![EXPRESSIVE SYNTAX (1)
size xs = loop xs 0
where
loop [] acc = acc
loop (_ : xs) acc = loop xs (acc + 1)
-- Usage
size [1,2,3]](https://image.slidesharecdn.com/slides-161201084543/85/2016-11-12-02-Java-Haskell-7-320.jpg)
![EXPRESSIVE SYNTAX (2)
The type of size aboveThe type of size above
In generalIn general
size :: [t] -> Integer -- ?
size :: Num a => [t] -> a -- actuall type
f :: (C1 a) => a -> b -> c -> d -> e
(f a1) :: b -> c -> d -> e
(f a1 b1) :: c -> d -> e
(f a1 b1 c1) :: d -> e
(f a1 b1 c1 d1) :: e](https://image.slidesharecdn.com/slides-161201084543/85/2016-11-12-02-Java-Haskell-8-320.jpg)
![EXPRESSIVE TYPES (4)
ALGEBRAIC DATA TYPES AND PATTERN MATCHING
Constructing values and matchingConstructing values and matching
let z = Zy (Y 123 "Hey" X)
let u1 = User { id = 1, name = "Vasya", day = Mon }
let u2 = User 2 "Petya" Tue
let d = Sat
wd :: Day -> String
wd d | d `elem` [Mon, Tue, Wed, Thu] -> "Working day"
wd d | d `elem` [Sat, Sun] -> "Weekend day"
wd Fri -> "Friday"
case u1 of
User id name day -> ...](https://image.slidesharecdn.com/slides-161201084543/85/2016-11-12-02-Java-Haskell-18-320.jpg)
2016-11-12 02 Николай Линкер. Чему Java может поучиться у Haskell и наоборот
- 2. WHATWHATWHATWHATWHATWHAT WHAT WHAT WHAT WHAT WHAT WHAT WHAT WHAT WHATWHAT JAVA CAN LEARN FROM HASKELLHASKELLHASKELLHASKELLHASKELLHASKELL AND VICE VERSA Nick Linker @nick_linkerNick Linker @nick_linker
- 3. EXAMPLES ( ) Anchor Applikativ Assertible Borders Beautiful_DestinationsAnchor Applikativ Assertible Borders Beautiful_Destinations ByteAlly Capital_MatchByteAlly Capital_Match Chordify CircuitHub CommonwealthChordify CircuitHub Commonwealth Bank DigitalX Elsen Extensibl Facebook FP_CompleteBank DigitalX Elsen Extensibl Facebook FP_Complete FPInsight Front_Row_Education Helium_SystemsFPInsight Front_Row_Education Helium_Systems Hooky,_Inc Infinipool Iris_ConnectHooky,_Inc Infinipool Iris_Connect Keera_StudiosKeera_Studios Kite_&_Lightning Least_Fixed LexisNexis_Risk_SolutionsKite_&_Lightning Least_Fixed LexisNexis_Risk_Solutions Lumi_GuideLumi_Guide Madriska_Inc. Microsoft MidrollMadriska_Inc. Microsoft Midroll MyFansDemand Picus_Security Pivot_Cloud PreziMyFansDemand Picus_Security Pivot_Cloud Prezi Rheo_Systems Scoompa Scrive Scyfy_Technologies SilkRheo_Systems Scoompa Scrive Scyfy_Technologies Silk SimplyRETS Snowdrift.coopSimplyRETS Snowdrift.coop Soostone Stack_BuildersSoostone Stack_Builders Standard_Chartered Stitcher Suite_Solutions SumAllStandard_Chartered Stitcher Suite_Solutions SumAll Swift_Navigation Systor_Vest thoughtbot Tree.isSwift_Navigation Systor_Vest thoughtbot Tree.is Tsuru_Capital Turing_JumpTsuru_Capital Turing_Jump UpHere VaryWell VFILESUpHere VaryWell VFILES Virtual_Forge Wagon Wellposed Well-Typed ZaloreVirtual_Forge Wagon Wellposed Well-Typed Zalore SOURCE
- 4. HASKELL IS ... Functional Pure Lazy (by default) With advanced type system GHC 25 years old, but moves fast last release 2016-05-21
- 5. WHAT JAVA CAN LEARN Expressive syntax Purity Expressive Type System GHCi (REPL) ...
