DecoratorOf given function.

Do create a FunctionRunner with first function f.

DoCase and stop.

DoIf and stop.

Decorator for function.

Function would be invoked in waterfall one by one if the last output is error, function runner would halt right now.

FunctionRunner execute functions one by one.

AlwaysFunction would be invoked at last.

ConditionFuntion execute when condition.

ErrorFunction would be invoked when err occurs.