Pattern Matching in Ruby

http://sapporo.rubykaigi.org/2012/en/schedule/details/11.html

Transcript

1. Pattern Matching in Ruby
   Kazuki Tsujimoto
   Nomura Research Institute, Ltd.
   

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2. 自己紹介
   • @k_tsj
   • 好きな言語:
   Ruby/Scheme/Scala
   • CRubyコミッタ
   Self introduction
   Favorite languages:
   A CRuby committer
   

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3. Ruby 2.0
   2013/2/24
   リリース予定
   will be released
   

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4. Ruby 2.0の位置づけ
   • まつもとさん曰く(2007)
   http://www.rubyist.net/~matz/slides/kobe07/index.html (Ruby 1.9を語る)
   Matz said
   Carrot
   Position of Ruby 2.0
   

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5. 新しい人参が必要
   • Multiple VM
   • JIT
   • 世代別/並列GC
   • …
   • パターンマッチ
   We need a new carrot
   Generational/Parallel GC
   Pattern matching
   

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6. パターンマッチとは
   What is pattern matching
   

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7. 辞書的定義
   • データを検索する場合に、特
   定のパターンが出現するかど
   うか、またどこに出現するか
   を特定する手法(Wikipedia)
   Dictionary definition
   Pattern matching is the act of checking a
   perceived sequence of tokens for the presence
   of the constituents of some pattern
   

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8. ?
   

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9. 多重代入
   a, (b, c) = [1, [2, 3]]
   Multiple assignment
   

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10. パターンマッチ
    Array(1, Array(2, 3)) match {
    case Array(a, Array(b, c)) =>
    ...
    }
    Pattern matching
    

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11. 比較
    a, (b, c) = [1, [2, 3]]
    Array(1, Array(2, 3)) match {
    case Array(a, Array(b, c)) =>
    ...
    }
    Comparing
    多重代入
    Multiple assignment
    パターンマッチ
    Pattern matching
    

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12. 多重代入の問題点
    1. Arrayに限定される
    Problems of multiple assignment
    Array only
    

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13. 多重代入の問題点
    a, (b, c), d = [1, [2, 3]]
    d #=> nil
    Problems of multiple assignment
    2. 個数の確認等ができない
    Can not check number of items,etc
    

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14. 多重代入の問題点
    a, (b, c) = [1, [2, 3]]
    これが欲しい
    Problems of multiple assignment
    Need it
    3. 途中の値が代入できない
    Can not assign nonterminal value
    

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15. 多重代入の問題点
    1. Arrayに限定される
    2. 個数の確認等ができない
    3. 途中の式を代入できない
    分解機能が弱い
    照合機能がない
    代入機能が弱い
    Lack of deconstructuring mechanism
    No matching mechanism
    Lack of assignment mechanism
    Problems of multiple assignment
    

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16. パターンマッチとは
    (多重代入 + α) + case
    分解 + 代入 照合
    Deconstructuring Assignment Matching
    Multiple assignment
    What is pattern matching
    

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17. 他言語のパターンマッチ
    Language Support Type Paradigm
    Python Dynamic OOP
    Scheme
    (Library)
    Dynamic FP
    Java Static OOP
    Scala Static OOP+FP
    Haskell Static FP
    F# Static FP
    (C) 2012 Yusuke Kamiyamane. All rights reserved. / Fugue Icons
    Pattern matching in other languages
    OOP: オブジェクト指向プログラミング
    FP: 関数型プログラミング
    

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18. Scalaにおける
    パターンマッチ
    Pattern matching in Scala
    

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19. 基本的な使い方
    Array(1, Array(2, 3)) match {
    case Array(a, Array(b, c)) =>
    Array(a, b, c)
    case _ => null
    }
    // => Array(1, 2, 3)
    Basic usage
    

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20. 分解
    • ArrayをArrayとして
    Array(1, Array(2, 3)) match {
    case Array(a, Array(b, c)) => ...
    }
    Deconstructuring
    Array as Array
    

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21. 分解
    • ListをListとして
    List(1, List(2, 3)) match {
    case List(a, List(b, c)) => ...
    }
    Deconstructuring
    List as List
    

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22. 分解
    • StringをEMailとして
    "foo@example.com" match {
    case EMail(user, domain) =>
    (user, domain)
    }
    //=> ("foo", "example.com")
    String as EMail
    Deconstructuring
    

