improve traverse operation, use applicative
improve traverse operation, use applicative

Ignore-this: 88d9480b322d4d6f2f21ef6b6f69f203

darcs-hash:20140512060226-1a7c6-b6223d5107f3704735b209f2e92351506ac2c322

jimcrayne/jhc,jimcrayne/jhc,jimcrayne/jhc,jimcrayne/jhc