- 8. EXPRESSIVE SYNTAX (2) The type of size aboveThe type of size above In generalIn general size :: [t] -> Integer -- ? size :: Num a => [t] -> a -- actuall type f :: (C1 a) => a -> b -> c -> d -> e (f a1) :: b -> c -> d -> e (f a1 b1) :: c -> d -> e (f a1 b1 c1) :: d -> e (f a1 b1 c1 d1) :: e
- 9. EXPRESSIVE SYNTAX (3) A spherical program in vacuumA spherical program in vacuum module My.Foo where import Data.Time hiding (Day) foo :: IO () foo = do ct <- getCurrentTime putStrLn ("UTC time = " ++ show ct)
- 10. PURITY
- 11. PURITY (1) Seriously, what about file system? Network? Random?Seriously, what about file system? Network? Random?
- 12. PURITY (2) They have the same Java type.They have the same Java type. However, these functions are not interchangeable!However, these functions are not interchangeable! long getLength(String str) { return str.length(); } long getFileLength(String path) { return new File(path).length(); }
- 13. PURITY (3) In Haskell they'd have different types:In Haskell they'd have different types: (Monad tutorial goes here...)(Monad tutorial goes here...) getLength :: String -> Integer getFileLength :: String -> IO Integer
- 14. EXPRESSIVE TYPES
- 15. EXPRESSIVE TYPES (1) NEWTYPES Milliseconds vs seconds Username vs password Paths vs contents Indices In Haskell wrapping can be free!In Haskell wrapping can be free! // call this as runScript("sql/RunStuff.sql") Result runScript(String script) { ...}
- 16. EXPRESSIVE TYPES (2) NEWTYPES Looks like a separate type, but low-level representation isLooks like a separate type, but low-level representation is the same.the same. -- typesafe runScript newtype Path = Path String runScript :: Path -> IO Result
- 18. EXPRESSIVE TYPES (4) ALGEBRAIC DATA TYPES AND PATTERN MATCHING Constructing values and matchingConstructing values and matching let z = Zy (Y 123 "Hey" X) let u1 = User { id = 1, name = "Vasya", day = Mon } let u2 = User 2 "Petya" Tue let d = Sat wd :: Day -> String wd d | d `elem` [Mon, Tue, Wed, Thu] -> "Working day" wd d | d `elem` [Sat, Sun] -> "Weekend day" wd Fri -> "Friday" case u1 of User id name day -> ...
- 19. EXPRESSIVE TYPES (5) TYPE CLASSES Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a type implements an interface from the declaration of the typeimplements an interface from the declaration of the type itselfitself Data Type Eq Ord ToJSON FromJSON Apple Orange More onMore on Intefaces vs TypeclassesIntefaces vs Typeclasses
- 20. EXPRESSIVE TYPES (5) TYPE CLASSES Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a type implements an interface from the declaration of the typeimplements an interface from the declaration of the type itselfitself Data Type Eq Ord ToJSON FromJSON Apple Eq Orange More onMore on Intefaces vs TypeclassesIntefaces vs Typeclasses
- 21. EXPRESSIVE TYPES (5) TYPE CLASSES Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a type implements an interface from the declaration of the typeimplements an interface from the declaration of the type itselfitself Data Type Eq Ord ToJSON FromJSON Apple Eq Ord Orange More onMore on Intefaces vs TypeclassesIntefaces vs Typeclasses
- 22. EXPRESSIVE TYPES (5) TYPE CLASSES Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a type implements an interface from the declaration of the typeimplements an interface from the declaration of the type itselfitself Data Type Eq Ord ToJSON FromJSON Apple Eq Ord Orange Eq More onMore on Intefaces vs TypeclassesIntefaces vs Typeclasses
- 23. EXPRESSIVE TYPES (5) TYPE CLASSES Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a type implements an interface from the declaration of the typeimplements an interface from the declaration of the type itselfitself Data Type Eq Ord ToJSON FromJSON Apple Eq Ord Orange Eq ToJSON More onMore on Intefaces vs TypeclassesIntefaces vs Typeclasses
- 24. EXPRESSIVE TYPES (5) TYPE CLASSES Typeclasses decouple the declaration that a typeTypeclasses decouple the declaration that a type implements an interface from the declaration of the typeimplements an interface from the declaration of the type itselfitself Data Type Eq Ord ToJSON FromJSON Apple Eq Ord Orange Eq ToJSON Lemon Eq Ord ToJSON FromJSON More onMore on Intefaces vs TypeclassesIntefaces vs Typeclasses
- 26. EXPRESSIVE TYPES (7) IT IS POSSIBLE TO CHECK AT COMPILE TIME Arrays bounds Open vs closed files Nested transactions Guaranteed closing resources REST endpoints And test are available too!
