神奈川Ruby会議01のペアプロ問題から。 http://nabetani.sakura.ne.jp/kanagawa.rb/evalex/

evalex.rb

require 'strscan'

=begin
神奈川Ruby会議01のペアプロ問題から。 http://nabetani.sakura.ne.jp/kanagawa.rb/evalex/
ちょうど今読んでいる http://www.amazon.co.jp/Programming-Principles-Practice-Using-Edition/dp/0321992784
に電卓を作る例があったので、ほとんど写経するような形で書いてみた。
書いておきながら細かいところをちゃんと説明できないので途中まで書いていてすごく不安だった...
=end

Token = Struct.new(:kind, :string)

def tokenize(string)
  s = StringScanner.new string
  result = []
  result << get_token(s) until s.eos?
  result
end

def get_token(s)
  integer(s) || operator(s)
end

def integer(s)
  scanned_result = s.scan(/\d+/)
  return if scanned_result.nil?
  Token.new __method__, scanned_result
end

def operator(s)
  scanned_result = s.scan(/[*+&|]/)
  return if scanned_result.nil?
  Token.new __method__, scanned_result
end

# ここからリファクタリングした後のコード。今度はメソッドがでかくなり、依然として汚い。
# integerメソッドとoperatorメソッドもリファクタリングしたいけどもう疲れた...。
OPERATORS = [
  '*',
  '+',
  '&',
  '|',
]

def eval_tokens tokens, rule_id = 0
  operator = OPERATORS[rule_id]
  if operator
    left = eval_tokens(tokens, (rule_id + 1))
    token = tokens.shift
    until token.nil?
      if token.string == operator
        left = left.__send__ operator, eval_tokens(tokens, (rule_id + 1))
        token = tokens.shift
      else
        tokens.unshift token
        return left
      end
    end
    return left
  else
    token = tokens.shift
    if token.kind == :integer
      return token.string.to_i
    else
      raise 'error'
    end
  end
end
# ここまでリファクタリングした後のコード。

TEST_CASES = [
  # [ id, input, expected ],
  [ 0, "4*5+6&7|8", "44" ],    
  [ 1, "15*5", "75" ],    
  [ 2, "15+5", "20" ],    
  [ 3, "15&5", "5" ],    
  [ 4, "15|5", "15" ],    
  [ 5, "30*15*5", "2250" ],    
  [ 6, "30*15+5", "600" ],    
  [ 7, "30*15&5", "150" ],    
  [ 8, "30*15|5", "450" ],    
  [ 9, "30+15*5", "225" ],    
  [ 10, "30+15+5", "50" ],    
  [ 11, "30+15&5", "35" ],    
  [ 12, "30+15|5", "45" ],    
  [ 13, "30&15*5", "70" ],    
  [ 14, "30&15+5", "19" ],    
  [ 15, "30&15&5", "4" ],    
  [ 16, "30&15|5", "14" ],    
  [ 17, "30|15*5", "155" ],    
  [ 18, "30|15+5", "36" ],    
  [ 19, "30|15&5", "5" ],    
  [ 20, "30|15|5", "31" ],    
  [ 21, "1+2+3+4+5+6+7+8+9+10", "55" ],    
  [ 22, "1*2*3*4*5*6*7*8*9*10", "3628800" ],    
  [ 23, "1+2+3+4+5*6+7+8+9+10", "600" ],    
  [ 24, "1*2*3*4*5+6*7*8*9*10", "1330560" ],    
  [ 25, "1|2|4|8|16|32|64|128|256|512", "1023" ],    
  [ 26, "2046&2045&2043&2039&2031&2015&1983&1919&1791&1535", "1024" ],    
  [ 27, "0+1|7*6", "42" ],    
  [ 28, "6|4+2&9+4", "10" ],    
  [ 29, "0&6+1&6|4*2", "0" ],    
  [ 30, "4|4*7+7+4&9", "56" ],    
  [ 31, "9&8*2+3*1|2|7", "280" ],    
  [ 32, "230+83*751&176", "50080" ],    
  [ 33, "89+62465*94&84", "5254536" ],    
  [ 34, "668&925+398*562", "599092" ],    
  [ 35, "15|9+348*302&23&77", "1452" ],    
  [ 36, "3&3&6|7+3|5*3|2&4*4", "0" ],    
  [ 37, "7*6|7|7*1&7|7&3&8*3", "0" ],    
  [ 38, "896+316*209*264&728", "2026464" ],    
  [ 39, "1844+41*64|7906|66842", "138965970" ],    
  [ 40, "2&41&6884*69857+68083", "0" ],    
  [ 41, "2+3*9*3|6|7&0+3+3*6&8", "0" ],    
  [ 42, "895+400*988|549&237+488", "938875" ],    
  [ 43, "30*48&99036+140&33+75|645", "22050" ],    
  [ 44, "278+2033+53*96*56|3303|3&14", "3177216" ],    
  [ 45, "5380&27|643*2+1888&74+30|16", "0" ],    
  [ 46, "0&3845+6645*4293+78&78*3102|9|3", "90127550385" ],    
  [ 47, "78&44956&67*974|413+13237*5588|54*668", "0" ],    
  [ 48, "500*206+145|167|163|465&668+662+806*681&458", "123896000" ],    
  [ 49, "82+14&0*344+34+542916&18*11|844|64*873223|840993", "23813260003764" ],    
  [ 50, "374958|6727+53965&53*954&29|6*138572+59|547783&43*8998", "12178274756590800" ],    
]

def test
  failures = TEST_CASES.select {|_id, input, expected| eval_tokens(tokenize(input)) != expected.to_i }
  if failures.empty?
    puts "All OK"
  else
    failures.each do|id, input, expected|
      puts "#{id}: NG!: actual: #{actual}, expected: #{expected}"
    end
  end
end

# ここからリファクタリングする前のコード。超コピペだらけ。

def ex1 tokens
  left = ex2(tokens)
  token = tokens.shift
  until token.nil? do
    case token.string
    when '*'
      left *= ex2(tokens)
      token = tokens.shift
    else
      tokens.unshift token
      return left
    end
  end
  return left
end

def ex2 tokens
  left = ex3(tokens)
  token = tokens.shift
  until token.nil? do
    case token.string
    when '+'
      left += ex3(tokens)
      token = tokens.shift
    else
      tokens.unshift token
      return left
    end
  end
  return left
end

def ex3 tokens
  left = ex4(tokens)
  token = tokens.shift
  until token.nil? do
    case token.string
    when '&'
      left &= ex4(tokens)
      token = tokens.shift
    else
      tokens.unshift token
      return left
    end
  end
  return left
end

def ex4 tokens
  left = ex5(tokens)
  token = tokens.shift
  until token.nil? do
    case token.string
    when '|'
      left |= ex5(tokens)
      token = tokens.shift
    else
      tokens.unshift token
      return left
    end
  end
  return left
end

def ex5 tokens
  token = tokens.shift
  if token.kind == :integer
    token.string.to_i
  else
    raise 'error'
  end
end