init commit of source code.
generic release 20130521
a bookmark version
revision-20130602
revision-20130602
revised local-replacing
removed type_name/path
removed impls/enables/disables
revised object model
revised class model
revised some comments
revised some comments
adjusted comparing logic;inserted some implementations.
removed explicit local-replacing operation.
implemented filter.
implemented converter.
implemented \cons'
add a conversion logic to iterator.
add a clear method.
implemented is_empty & not_empty