- 27. AND MANY MORE
- 28. WHAT HASKELL CAN LEARN Flat learning curve Intellij IDEA Stackoverflow ...
- 31. LEARNING CURVE (2) THINGS TO LEARN IN HASKELL 1. Syntax, functions from Prelude 2. Monads 3. Concurrency & parallelism, STM 4. Libraries 1. Monad transformers 2. Free monads, recursive schemes 3. Arrows, Lens, Type families 4. Type safe DSLs, TH 5. Whatever you want
- 33. INTELLIJ IDEA There is no analog for Haskell.There is no analog for Haskell. There are plugins/extensions forThere are plugins/extensions for Atom Vim Emacs Sublime However, Haskell's stepping debugger (GHCi) is notHowever, Haskell's stepping debugger (GHCi) is not universal.universal.
- 34. STACKOVERFLOW AND DOCS For Java it is easy to find examples and goodFor Java it is easy to find examples and good documentation.documentation. For HaskellFor Haskell The documentation is often poor Needed to look into the libraries' code Fortunately I could ask my colleagues directly.
- 35. OUR CASE
- 36. OUR CASE 1. There were communication problems inside the team 2. There was a split between haskellers and javaists 3. ...Despite the pretty good quality of the services itself 4. The productivity would not save us :-/
- 37. OUR CASE 1. There were communication problems inside the team 2. There was a split between haskellers and javaists 3. ...Despite the pretty good quality of the services itself 4. The productivity would not save us :-/ One should take the social aspects into accountOne should take the social aspects into account during theduring the introduction of the new technologies.introduction of the new technologies.
- 38. SO?
- 39. IS IT WORTH TO USE HASKELL IN PRODUCTION? 1. Only if all team members are eager to learn Haskell 2. Maybe for some separate task, e.g. compiler 3. I believe one can grow a team of Haskellers 4. .. but cannot easy switch team to Haskell (you cannot force people to learn) Examples: GHC, Corrode, Elm, PureScript, Agda,Examples: GHC, Corrode, Elm, PureScript, Agda, Kaleidoscope, PandocKaleidoscope, Pandoc Haskell is not for Production and Other Tales, Katie MillerHaskell is not for Production and Other Tales, Katie Miller andandVideoVideo SlidesSlides
- 40. IS IT WORTH TO LEARN HASKELL? (1) YES! 1. to get a new way of thinking and to push the boundaries 2. to know how to structure things without inheritance 3. to know the alternatives to the buzzwords: DDD, Anemic, Patterns, IOC, SOLID, DI, ... 4. to finally understand monads
- 41. IS IT WORTH TO LEARN HASKELL? (2) OO is full of design problemsOO is full of design problems is hard to get it done right a lot of buzzwords as opposite to algorithms there is no clear criteria whether is one solution better than another cow.eat(grass) grass.beEatenBy(cow) field.eatingInteraction(cow, grass)
- 43. QUESTIONS?