Try Cats

Scalaの関数型ライブラリCatsをやってみた話です。

Transcript

1. 5SZ$BUT
   
   
   

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2. ΞδΣϯμ
   w $BUTͱ͸
   w $BUTಠࣗͷϞφυ
   w $BUTΛ௨ֶͯ͠Μͩ͜ͱ
   

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3. $BUTͱ͸
   4DBMB[ͷ಺෦෼྾ʹΑͬͯੜ·Εͨ
   ؔ਺ܕϓϩάϥϛϯά༻ͷ4DBMBϥΠϒϥϦ
   ɾ೥ࠒ஀ੜ
   ɾʹWϦϦʔε
   ɾݍ DBUFHPSZ
   ʹ༝དྷ
   ಡΜͩจݙ
   ɾೣ൪IUUQFFETJODPNIFSEJOHDBUTKB
   ɾ4DBMB8JUI$BUT
   

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4. $BUTͷಛ௃
   ɾؔ਺ܕϓϩάϥϛϯάΛ࣮ݱ͢ΔͨΊͷ
   ๛෋ͳܕΫϥεͷఏڙ
   ɾIBTLFMMʹ͍࣮ۙ૷ &Rɺ4IPXͳͲ
   
   

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5. $BUTWT4DBMB[
   $BUT
   ɾ৽͍͠σʔλܕ
   ɾ࣮༻্ඞཁͳશͯͷ൚༻ؔ਺ͷ࣮૷
   ΞυϗοΫଟ૬ੑɺUSBJUJNQMJDJU
   
   ೣ൪ΑΓҾ༻
   4DBMB[
   ɾ৽͍͠σʔλܕ
   ɾඪ४Ϋϥεͷ֦ு 0QUJPO0QT -JTU0QT
   
   ɾ࣮༻্ඞཁͳશͯͷ൚༻ؔ਺ͷ࣮૷
   ΞυϗοΫଟ૬ੑɺUSBJUJNQMJDJU
   
   ಠश4DBMB[ΑΓҾ༻
   

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6. $BUTWT4DBMB[
   &JUIFSa
   7BMJEBUFE7BMJEBUJPO
   3FBEFS3FBEFS
   4UBUF4UBUF
   8SJUFS8SJUFS
   ɾ༻ҙ͞Ε͍ͯΔϝιου͕Ұ෦ҟͳΔ͕ɺ
   ಉ͡Α͏ͳσʔλܕ͕͋Δ
   

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7. $BUTಠࣗͷϞφυ
   ɾ&WBM
   

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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
   

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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
   

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10. &WBMʹΑΔ࠶ؼॲཧ
    def factorial(n: BigInt): BigInt =
    if(n == 1) n else n * factorial(n - 1)
    factorial(50000) // ࣮ߦ
    ຤ඌ࠶ؼͰͳ͍࠶ؼؔ਺
    

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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
    // ...
    

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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
    

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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
    

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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
    

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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
    

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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)
    }
    &WBMΛฦ͢ܭࢉΛ஗Ԇ͍ͯ͠Δ
    τϥϯϙϦϯԽ͕ߦΘΕɺؔ਺͕਺चͭͳ͗
    Ͱݺ͹Εͳ͘ͳΔ
    

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17. $BUTΛษڧֶͯͯ͠Μͩ͜ͱ
    ಡΜͩจݙ
    ɾೣ൪IUUQFFETJODPNIFSEJOHDBUTKB
    ɾ4DBMB8JUI$BUT
    ֶͼ
    ɾϞφυͬͯԿͳͷ͔
    ɾ,MFJTMJɺ3FBEFSϞφυ
    ɾϞφυม׵ࢠ
    

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18. ϞφυͬͯԿͳͷ͔
    Ϟφυͱ͸ɺ݁߹཯ͱಉҰ཯Λຬͨ͢࠷খݶͷ
    ϞφυίϯϏωʔλͷू·Γͷ͍ͣΕ͔Λ࣮૷ͨ͠΋ͷͰ͋Δɻ
    ΧϥʔίοϓຊΑΓҾ༻
    

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19. ϞφυͬͯԿͳͷ͔
    Ϟφυͱ͸ɺ݁߹཯ͱಉҰ཯Λຬͨ͢࠷খݶͷ
    ϞφυίϯϏωʔλͷू·Γͷ͍ͣΕ͔Λ࣮૷ͨ͠΋ͷͰ͋Δɻ
    ʁ
    ΧϥʔίοϓຊΑΓҾ༻
    

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20. ϞφυͬͯԿͳͷ͔
    ϞφυΛඥղ͘Ωʔϫʔυ
    ɾϑΝϯΫλʔ 'VODUPS
    
    ɾΞϓϦΧςΟϒϑΝϯΫλʔ "QQMJDBUJWF'VODUPS
    
    ͜ͷೋͭ͸ඞͣग़ͯ͘Δ
    Ϟφυͱ͸ɺ݁߹཯ͱಉҰ཯Λຬͨ͢࠷খݶͷ
    ϞφυίϯϏωʔλͷू·Γͷ͍ͣΕ͔Λ࣮૷ͨ͠΋ͷͰ͋Δɻ
    ʁ
    ΧϥʔίοϓຊΑΓҾ༻
    

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21. Ϟφυ
    'VODUPS"QQMZ
    "QQMJDBUJWF'VODUPS.POBE
    DBUTʹ͓͍ͯɺ࣍ͷॱͰਐԽ͍ͯ͘͠
    

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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]
    ....
    }
    

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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.)
    

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24. "QQMJDBUJWF'VODUPS
    "QQMJDBUJWF͸"QQMZʹ
    QVSFϝιου "'
    Λ௥Ճ͍ͯ͠ΔܕΫϥε
    ϓϦϛςΟϒ஋Λ"QQMJDBUJWFܕʹม׵ͯ͠ɺ
    ଞͷ"QQMJDBUJWFͱ߹੒Ͱ͖Δɹ
    DBUTͷ7BMJEBUFE͸BQQMJDBUJWFGVODUPSΛܗ੒͢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
    

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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 b } yield (a + b)
    // Some(2)
    .POBE͸લͷ஋ʹґଘ͢ΔॲཧΛఏڙ͢ΔܕΫϥε
    /POFqBU.BQ G
    qBU.BQ H
    /POFqBU.BQ BG B
    qBU.BQ H
    
    
    qBU.BQ͸݁߹཯Λຬͨ͢
    

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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 BG B
    qBU.BQ H
    
    
    ݁߹཯
    ஋ʹแ·Εͨ΋ͷʹରͯ͠ɺؔ਺ͷ࿈࠯Λ࣮ߦͰ͖Δ
    

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