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Revision at the Beginning of the 2 nd Semester (repeated slides)

Revision at the Beginning of the 2 nd Semester (repeated slides). Small Coursework (40%) – Please complete it asap Go to: http://www.cems.uwe.ac.uk/~ryang/prolog/top.html Week 2 ( simp + cango2) Week 3 (cango3 +cango4) Week 4 (subset + nth_item ) Week 5 (shift + cal_route ).

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Revision at the Beginning of the 2 nd Semester (repeated slides)

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  1. Revision at the Beginning of the 2nd Semester (repeated slides) Small Coursework (40%) – Please complete it asap Go to: http://www.cems.uwe.ac.uk/~ryang/prolog/top.html Week 2 (simp + cango2) Week 3 (cango3 +cango4) Week 4 (subset + nth_item) Week 5 (shift + cal_route)

  2. In the original program, the relation arrow(X,Y) represents a directed link from X to Y. The relation cango(X,Y) means that there is a path from X to Y cango(X, Y):- %% base arrow(X, Y). cango(X, Y):- %% recursion arrow(X, Z), cango(Z, Y). % another example: ancestor(X, Y):-% base parent(X, Y). ancestor(X, Y):-% recursion parent(X, Z), ancestor(Z, Y). You must fully understand this program!(what, why, how) also its extensions (how to use lists) b a d c e f g h An ancestor is a parent or (recursively) the parent of an ancestor  - from wiki

  3. cango(X, Y):- arrow(X, Y). cango(X, Y):- arrow(X, Z), cango(Z, Y). ?- cango(a,h). a b c e d f d g g f h hhhhh Prolog uses ‘cango’ with a depth first search. ