Haskell all the way down

Transcript

1. Haskell SG - 2015-05-06
   BreizhCamp 2015 #BzhCmp
   /dev/summer 2015 #devsummer
   Arnaud Bailly - Willem van den Ende
   arnaud@capital-match.com - willem@qwan.eu
   http://www.capital-match.com
   @abailly - @mostalive
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   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….
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3. Haskell SG - 2015-05-06
   BreizhCamp 2015 #BzhCmp
   /dev/summer 2015 #devsummer
   Who? What? Why?
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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
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   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!
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6. /dev/summer 2015 #devsummer
   System Overview
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7. /dev/summer 2015 #devsummer
   Application Architecture
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8. Haskell SG - 2015-05-06
   BreizhCamp 2015 #BzhCmp
   /dev/summer 2015 #devsummer
   How we use Haskell?
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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
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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)
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11. /dev/summer 2015 #devsummer
    HSpec: Integration Tests
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12. /dev/summer 2015 #devsummer
    hs-webdriver: ETE Testing
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13. /dev/summer 2015 #devsummer
    Shake: Better make
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14. /dev/summer 2015 #devsummer
    Bake: CI
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15. /dev/summer 2015 #devsummer
    Propellor: Config Mgt.
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16. Haskell SG - 2015-05-06
    BreizhCamp 2015 #BzhCmp
    /dev/summer 2015 #devsummer
    The Good, the Bad and the Ugly
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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!
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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
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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
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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!
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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
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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
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23. Haskell SG - 2015-05-06
    BreizhCamp 2015 #BzhCmp
    /dev/summer 2015 #devsummer
    Questions?
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