Roger Pack wrote::
> I really like it.
> Appears that it wants default to be level 0 [?]

Thank you for your notice.

I've change my thought.  Thread#backtrace() is more proffered name.

- On Thread#caller(lev), nobody may use lev (!= 0)
- Deciding the semantics of lev except zero may be difficult

How about it?

-- 
// SASADA Koichi at atdot dot net