports definition lists (option `-dlists`)
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similar to the way they are described in the documentation of
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[PHP Markdown Extra][].
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Definitions (`<dd>...</dd>`) are implemented using [`ListTight`][ListTight]
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and `ListLoose`, on which bullet lists and ordered lists are based
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already. If there is an empty line between the definition title and
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the first definition, a loose list is expected, a tight list otherwise.
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As definition item markers both `:` and `~` can be used.
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[PHP Markdown Extra]: http://michelf.com/projects/php-markdown/extra/#def-list
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[ListTight]: https://github.com/knieriem/markdown/blob/master/parser.leg#L191
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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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