Try Cats

Scalaの関数型ライブラリCatsをやってみた話です。

1. 5SZ
   $BUT  
2. ΞδΣϯμ w $BUTͱ͸
   w $BUTಠࣗͷϞφυ
   w $BUTΛ௨ֶͯ͠Μͩ͜ͱ
3. $BUTͱ͸ 4DBMB[ͷ಺෦෼྾ʹΑͬͯੜ·Εͨ
   ؔ਺ܕϓϩάϥϛϯά༻ͷ4DBMBϥΠϒϥϦ ɾ೥ࠒ஀ੜ
   ɾʹWϦϦʔε
   ɾݍ DBUFHPSZ ʹ༝དྷ ಡΜͩจݙ ɾೣ൪
   IUUQFFETJODPNIFSEJOHDBUTKB
   ɾ4DBMB
   8JUI
   $BUT
4. $BUTͷಛ௃ ɾؔ਺ܕϓϩάϥϛϯάΛ࣮ݱ͢ΔͨΊͷ
   ๛෋ͳܕΫϥεͷఏڙ ɾIBTLFMMʹ͍࣮ۙ૷ &Rɺ4IPXͳͲ
5. $BUT
   WT
   4DBMB[ $BUT ɾ৽͍͠σʔλܕ
   ɾ࣮༻্ඞཁͳશͯͷ൚༻ؔ਺ͷ࣮૷
   
   ΞυϗοΫଟ૬ੑɺUSBJU
   
   JNQMJDJU ೣ൪ΑΓҾ༻ 4DBMB[ ɾ৽͍͠σʔλܕ
   ɾඪ४Ϋϥεͷ֦ு 0QUJPO0QT
   -JTU0QT
   ɾ࣮༻্ඞཁͳશͯͷ൚༻ؔ਺ͷ࣮૷
   
   ΞυϗοΫଟ૬ੑɺUSBJU
   
   JNQMJDJU ಠश4DBMB[ΑΓҾ༻
6. $BUT
   WT
   4DBMB[ &JUIFS
   
   
   
   
   
   
   a
   7BMJEBUFE
   
   
   
