Haskell All the Way Down

Talk on my experience building a codebase from scratch using Haskell

Transcript

1. Arnaud Bailly
   arnaud@capital-match.com
   http://www.capital-match.com
   @abailly
   1
   Haskell All the Way Down
   Building a startup using Haskell
   

   View Slide

2. Functional Programmers Paris - 2015-04-01
   Agenda
   ▪ Who/Why/What
   ▪ How we use Haskell
   ▪ The Good, the Bad and the Ugly
   ▪ Future work
   !
   This is not a Monad tutorial….
   2
   

   View Slide

3. Functional Programmers Paris - 2015-04-01
   Who? What? Why?
   3
   

   View Slide

4. Functional Programmers Paris - 2015-04-01
   Who?
   ▪ Pawel Kuznicki
   – CEO, ex-Rocket, ex-McKinsey, ex-Zalora
   ▪ Kevin Lim
   – CFO, ex-JPMorgan, ex-SCB
   ▪ Arnaud Bailly
   – 20+ years experience, mostly Java for food,
   discovered Haskell in 2001
   ▪ Willem van den Ende
   ▪ 20+ years experience, XP since the
   beginning, Smalltalk/Clojure/.Net…
   4
   

   View Slide

5. Functional Programmers Paris - 2015-04-01
   !
   What? Marketplace Lending!
   ~S$32,400 repayment in 1
   year
   Bank
   P2P
   lending
   Bank n lenders
   n deposits = S$30,000

   @ 1.5% interest rate
   SME(borrower)
   S$30,000 loan @ 8%
   ~S$30,450 repayment in 1
   year
   Return of 6.5%
   or S$1,950
   ~S30,500
   or 1.5%
   RETURN
   5
   Capital Match
   Lender 1
   Lender 2
   Lender 3
   SME(borrower)
   Loan syndication on
   behalf of the
   lenders
   S$30,000 loan @ 6.3%
   1%+ underwriting fee = S
   $300-400
   S$5,000 loan @ 7%
   S$5,000 loan @ 7%
   S$20,000 loan @ 6%
   ~S$31,900 repayment in 1
   year ~S$31,500 repayment
   20% commission on
   returns = S$400
   ~S20,960
   or 4.8%
   ~S$5,280
   or 5.6%
   ~S$5,280
   or 5.6%
   1% provisional fund = S$300
   Provis. Fund
   

   View Slide

6. Functional Programmers Paris - 2015-04-01
   Why Haskell?
   ▪ Pawel had very good experience working with
   Haskell developers at previous job
   ▪ He posted job offer on http://functionaljobs.com
   ▪ I wanted to do some real stuff in Haskell
   ▪ I had good experience working for people in
   Singapore
   ▪ It seems fun!
   Let’s do it!
   6
   

   View Slide

7. Functional Programmers Paris - 2015-04-01
   How we use Haskell?
   7
   

   View Slide

8. Functional Programmers Paris - 2015-04-01
   (Nearly) Everything!
   ▪ Dev. Env ⟶ ghc-mod, stylish-haskell
   ▪ Web Backend ⟶ Scotty, Blaze
   ▪ Database ⟶ Custom Event Sourcing
   ▪ Unit/Integration Testing ⟶ HSpec, QuickCheck
   ▪ End-to-End Testing ⟶ hs-webdriver
   ▪ Build ⟶ Cabal, Shake
   ▪ CI Server ⟶ Bake
   ▪ Configuration Management ⟶ Propellor
   8
   

   View Slide

9. Functional Programmers Paris - 2015-04-01
   For the rest…
   ▪ Web Front-end ⟶ Om/Clojurescript
   ▪ Version Control ⟶ Git (what else?)
   ▪ Packaging & Deployment ⟶ Docker (because
   we can)
   ▪ Infrastructure ⟶ DigitalOcean / S3
   ▪ Monitoring ⟶ Riemann, collectd (WIP)
   9
   

   View Slide

10. Functional Programmers Paris - 2015-04-01
    Emacs Dev. Envt.
    10
    Compilation FlyCheck
    HLint
    Autocompletion
    

