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Haskell all the way down

Haskell all the way down

Arnaud Bailly

June 27, 2015
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  1. Haskell SG - 2015-05-06
    BreizhCamp 2015 #BzhCmp
    /dev/summer 2015 #devsummer
    Arnaud Bailly - Willem van den Ende
    [email protected] - [email protected]
    http://www.capital-match.com
    @abailly - @mostalive
    1
    Haskell All the Way Down
    Continuous deployment in an early stage startup

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  2. /dev/summer 2015 #devsummer
    Agenda
    ▪ Who/Why/What
    ▪ How we use Haskell
    ▪ The Good, the Bad and the Ugly
    ▪ Future work
    This is not a Monad tutorial….
    2

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  3. Haskell SG - 2015-05-06
    BreizhCamp 2015 #BzhCmp
    /dev/summer 2015 #devsummer
    Who? What? Why?
    3

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  4. /dev/summer 2015 #devsummer
    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
    4
    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

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  5. /dev/summer 2015 #devsummer
    Why did we start with 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 seemed fun!
    Let’s do it!
    5

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  6. /dev/summer 2015 #devsummer
    System Overview
    6

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  7. /dev/summer 2015 #devsummer
    Application Architecture
    7

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  8. Haskell SG - 2015-05-06
    BreizhCamp 2015 #BzhCmp
    /dev/summer 2015 #devsummer
    How we use Haskell?
    8

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  9. /dev/summer 2015 #devsummer
    For (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
    9

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  10. /dev/summer 2015 #devsummer
    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)
    10

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  11. /dev/summer 2015 #devsummer
    HSpec: Integration Tests
    11

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  12. /dev/summer 2015 #devsummer
    hs-webdriver: ETE Testing
    12

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  13. /dev/summer 2015 #devsummer
    Shake: Better make
    13

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  14. /dev/summer 2015 #devsummer
    Bake: CI
    14

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  15. /dev/summer 2015 #devsummer
    Propellor: Config Mgt.
    15

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  16. Haskell SG - 2015-05-06
    BreizhCamp 2015 #BzhCmp
    /dev/summer 2015 #devsummer
    The Good, the Bad and the Ugly
    16

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  17. /dev/summer 2015 #devsummer
    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!
    17

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  18. /dev/summer 2015 #devsummer
    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
    18

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  19. /dev/summer 2015 #devsummer
    The Bad
    ▪ Cabal
    – but does its job, no binary packages possible
    and there is Shake for funky stuff
    – it is improving (e.g. Stackage, Stack)
    ▪ Dev. Env. is still not on par with Eclipse/IntelliJ/VS
    – but FPComplete and others are making
    progress fast and tooling improves continuously
    ▪ Compilation typing errors
    – but you get accustomed to it once your code
    base is stable
    19

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  20. /dev/summer 2015 #devsummer
    The Bad (contd.)
    ▪ Hiring: Hard to do if you require local people,
    Haskell communities are usually small.
    – but you can work remotely
    ▪ Can get pretty abstract pretty quickly…
    – pair programming and peer reviews to the
    rescue!
    ▪ Reinventing the wheel…
    – but that’s fun!
    20

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  21. /dev/summer 2015 #devsummer
    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
    – ⟶ Cabal Hell, enter Stack!
    ▪ Laziness can bite you
    21

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  22. Haskell SG - 2015-05-06
    BreizhCamp 2015 #BzhCmp
    /dev/summer 2015 #devsummer
    Conclusion
    Haskell really pays off when you embrace
    it fully
    22

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  23. Haskell SG - 2015-05-06
    BreizhCamp 2015 #BzhCmp
    /dev/summer 2015 #devsummer
    Questions?
    23

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