Exposing the guts of Pandoc, the marvelous Haskell-driven document conversion tool.

1. Pandoc:
The Deep Dive
All that is great
stands in the storm

2. ● Universal markup converter == " the swiss
army knife of text markup formats"
● ALL HASKELL
● Example:
pandoc -o myDoc.md myDoc.html
pandoc -f html -t latex hackage.org
pandoc myDoc.txt -o myDoc.pdf
What is Pandoc?

3. ● Reads:
○ Markdown (GitHub, Strict, etc.), HTML, LaTeX,
Textile, reStructuredText, JSON,
● Writes:
○ Markdown, reStructuredText, HTML, Docbook
XML, OpenDocument XML, ODT, RTF, groff
man, MediaWiki markup, GNU Texinfo, LaTeX,
ConTeXt, EPUB, Textile, Emacs org-mode, Slidy,
S5
● Extensions for LaTeX math, tables, etc.
● Note to self: Pandoc in the CLI
What is Pandoc? (pt. 2)

4. ● Performance vis-à-vis scripting languages
● Type safety
● Text.Parsec library
● Hypermuscular list processing (more
about FP more generally than about
Haskell)
Why Haskell?

5. ● One possibility: functions devoted to each
type-to-type combination
○ markdownToHTML
○ HTMLtoEPUB
○ 12^31 possibilities
○ FUCK THAT
● Vastly better possibility?
Reader -->
Neutral Haskell data type -->
Writer -->
Converted document
Possible approaches

6. ● Semi-stateful, non-opinionated REGEX
machine
○ Accumulative — return (x:xs)
○ getParserState
○ modifyState
● Core functions
○ parse
■ parse parser filePath input
■ parse numbers "" "a,b,2,3"
○ many
○ skipMany
○ manyAccum
● type Parser t s = Parsec t s
Text.Parsec

7. ● Neutral data types
○ Pandoc = [Block]
○ Block = [(Inline || Block)]
○ Inline
○ etc.
● Reader
○ Applies parsers to documents
○ Documents are treated as lists
● Writer
○ Converts neutral data type into document
○ Again, documents are just structured lists
Basic flow

8. ● Readers/Markdown.hs
● Writers/HTML.hs
● Pandoc/Builder.hs
Markdown to HTML

9. ● When doing big, complex things with FP,
you're probably going to end up thinking in
terms of lists
● Lists are infinitely flexible
● Hard to escape state entirely
○ ReaderState
○ WriterState
● Don't give up
● Force yourself to give a presentation at
PDXFunc
General lessons