irb(main):001:0> RUBY_DESCRIPTION => "ruby 2.1.0dev (2013-08-01 trunk 42311) [x86_64-darwin12.4.0]" irb(main):002:0> 1/3r => (1/3) irb(main):003:0> 1+2i => (1+2i) irb(main):004:0> 0.5r => (1/2) irb(main):005:0> 便利になったね〜♪ 参考: http…