production haskell

Reid Draper @reiddraper

wrangling the internet of things with haskell

production haskell

Reid Draper @reiddraper

production haskell today

production haskell at helium12 months in

lowest defect rate

easiest to refactorlowest defect rate

OSS libraries for everything*most enjoyable

easiest to refactorlowest defect rate

20k LOC

5 developers20k LOC

6 production services5 developers

20k LOC

build deploy monitor test develop

build deploy monitor test develop

cabal hell

cabal hell

stackhaskellstack.org

project specificsnapshot

ghc packages

2 seconds20k LOC

ordealgithub.com/reiddraper/ordeal

stack build self-contained

executable

build deploy monitor test develop

app!"" assets#   !"" images#   #   %"" favicon.ico#   !"" javascript#   #   %"" site.js#   %"" stylesheet#   %"" site.css%"" bin %"" app

restart appln -s app-370b347 currenttar -xzf app-370b347.tgz

restart appln -s app-83181ad current

60MB

build deploy monitor test develop

ekg

stdout file syslog

build deploy monitor test develop

QuickCheck

propEvent :: Event -> BoolpropEvent a = Just a == decode (encode a)

Event roundtrips in JSON: FAIL (0.04s) *** Failed! Falsifiable (after 1 test): Event {_severity = Error, _facility = Unspecified, _sampled = 1894-02-22 00:00:04.5986 UTC, _eventDetails = ElementDisconnect {_elementMAC = 8ec52584b2c82424}, _eventMessage = Nothing, _originator = http://www.ietf.org/rfc/rfc2396.txt, _reference = Just http://www.ietf.org/rfc/rfc2396.txt }

Event roundtrips in JSON: FAIL (0.04s) *** Failed! Falsifiable (after 1 test): Event {_severity = Error, _facility = Unspecified, _sampled = 1894-02-22 00:00:04.5986 UTC, _eventDetails = ElementDisconnect {_elementMAC = 8ec52584b2c82424}, _eventMessage = Nothing, _originator = http://www.ietf.org/rfc/rfc2396.txt, _reference = Just http://www.ietf.org/rfc/rfc2396.txt }

ghci> t1894-02-22 00:00:04.5986 UTCghci> Data.Aeson.encode t"\"1894-02-22T00:00:04.598Z\""

build deploy monitor test develop

postgresql-transactionalgithub.com/helium/postgresql-transactional

lookupUser emailAddress = queryFirst [emailAddress] [sql| SELECT id, email, name, timezone FROM user_account WHERE email = ? |]

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BEGINBEGINCOMMITCOMMIT

BEGINBEGINCOMMITCOMMIT

BEGINBEGINCOMMITCOMMIT

WARNING:  there is already a transaction in progressWARNING:  there is no transaction in progress

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lookupUser :: Connection -> Text -> IO (Maybe User)lookupUser connection emailAddress = queryFirst [emailAddress] [sql| SELECT id, email, name, timezone FROM user_account WHERE email = ? |] connection

createUser :: Connection -> NewUser -> IO User

createOrganization :: Connection -> NewOrganization -> IO Organization

addUserToOrganization :: Connection -> User -> Organization -> IO ()

createUserAndOrganization :: Connection -> NewUser -> IO ()createUserAndOrganization connection newUser = withTransaction connection $ do let newOrganization = NewOrganization (newUser ^. name) user <- createUser connection newUser org <- createOrganization connection newOrganization addUserToOrganization connection user org

-- NOTE: you MUST wrap this in a transaction!!createUserAndOrganization :: Connection -> NewUser -> IO ()createUserAndOrganization connection newUser = do let newOrganization = NewOrganization (newUser ^. name) user <- createUser connection newUser org <- createOrganization connection newOrganization addUserToOrganization connection user org

withTransaction conn $ do createUserAndOrganization conn newUser somethingElse conn

types to the rescue

lookupUser :: Connection -> Text -> IO (Maybe User)lookupUser :: Text -> PGTransaction (Maybe User)

runPGTransaction :: PGTransaction a -> Postgres.Connection -> IO a

createUserAndOrganization :: NewUser -> PGTransaction ()createUserAndOrganization newUser = let newOrganization = NewOrganization (newUser ^. name) user <- createUser newUser org <- createOrganization newOrganization addUserToOrganization user org

foo = do createUserAndOrganization newUser somethingElse

runPGTransaction foo connection

notAllowed = do user <- createUser newUser someSlowSideEffectingThing return user

notAllowed = do user <- createUser newUser someSlowSideEffectingThing :: IO () return user

postgresql-transactionalgithub.com/helium/postgresql-transactional

build deploy monitor test develop

Reid Draper @reiddrapergithub.com/helium

helium.com