PA4 : first import
all classes node are Class, add get_parent/get_name to get its symbol
look up all user defined classess and create its relation map
add language pre-defined class and enhane error message
add inheritance checking
add cyclie, undefined parent check
enhance error msg
tmp
get all id information
tmp2
check nomain error
mess
first typechecking
enhance object
enhance new
enhance let_class
enhance type_class
enhance loop
enhance static/dynamic function