    View Slide

11. Functional Programmers Paris - 2015-04-01
    Scotty: REST Endpoints
    11
    

    View Slide

12. Functional Programmers Paris - 2015-04-01
    Scotty: Middleware
    12
    

    View Slide

13. Functional Programmers Paris - 2015-04-01
    Blaze: Template HTML
    13
    

    View Slide

14. Functional Programmers Paris - 2015-04-01
    HSpec: Integration Tests
    14
    

    View Slide

15. Functional Programmers Paris - 2015-04-01
    QuickCheck
    15
    

    View Slide

16. Functional Programmers Paris - 2015-04-01
    hs-webdriver: ETE Testing
    16
    

    View Slide

17. Functional Programmers Paris - 2015-04-01
    Shake: Better make
    17
    

    View Slide

18. Functional Programmers Paris - 2015-04-01
    Bake: CI
    18
    

    View Slide

19. Functional Programmers Paris - 2015-04-01
    Propellor: Config Mgt.
    19
    

    View Slide

20. Functional Programmers Paris - 2015-04-01
    The Good, the Bad and the Ugly
    20
    

    View Slide

21. Functional Programmers Paris - 2015-04-01
    The Good
    ▪ Safer programming (shines in comparison with
    front-end dev) thanks to typing and compilation
    ▪ Types really help a lot: Documentation,
    intention, design, checking…
    ▪ Libraries and tools are most often good or very
    good even when in “beta" or “alpha" (e.g. bake)
    ▪ Nice and supportive maintainers and
    community
    ▪ We feel productive and confident to ship haskell
    code: Static Typing + Tests Rock!
    21
    

    View Slide

22. Functional Programmers Paris - 2015-04-01
    The Good (contd.)
    ▪ Refactoring is easier: Change a type and fix
    compiler’s errors
    ▪ Good for hiring: Haskell attracts “interesting"
    people
    ▪ Very easy to replace clunky scripts with
    typesafe and compiled DSL
    22
    

    View Slide

23. Functional Programmers Paris - 2015-04-01
    The Bad
    ▪ Cabal
    – but does its job, no binary packages possible
    and there is Shake for funky stuff
    ▪ Dev. Env. is still not on par with Eclipse/IntelliJ/
    VS
    – but FPComplete and others are making
    progress fast and tooling improves
    ▪ Compilation typing errors
    – but you get accustomed to it once your code
    base is stable
    23
    

    View Slide

24. Functional Programmers Paris - 2015-04-01
    The Bad (contd.)
    ▪ Hiring: Hard to do if you require local people,
    Haskell communities are usually small. Be
    prepared to work remotely
    ▪ Can get pretty abstract pretty quickly…
    – pair programming and peer reviews to the
    rescue!
    24
    

    View Slide

25. Functional Programmers Paris - 2015-04-01
    The Ugly
    ▪ String vs. Data.Text vs. Data.Text.Lazy vs.
    – ⟶ Oh My! Haskell is Old!
    ▪ Runtime error reporting
    – ⟶ No Stack Traces!
    ▪ Aeson deserialization errors
    – ⟶ Cryptic No Parse
    ▪ Conflicting GHC versions/Libs requirements
    ▪ Lazy I/O can bite you
    25
    

    View Slide

26. Functional Programmers Paris - 2015-04-01
    Future Work
    26
    

    View Slide

27. Functional Programmers Paris - 2015-04-01
    Platform
    ▪ Replace clojurescript with Haskell based React
    bindings ⟶ ghcjs
    ▪ Generate CSS ⟶ Clay
    ▪ Replace Scotty with Servant for typesafe routes
    ▪ Improve End-to-End testing
    ▪ Performance and resilience testing ⟶ jepsen
    ▪ Distributed micro-services ⟶ Raft, Cloud
    Haskell
    27
    

    View Slide

28. Functional Programmers Paris - 2015-04-01
    Tooling
    ▪ Improve CI:
    – handle multiple branches, parallel builds,
    better reporting
    ▪ Improve configuration management
    – replace scripts w/ Haskell code for
    provisioning, better propellor configs
    ▪ Better containers builds and orchestration
    28
    

    View Slide

29. Functional Programmers Paris - 2015-04-01
    Credit Risk Analysis
    ▪ Build a database and inference engine to better
    automate Credit Risk Assessment process
    – NLP, ML, Big Data…
    29
    

    View Slide

30. Functional Programmers Paris - 2015-04-01 30
    We are hiring!
    \
    http://functionaljobs.com/jobs/8802-full-stack-software-engineer-at-capital-match
    

    View Slide

31. Functional Programmers Paris - 2015-04-01
    Questions?
    31
    

    View Slide