[ruby-dev:38085] Re: [Feature:trunk] nested loop construct

Yukihiro Matsumoto wrote::
> def nloop(*args, &block)
>   helper = ->(args, buf, offset, block) {
>     limit = args[offset]
>     if (offset+1 == args.size)
>       limit.times do|i|
>         buf[offset] = i
>         block.yield *buf
>       end
>     else
>       limit.times do|i|
>         buf[offset] = i
>         helper.(args, buf, offset+1, block)
>       end
>     end
>   }
>   helper.(args, [], 0, block)
> end

　うわー，はじめてみました． -> とか .() とか．


def nloop *args
  str = ''
  h = lambda{|i|
    next "yield #{(0...i).map{|e| "v#{e}"}.join(', ')}\n" \
    if args.length == 0

    str << "v#{i} = 0; while v#{i} < #{args.shift}\n"
    str << h.call(i+1)
    str << "v#{i} = v#{i}.succ;end\n"
    ''
  }
  h.call(0)
  eval(str)
end

require 'benchmark'
max = 10000
Benchmark.bm{|x|
  x.report{
    max.times{|i|
      max.times{|j|
      }
    }
  }
  x.report{
    nloop(max, max){|i, j|
    }
  }
}


ruby 1.9.1p0 (2009-02-02 revision 21960) [i386-mswin32_90]
t.rb:12: warning: useless use of a variable in void context
      user     system      total        real
 15.039000   0.000000  15.039000 ( 13.957000)
 12.105000   0.031000  12.136000 ( 11.492000)


ruby 1.8.7 (2008-12-11 revision 20371) [i386-mswin32_90]
t.rb:12: warning: useless use of a variable in void context
      user     system      total        real
 10.671000   0.016000  10.687000 ( 10.642000)
t.rb:13:in `nloop': (eval):3:in `nloop': no block given (LocalJumpError)
	from t.rb:26:in `eval'
	from t.rb:13:in `nloop'
	from t.rb:26
	from c:/tmp/ruby_1_8/lib/ruby/1.8/benchmark.rb:293:in `measure'
	from c:/tmp/ruby_1_8/lib/ruby/1.8/benchmark.rb:380:in `report'
	from t.rb:25
	from c:/tmp/ruby_1_8/lib/ruby/1.8/benchmark.rb:177:in `benchmark'
	from c:/tmp/ruby_1_8/lib/ruby/1.8/benchmark.rb:207:in `bm'
	from t.rb:18


1. あれー，1.8.7 のほうが times{times{}} が速い　なんでー？
2. eval() の中から yield 出来ないんだっけ？


Debian etch/amd64

ruby 1.9.2dev (2009-02-26 trunk 22636) [x86_64-linux]
      user     system      total        real
  7.840000   0.000000   7.840000 (  7.836987)
  7.900000   0.000000   7.900000 (  7.900081)

ruby 1.8.5 (2006-08-25) [x86_64-linux]
      user     system      total        real
 30.340000  12.900000  43.240000 ( 43.247637)
../trunk/test.rb:8:in `<<': can't convert nil into String (TypeError)
        from ../trunk/test.rb:8:in `nloop'
        from ../trunk/test.rb:8:in `call'
        from ../trunk/test.rb:8:in `nloop'
        from ../trunk/test.rb:12:in `call'
        from ../trunk/test.rb:12:in `nloop'
        from ../trunk/test.rb:26
        from /usr/lib/ruby/1.8/benchmark.rb:293:in `measure'
        from /usr/lib/ruby/1.8/benchmark.rb:377:in `report'
        from ../trunk/test.rb:25
        from /usr/lib/ruby/1.8/benchmark.rb:177:in `benchmark'
        from /usr/lib/ruby/1.8/benchmark.rb:207:in `bm'
        from ../trunk/test.rb:18

3. 1.9 でも times{times{}} のほうが速い−．なんでー？
4. 1.8.7 とバックトレースが違う−．

-- 
// SASADA Koichi at atdot dot net