change private and add @tailrec

Signed-off-by: noboru kudoh <noboru.kudoh@gmail.com>
 add dependency scala-arms

Signed-off-by: noboru kudoh <noboru.kudoh@gmail.com>
 remove console output

Signed-off-by: noboru kudoh <noboru.kudoh@gmail.com>
 introduce implicit parameter for callback

Signed-off-by: noboru kudoh <noboru.kudoh@gmail.com>
 add dependencies for specs2

Signed-off-by: noboru kudoh <noboru.kudoh@gmail.com>
 add Evaluator utility for user input callback method

Signed-off-by: noboru kudoh <noboru.kudoh@gmail.com>