126 lines
4.0 KiB
Markdown
126 lines
4.0 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 itself is 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 and groff mm output is implemented, but LaTeX
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output has not been ported. The output is identical
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to that of peg-markdown.
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I try to keep the grammar in sync with the C version, by
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cherry-picking relevant changes. In the commit history the
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corresponding revisions have a suffix *[jgm/peg-markdown].*
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A simple benchmark has been done by comparing the
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execution times of the Go binary (cmd/main.go) and the
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original C implementation's binary needed for processing
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a Markdown document, which had been created by
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concatenating ten [Markdown syntax descriptions][syntax].
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[syntax]: http://daringfireball.net/projects/markdown/syntax.text
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The C version is still around 1.3x faster than the Go version.
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## Installation
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Provided you have a copy of Go 1, and git is available,
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go get github.com/knieriem/markdown
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should download and install the package according to
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your GOPATH settings.
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See doc.go for an example how to use the package. There has
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been an API change recently: Where you previously wrote
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buf, err := ioutil.ReadAll(os.Stdin)
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...
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doc := markdown.Parse(string(buf), markdown.Extensions{Smart: true})
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doc.WriteHtml(w)
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you would now write:
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p := markdown.NewParser(&markdown.Extensions{Smart: true})
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w := bufio.NewWriter(os.Stdout)
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p.Markdown(os.Stdin, markdown.ToHTML(w))
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w.Flush()
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One purpose of the change is to have a Parser that can be
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reused between invocations of the converter.
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---
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To create the command line program *markdown,* run
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go build github.com/knieriem/markdown/cmd/markdown
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the binary should then be available in the current directory.
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To run tests, type
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go test github.com/knieriem/markdown
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At the moment, tests are based on the .text files from the
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Markdown 1.0.3 test suite created by John Gruber, [imported from
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peg-markdown][testsuite]. The output of the conversion of these
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.text files to html is compared to the output of peg-markdown.
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[testsuite]: https://github.com/jgm/peg-markdown/tree/master/MarkdownTest_1.0.3
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## Development
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There is not yet a way to create a Go source file like
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`parser.leg.go` automatically from another file, `parser.leg`,
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when building packages and commands using the Go tool. To make
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*markdown* installable using `go get`, `parser.leg.go` has
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been added to the VCS.
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`Make parser` will update `parser.leg.go` using `leg` – which
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is part of [knieriem/peg][] at github –, if parser.leg has
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been changed, or if the Go file is missing. If a copy of *peg*
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is not yet present on your system, run
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go get github.com/knieriem/peg
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Then `make parser` should succeed.
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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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* Port tables and perhaps other extensions from [fletcher/peg-multimarkdown][mmd].
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## Subdirectory Index
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* cmd/markdown – command line program `markdown`
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[mmd]: https://github.com/fletcher/peg-multimarkdown
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