Rapid app development with Haskell - GovHack experience report

Learn what happened when three functional programming aficionadi
took on the GovHack open data competition armed with a Haskell compiler,
a handful of libraries and whole lot of hubris.

GovHack is an annual open data event in Australia. A coordinated
release of federal, state and local government data is celebrated
with a weekend-long hackfest, with prizes awarded for the most
interesting and useful apps, mashups or remixes.

Three hackers (including the presenter) who are passionate about
Haskell - a strongly typed, purely functional programming language -
decided to put their skills to the test and entered GovHack 2014 to
see what they could build in a weekend using Haskell.

Transcript

1. Rapid app development with Haskell A GovHack experience report Fraser Tweedale (@hackuador)
2. Introduction
3. About me Developer at Red Hat. FreeIPA identity management and Dogtag PKI. Mostly Python and Java at work. Mostly Haskell at home.
4. This talk Part experience report; part Haskell/functional programming advocacy; part open data advocacy. What is Haskell? Why Haskell? GovHack project implementation details; wins and pain points. Field guide to Haskell web technologies
5. The Haskell Programming Language Functional programming language Strong, static type system Pure (no side-effects) Lazy (only evaluates expressions if/when needed) Performance
6. Why Haskell? Type system prevents many kinds of programmer errors. Purity → referential transparency → equational reasoning Powerful, beautiful abstractions. Don’t repeat yourself! High-quality libraries and frameworks. Why Functional Programming Matters; Hughes 1984. http://www.cse.chalmers.se/~rjmh/Papers/whyfp.pdf
7. GovHack
8. GovHack Annual open data event in Australia; weekend hackfest. Competition; do cool/useful things with newly-released data sets; prizes! All levels of govt involved; awesome that they are doing this; get behind it! Brisbane Functional Programming Group entered a team (3 people)
9. GovHack - deciding the project Shortlisted a handful of datasets. Assessed data sanity, formats/syntax and usefulness. Considered writing libraries to parse/convert peculiar formats used in various data sets (unusual date formats, etc) Eventually decided on. . .
10. GovHack - Brisbane Park Finder Search council parks in Brisbane by location and facilities. “Find a park near Chermside with BBQs and dog off-leash area” View map of park and surrounds including boundary with facilities marked on map with icons. http://brisparks.info/ UX sucks; enter if you dare! https://github.com/bfpg/brisparks.info
11. GovHack - Brisbane Park Finder
12. GovHack - Brisbane Park Finder
13. Implementation
14. Implementation - importing data Most datasets were CSV. cassava library for parsing CSVs into custom data types. Elegant and type-safe.
15. Implementation - importing data Data type representing a park facility CSV record: data Facility = Facility { _facParkNumber :: Int , _facParkName :: Text , _nodeId :: Int , _nodeUse :: Text , _nodeName :: Text , _description :: Text , _easting :: Double , _northing :: Double }
16. Implementation - importing data cassava; CSV parser instance for Facility data type: instance FromNamedRecord Facility where parseNamedRecord m = Facility <$> m .: "PR_NO" <*> m .: "PARK_NAME" <*> m .: "NODE_ID" <*> m .: "NODE_USE" <*> m .: "NODES_NAME" <*> m .: "DESCRIPTION" <*> m .: "EASTING" <*> m .: "NORTHING"
17. Implementation - importing data cassava; import facilities from CSV: importFacilities :: Postgres -> IO () importFacilities db = do fileContents <- readFile "facilities.csv" case decodeByName fileContents of Left err -> putStrLn ("CSV parse error: " ++ err) Right facilities -> runWithDb (mapM_ insertFacility facilities) db
18. Implementation - database postgresql-simple library; reading DB records: instance FromRow Facility where fromRow = Facility <$> field <*> field <*> field <*> field <*> field <*> field <*> field <*> field
19. Implementation - database postgresql-simple library; writing DB records: instance ToRow Facility where toRow f = [ toField (f ^. facParkNumber) , toField (f ^. facParkName) , toField (f ^. nodeId) , toField (f ^. nodeUse) , toField (f ^. nodeName) , toField (f ^. description) , toField (f ^. easting) , toField (f ^. northing) ]
20. Implementation - database postgresql-simple library; select facilities by park number: getFacilities :: Int -> Db [Facility] getFacilities id = query [sql| SELECT park_number, park_name, node_id, node_use, node_name, description, easting, northing FROM park_facility f WHERE f.park_number = ? |] (Only id) -- a single ? param
21. Implementation - Snap Framework Haskell web framework Fast web server Snaplets to extend framework functionality templating, authentication, session management, DB etc. Scaffolding for quick setup
22. Implementation - heist templating heist; Snap templating system. Interpolation: <div class="park" data-number="${parkNumber}"> <h4><parkName/></h4> <p>Located on <parkStreet/>, in <parkSuburb/>.</p> Some sanity checks at load time. mismatched tags; </p> found inside <div> tag I wish these were compile errors!
23. Implementation - JavaScript PureScript is a pure, strongly-typed Alt-JS. Similar syntax to Haskell; similar expressiveness. FFI for safe interaction with impure JavaScript environment. In keeping with strongly-typed FP theme, decided to do the front-end in PureScript. One small problem. . . Noone actually knew PureScript Eventually abandoned for raw JavaScript.
24. Retrospective “Haskell just got out of the way; pain points were other things.” “You can make changes at 3am; as long as the code is compiling you can come back and not be too afraid.” Loss of type safety at database interface bit us a few times. PureScript: don’t try to learn conceptually dense things during a hackfest. UX sucked; we needed someone with UX focus. Great fun. Would Haskell again. Bring on GovHack 2015.
25. Field guide to Haskell web technologies
26. Servers WAI - Web Application Interface à la Rack, WSGI et al. Application, Middleware, Request, Response APIs Used by several (not all) frameworks Warp (HTTP server) The premier WAI handler Fast
27. How fast is Warp? http://www.aosabook.org/en/posa/warp.html
28. Frameworks Yesod Type-safe routes, URLs, templates. Scaffolding http://www.yesodweb.com/ Scotty Microframework à la Sinatra. https://github.com/scotty-web/scotty HappStack http://happstack.com/docs/crashcourse/index.html Silk rest Define REST APIs; generate client libs; auto docs Runs on Snap, HappStack or native WAI https://silkapp.github.io/rest/
29. Deploying Haskell apps Platform as a Service (PaaS) OpenShift community cartridge Heroku buildpack FP Application Server (https://www.fpcomplete.com/) http://www.haskell.org/haskellwiki/Web/Cloud Lightning talk: http://is.gd/CNx0na Docker Haskell/GHC images: https://registry.hub.docker.com/ No official Language Stack for Haskell yet. DIY
30. Summary Open data is important, and fun! You have useful skills, so get involved. You might win $$$ Functional programming matters. Lots of lessons learned in taking on GovHack in Haskell. Haskell is great for rapid (web) app development. FP + types + good libraries/frameworks = powerful combo. Deployment options still a bit immature. Don’t neglect UX!
31. Resources Learn Haskell: https://github.com/bitemyapp/learnhaskell Snap Quick Start Guide: http://snapframework.com/docs/quickstart PureScript by Example: https://leanpub.com/purescript/ HaskellWiki: http://www.haskell.org/haskellwiki/Web GovHack: http://www.govhack.org/ BFPG: http://bfpg.org ; #bfpg (Freenode)
32. Thanks for listening Copyright 2014 Fraser Tweedale This work is licensed under the Creative Commons Attribution 4.0 International License. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/. Slides https://github.com/frasertweedale/talks/ Email frase@frase.id.au Twitter @hackuador
33. Questions