   7BMJEBUJPO
   3FBEFS
   
   
   3FBEFS
   4UBUF
   
   
   4UBUF
   8SJUFS
   
   
   8SJUFS ɾ༻ҙ͞Ε͍ͯΔϝιου͕Ұ෦ҟͳΔ͕ɺ
   ಉ͡Α͏ͳσʔλܕ͕͋Δ
7. $BUTಠࣗͷϞφυ ɾ&WBM
8. &WBMϞφυ ධՁΛ੍ޚ͢Δσʔλܕ import cats.Eval // valͷΑ͏ʹఆٛ࣌ʹධՁ val x = Eval.now { println("Computing X") math.random } // Computing X // x: cats.Eval[Double] = Now(0.8724950064732552) // defͷΑ͏ʹৗʹධՁ val y = Eval.always { println("Computing Y") math.random } // y: cats.Eval[Double] = cats.Always@5212e1f5 // lazy valͷΑ͏ʹ஗ԆධՁ val z = Eval.later { println("Computing Z") math.random } // z: cats.Eval[Double] = cats.Later@33eda11
9. &WBMϞφυ ධՁΛ੍ޚ͢Δσʔλܕ x.value // first access // res9: Double = 0.8724950064732552 x.value // second access // res10: Double = 0.8724950064732552 y.value // first access // Computing Y // res11: Double = 0.8795680260041828 y.value // second access // Computing Y // res12: Double = 0.5640213059400854 z.value // first access // Computing Z // res13: Double = 0.5813583535421343 z.value // second access // res14: Double = 0.5813583535421343 import cats.Eval // valͷΑ͏ʹఆٛ࣌ʹධՁ val x = Eval.now { println("Computing X") math.random } // Computing X // x: cats.Eval[Double] = Now(0.8724950064732552) // defͷΑ͏ʹৗʹධՁ val y = Eval.always { println("Computing Y") math.random } // y: cats.Eval[Double] = cats.Always@5212e1f5 // lazy valͷΑ͏ʹ஗ԆධՁ val z = Eval.later { println("Computing Z") math.random } // z: cats.Eval[Double] = cats.Later@33eda11
10. &WBMʹΑΔ࠶ؼॲཧ def factorial(n: BigInt): BigInt = if(n == 1) n else n * factorial(n - 1) factorial(50000) // ࣮ߦ ຤ඌ࠶ؼͰͳ͍࠶ؼؔ਺
11. &WBMʹΑΔ࠶ؼॲཧ def factorial(n: BigInt): BigInt = if(n == 1) n else n * factorial(n - 1) factorial(50000) // ࣮ߦ ຤ඌ࠶ؼͰͳ͍࠶ؼؔ਺ ελοΫΦʔόʔϑϩʔ͕ى͖Δ factorial(50000) // java.lang.StackOverflowError // ...
12. &WBMʹΑΔ࠶ؼॲཧ def factorial(n: BigInt): Eval[BigInt] = if(n == 1) { Eval.now(n) } else { factorial(n - 1).map(_ * n) } factorial(50000).value // ࣮ߦ &WBMΛ༻͍ͨίʔυʹมߋ
13. &WBMʹΑΔ࠶ؼॲཧ def factorial(n: BigInt): Eval[BigInt] = if(n == 1) { Eval.now(n) } else { factorial(n - 1).map(_ * n) } factorial(50000).value // ࣮ߦ &WBMΛ༻͍ͨίʔυʹมߋ factorial(50000).value // java.lang.StackOverflowError // ... ελοΫΦʔόʔϑϩʔ͕ى͖Δ
14. &WBMʹΑΔ࠶ؼॲཧ def factorial(n: BigInt): Eval[BigInt] = if(n == 1) { Eval.now(n) } else { Eval.defer(factorial(n - 1).map(_ * n)) } factorial(50000).value // ࣮ߦ // res20: BigInt = //33473205095971448369154760940714864779127732…… &WBMEFGFSϝιουΛ࢖ͬͯ͞ΒʹϦϑΝΫλϦϯά
15. &WBMʹΑΔ࠶ؼॲཧ def factorial(n: BigInt): Eval[BigInt] = if(n == 1) { Eval.now(n) } else { Eval.defer(factorial(n - 1).map(_ * n)) } factorial(50000).value // ࣮ߦ // res20: BigInt = //33473205095971448369154760940714864779127732…… factorial(50000).value // res20: BigInt = //33473205095971448369154760940714864779127732…… &WBMEFGFSϝιουΛ࢖ͬͯ͞ΒʹϦϑΝΫλϦϯά ਖ਼ৗऴྃ
16. &WBMʹΑΔ࠶ؼॲཧ &WBMEFGFSϝιου͸ԿΛ͍ͯ͠Δͷ͔ʁ def defer[A](a: => Eval[A]): Eval[A] = new Eval.Defer[A](a _) {} sealed abstract class Defer[A](val thunk: () => Eval[A]) extends Eval[A] { def memoize: Eval[A] = Memoize(this) def value: A = evaluate(this) } &WBM<">Λฦ͢ܭࢉΛ஗Ԇ͍ͯ͠Δ τϥϯϙϦϯԽ͕ߦΘΕɺؔ਺͕਺चͭͳ͗
    Ͱݺ͹Εͳ͘ͳΔ
17. $BUTΛษڧֶͯͯ͠Μͩ͜ͱ ಡΜͩจݙ ɾೣ൪
    IUUQFFETJODPNIFSEJOHDBUTKB
    ɾ4DBMB
    8JUI
    $BUT ֶͼ ɾϞφυͬͯԿͳͷ͔
    ɾ,MFJTMJɺ3FBEFSϞφυ
    ɾϞφυม׵ࢠ
18. ϞφυͬͯԿͳͷ͔ Ϟφυͱ͸ɺ݁߹཯ͱಉҰ཯Λຬͨ͢࠷খݶͷ
    ϞφυίϯϏωʔλͷू·Γͷ͍ͣΕ͔Λ࣮૷ͨ͠΋ͷͰ͋Δɻ ΧϥʔίοϓຊΑΓҾ༻
19. ϞφυͬͯԿͳͷ͔ Ϟφυͱ͸ɺ݁߹཯ͱಉҰ཯Λຬͨ͢࠷খݶͷ
    ϞφυίϯϏωʔλͷू·Γͷ͍ͣΕ͔Λ࣮૷ͨ͠΋ͷͰ͋Δɻ ʁ ΧϥʔίοϓຊΑΓҾ༻
20. ϞφυͬͯԿͳͷ͔ ϞφυΛඥղ͘Ωʔϫʔυ ɾϑΝϯΫλʔ 'VODUPS
    ɾΞϓϦΧςΟϒϑΝϯΫλʔ "QQMJDBUJWF
    'VODUPS ͜ͷೋͭ͸ඞͣग़ͯ͘Δ Ϟφυͱ͸ɺ݁߹཯ͱಉҰ཯Λຬͨ͢࠷খݶͷ
    ϞφυίϯϏωʔλͷू·Γͷ͍ͣΕ͔Λ࣮૷ͨ͠΋ͷͰ͋Δɻ ʁ ΧϥʔίοϓຊΑΓҾ༻
21. Ϟφυ 'VODUPS
    
