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A Haskell implementation of markdown using a PEG grammar
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Markdown.hs - an implementation of markdown in Haskell, using a PEG grammar. (c) 2008 John MacFarlane, released under the GPL. Markdown is a plain-text syntax for writing HTML (and potentially other formats), by John Gruber (<http://daringfireball.net/projects/markdown/>). To build (using the GHC Haskell compiler): ghc -O2 --make Markdown.hs or just: make Markdown.hs uses John Meacham's Frisby PEG parsing library. This can be found at <http://repetae.net/computer/frisby>, but for convenience the required files are included in this directory. The XML formatting library from Pandoc (<http://johnmacfarlane.net/pandoc>). is also included for convenience. This is a first draft. I'm sure there are many ways in which it can be improved. Currently it passes the Markdown 1.0.3 test suite, with the exception of two small corner cases. The grammar definition is the function 'doc' in Markdown.hs. It should be easy to change and extend it. If you want to add new block or inline elements, you'll also need to modify the definitions of 'Block' and 'Inline', and add clauses to handle these to 'inlineToHtml' and 'blockToHtml'. There are a couple of features of markdown that cannot be handled straightforwardly in a PEG grammar; workarounds have been provided here. The first is the syntax for code spans: text enclosed by equal-sized sequences of backticks. I have simulated this by including separate rules for sequences of backticks of length 1 to 10, but this doesn't precisely capture the markdown rule. The second is the syntax for indented blocks, e.g. in block quotes and lists. I have handled these by having the parser return unparsed markdown text for the block contents; the parser is then called again by the function 'blockToHtml'. See LICENSE for license information for Markdown.hs and the other included files.