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23. 分解
    • StringをEMailとして
    "invalid e-mail address" match {
    case EMail(user, domain) =>
    (user, domain)
    }
    //=> MatchError
    String as EMail
    Deconstructuring
    

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24. 分解
    • StringをEMailとして
    "foo@example.com" match {
    case EMail(user, domain) => ...
    }
    #unapply
    String as EMail
    Deconstructuring
    

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25. 分解
    • StringをEMailとして
    object EMail {
    def unapply(str: String): Option[(String, String)] = {
    val parts = str split "@"
    if (parts.length == 2) Some(parts(0), parts(1))
    else None
    }
    }
    String as EMail
    Deconstructuring
    

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26. 分解
    val re = """(¥d+)-(¥d+)-(¥d+)""".r
    // 正規表現オブジェクトの生成
    "2012-09-15" match {
    case re(yyyy, mm, dd) =>
    (yyyy, mm, dd)
    }
    // => ("2012", "09", "15")
    // Create a Regex object
    Deconstructuring
    

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27. 照合
    Array(1, Array(2, 3)) match {
    case Array(a, Array(b, c), d) => null
    case Array(a, List(b, c)) => null
    case Array(0, Array(b, c)) => null
    }
    // => MatchError
    Matching
    

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28. 代入
    Array(1, Array(2, 3)) match {
    case Array(a, d @ Array(b, c)) =>
    Array(a, b, c, d)
    }
    // => Array(1, 2, 3, Array(2, 3))
    Assignment
    

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29. Rubyにおける
    パターンマッチ
    Pattern matching in Ruby
    

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30. pattern-match
    • Scalaのパターンマッチに似た機
    能を実現するためのライブラリ
    – https://github.com/k-tsj/pattern-match
    – gem install pattern-match
    A Scala-like pattern matching library
    

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31. 基本的な使い方
    require 'pattern-match'
    match([0, [1, 2]]) {
    with(Array.(a, Array.(b, 2)) {
    [a, b] #=> [0, 1]
    }
    with(_[a, _[b, 2]]) { # 上記と同様
    ...
    }
    }
    Same as above
    Basic usage
    

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32. 基本的な使い方
    proc = match {
    with(_[a, _[b, 2]]) { [a, b] }
    }
    proc.call([0, [1, 2]]) #=> [0, 1]
    引数なし
    No argument
    Basic usage
    

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33. 分解
    • 分解するために必要なこと
    – Deconstructorのクラスに
    Deconstructableをincludeする
    – Deconstructorに
    deconstructメソッドを定義する
    with(Array.(a, b))
    Deconstructor
    Deconstructuring
    What you need to deconstruct an object
    Include Deconstructable
    in a class of Deconstructor
    Define deconstruct method for Deconstructor
    

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34. 分解
    class Class
    include PatternMatch::Deconstructable
    end
    def Array.deconstruct(val)
    accept_self_instance_only(val)
    val
    end
    Deconstructuring
    

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35. 分解
    class Regexp
    include PatternMatch::Deconstructable
    def deconstruct(val)
    m = Regexp.new("¥¥A#{source}¥¥z",
    options).match(val.to_s)
    raise PatternNotMatch unless m
    m.captures.empty? ? [m[0]] : m.captures
    end
    end
    Deconstructuring
    

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36. 照合/代入
    match([0, [1, 2]]) {
    with(_[a, _[b, c], d]) => nil
    with(_[a, List.(b, c)]) => nil
    with(_[1, _[b, c]]) => nil
    }
    #=> NoMatchingPatternError
    Matching/Assignment
    

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37. 照合/代入
    • オブジェクトの比較は#===
    match([0, 1]) {
    with(_[Fixnum, 1..10]) { true }
    with(_) { false }
    } #=> true
    Matching/Assignment
    Compare objects by #===
    

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38. 照合/代入
    • 繰り返し
    match([[0, 1], [2, 3]]) {
    with(_[_[a, b], ___]) {
    [a, b] #=> [[0, 2], [1, 3]]
    }
    }
    Matching/Assignment
    Repetition
    

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39. 照合/代入
    • 繰り返し
    match([[0, 1], [2, 3]]) {
    with(_[*_[a, b]]) {
    [a, b] #=> [[0, 2], [1, 3]]
    }
    }
    Matching/Assignment
    Repetition
    

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40. 照合/代入
    • AND(&)/OR(|)/NOT(!)
    match([0, [1]]) {
    with(_[(a & Fixnum), !(_[2] | _[3])]) {
    a #=> 0
    }
    }
    Matching/Assignment
    

