SICP 問題 4.40

こうゆうことでいいんだろうか？

def match( data, cond, &block)
  data.each {|x| block.call(x) if cond.call(x) }
end

data = [1,2,3,4,5]
match( data, lambda {|x| x!=5 } ) {|baker| work = data - [baker]
  match( work, lambda {|x| x!=1 }) {|cooper| work -= [cooper]
    match( work, lambda {|x| x!=1 and x!=5 and (x - cooper).abs != 1}) {|fletcher| work -= [fletcher]
      match( work, lambda {|x| x > cooper }) {|miller| work -= [miller]
        match( work, lambda {|x| (x - fletcher).abs != 1 }) {|smith|
          p [baker, cooper, fletcher, miller, smith]
        }
      }
    }
  }
}

1000回実行で0.594sec．総当りの1/100か．アルゴリズム万歳！