rubyで計算機を作成する。 デザインパターンの練習。
- help <- print help strings
- help [command] <- print command howtouse
- add [number] <- AddCommand(5)
- sub [number] <- SubCommand(5)
- exec <- execute
- undo <- undo(1)
- undo [number] <-undo(number)
- cancel<- stack commands all clear
- show <- print stack commands