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41. 照合/代入
    • Hash.()
    –Destructuring Assignment(#6414)
    john = {name: "John", last: "Smith"}
    {name: n, last: l} = john
    n // => "John"
    l // => "Smith"
    Matching/Assignment
    

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42. 照合/代入
    • Hash.()
    –Destructuring Assignment(#6414)
    match({name: "John", last: "Smith"}) {
    with(Hash.(name: n, last: l)) {
    n #=> "John"
    l #=> "Smith"
    }
    }
    Matching/Assignment
    

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43. 照合/代入
    • Object.()
    –Duck typing style
    match(10) {
    with(Object.(:to_i => i, :to_s.(16) => s)) {
    [i, s] #=> [10, "a"]
    }
    }
    Matching/Assignment
    

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44. 利用例(テキスト処理)
    birthday,fullname
    2012/4/1,John Smith
    2011/6/3,Jane Smith
    2012/9/15,Pater Smith
    2012/5/22,Mary Smith
    Year: 2012
    Month: 1 - 6
    Month: 4, Name: John, Last: Smith
    Month: 5, Name: Mary, Last: Smith
    Examples(Text processing)
    入力
    Input
    出力
    Output
    

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45. 利用例(テキスト処理)
    • パターンマッチあり
    ARGF.each(&match {
    with(CSV.(Date.(2012, mm & 1..6, _),
    /(¥w+) (¥w+)/.(name, last))) { ... }
    with(_) { ... }
    })
    Examples(Text processing)
    With pattern matching
    

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46. 利用例(テキスト処理)
    • パターンマッチなし
    ARGF.each do |i|
    cols = CSV.parse_line(i)
    if cols.length == 2
    date = Date.parse(cols[0]) rescue nil
    m = cols[1].match(/(¥w+) (¥w+)/)
    if date and date.year == 2012 and (1..6).includes?(date.month) and m
    mm = date.month
    name, last = m.captures
    ...
    Examples(Text processing)
    Without pattern matching
    

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47. 利用例(ノード処理)
    doc = REXML::Document.new(
    'ab'
    )
    match(doc.root) {
    with(Element('ul', attrs, *Element('li', _, Text(txts)))) {
    txts #=> ["a", "b"]
    }
    }
    Examples(Node processing)
    

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48. デザイン(文法)
    • match式を新設
    • case式を拡張
    • メソッド引数/ブロック引数
    Design(Syntax)
    Add match expression
    Extend case expression
    Method parameters/Block parameters
    

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49. デザイン(分解)
    • コンテキストに応じた分解
    Time.gm(year, mon = 1, day = 1,
    hour = 0, min = 0, sec = 0, usec = 0)
    Time.(year, mon, day, hour, min, sec, usec)
    Time.(year, mon, day)
    Time.(hour, min, sec, usec)
    Design(Deconstructuring)
    Contextual deconstructuring
    

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50. デザイン(照合)
    • 正規表現
    match(["a", "b", 0, "c", "d"]) {
    with(_[*i, Fixnum, *j]) {
    [i, j] #=> [["a", "b"], ["c", "d"]]
    }
    }
    Design(Matching)
    Regular expression
    

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51. デザイン(照合)
    • Mathematicaの例
    Replace[{1, {2, 3}}, (* List *)
    {a_, {b_, c_}} -> (* Pattern *)
    {a, b, c}]
    (* {1, 2, 3} *)
    Design(Matching)
    Examples of Mathematica
    

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52. デザイン(照合)
    • Mathematicaの例
    Replace[{1, 2, 3, 4, 5},
    {a___, b_, Shortest[c___]} ->
    {a}]
    (* {1, 2, 3, 4} *)
    Design(Matching)
    Examples of Mathematica
    

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53. デザイン(照合)
    • Mathematicaの例
    Replace[{1, 2, 3, 4, 5},
    {a___, b_, c___}/;b>2 ->
    {a}]
    (* {1, 2} *)
    Design(Matching)
    Examples of Mathematica
    

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54. デザイン(照合)
    • Setなどに対する照合
    match(Set[1, 2, 3]) {
    with(Set.( ??? )) { ... }
    }
    Design(Matching)
    Matching against data structures like Set
    

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55. まとめ
    • パターンマッチは非常に強力
    • ぜひ実際にコードを書いてユース
    ケースを共有してください
    Conclusions
    You know the power of pattern
    matching
    We Code.
    

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