face-to-face grading project 3
difficulty level: 3/5
approxmite time: 30 minutes
maximum time: 45 minutes

create two places with no exit, namely heaven and hell.

property means using table, not a method
modify the person class that it has a proerty call good?, which only has two 
values, #t or #f. when instantiate a new person, do the following:
(define object_name (instantiate person 'name place 'good_or_not))

example:
(define hacker (instantiate person 'hacker 61A-lab 'good))
then (ask hacker 'good?) will give #t
(define jj (instantiate person 'jj 61A-lab 'any_thing_not_good))
then (ask jj 'good?) will give #f

add one method name lose_strength to person class. it takes one arguement.
(ask hacker 'lose_strength 50) will decrease hacker's strength by 50

notes:
thief class will be default to #f
police class will be default to #t or #f randomly
angel class will be default to #t (see below)
thus, the way to istantiate these three child class will remain the same

(define simon (instantiate person 'simon 61a-lab 'good))
(define nasty (instantiate thief 'nasty 61a-lab))
(define cop (instantiate police 'cop 61a-lab))
(define hong (instantiate angel 'hongzi soda))

creat a child class of person, named angel, has ability describled below:

when angel enter a place (modify the go method)
1) check everyone in the current place, if strength > 0, do nothing
2) if stength <= 0, check the good? part of that person
3) good? #t will ask the person go-directly-to heaven
4) good? #f will ask the person go-directly-to hell

extra for experts:
5) make the person loose all the things first,
   then go to heaven or hell.
6) add a method salvation to angel class, which take a person as argument.
   (ask angel_object 'savlvation target_person) will change target_person's
   good? proverty to #t
   example:
   (ask hong 'salvation nasty) will change nasty's good? to #t
   (ask hong 'salvation simon) will not change anything.

first drop simon, nasty, cop's strength to 0 or less
show that you can move hong around and place simon, cop to heaven or hell, 
while place nasty to hell.

if you get the extra for experts on time, you can ask 0.5 points back on 
any homework you lost points before, but if you get full credit for all 
the homeworks, nothing can be changed.


end of face-to-face grading project 3