    "QQMZ
    
    "QQMJDBUJWF
    'VODUPS
    
    .POBE DBUTʹ͓͍ͯɺ࣍ͷॱͰਐԽ͍ͯ͘͠
22. 'VODUPS -JTU
    0QUJPOͳͲʹରͯ͠ɺ
    แ·Εͨ஋ʹରͯ͠Ҿ਺ؔ਺Λద༻͢ΔॲཧΛఏڙ͢ΔܕΫϥε List(1, 2, 3).map(_ * 2) // List(2, 4, 6) Some(1).map(_ * 2) // Some(2) @typeclass trait Functor[F[_]] extends functor.Invariant[F] { self => def map[A, B](fa: F[A])(f: A => B): F[B] .... }
23. "QQMZ 'VODUPSΛ֦ுͯ͠ɺ/ݸͷ'VODUPS஋ʹ/Ҿ਺ؔ਺Λ
    ద༻͢ΔॲཧΛఏڙ͢ΔܕΫϥε import cats.implicits._ // implicit defͰ҉໧తʹmap2, map3͕ద༻͞ΕΔ (Some(1), Some(2)).mapN(_ + ) // Some(3) (Some(1), Some(2), Some(3)).mapN(_ * _ * _) // Some(6) (List("ha", "heh", "hmm"), List("?", "!", ".")) mapN {_ + _} // List(ha?, ha!, ha., heh?, heh!, heh., hmm?, hmm!, hmm.)
24. "QQMJDBUJWF
    'VODUPS "QQMJDBUJWF͸"QQMZʹ
    QVSFϝιου "
    
    '<"> Λ௥Ճ͍ͯ͠ΔܕΫϥε ϓϦϛςΟϒ஋Λ"QQMJDBUJWFܕʹม׵ͯ͠ɺ
    ଞͷ"QQMJDBUJWFͱ߹੒Ͱ͖Δɹ DBUTͷ7BMJEBUFE͸BQQMJDBUJWF
    GVODUPS
    Λܗ੒͢Δ 1.pure[Option] // Some(1) // શͯͷΠϕϯτΛݕূ্ͨ͠Ͱɺ߹੒Λߦ͏ val result = (valid[String, String]("event 1 ok") |@| invalid[String, String]("event 2 failed!") |@| invalid[String, String]("event 3 failed!")) map {_ + _ + _} // result: cats.data.Validated[String,String] = Invalid(event 2 failed!event 3 failed!) DPNQPTF G
    QVSF
    
    G
    DPNQPTF QVSF
    G
    
    G QVSF͸ಉҰ཯Λຬͨ͢
25. .POBE "QQMJDBUJWF
    'VODUPS͸ෳ਺ͷ'VODUPS஋Λѻ͏͜ͱ͕Ͱ͖͕ͨɺ
    લͷ'VODUPS஋ʹґଘ͢ΔॲཧΛॻ͚ͳ͍ɻ def hogeOption(a: Int): Option[Int] = Some(a) hogeOption(1).flatMap(a => hogeOption(a).map(b => a+b)) // Some(2) for { a <- hogeOption(1) b <- hogeOption(a) } yield (a + b) // Some(2) .POBE͸લͷ஋ʹґଘ͢ΔॲཧΛఏڙ͢ΔܕΫϥε /POFqBU.BQ G qBU.BQ H
    
    /POFqBU.BQ B
    
    G B qBU.BQ H qBU.BQ͸݁߹཯Λຬͨ͢
26. Ϟφυ·ͱΊ Ϟφυͱ͸ɺ݁߹཯ͱಉҰ཯Λຬͨ͢࠷খݶͷ
    ϞφυίϯϏωʔλͷू·Γͷ͍ͣΕ͔Λ࣮૷ͨ͠΋ͷͰ͋Δɻ DPNQPTF G
    QVSF
    
    G
    DPNQPTF QVSF
    G
    
    G ಉҰ཯ /POFqBU.BQ G qBU.BQ H
    
    
    /POFqBU.BQ B
    
    G B qBU.BQ H ݁߹཯ ஋ʹแ·Εͨ΋ͷʹରͯ͠ɺؔ਺ͷ࿈࠯Λ࣮ߦͰ͖Δ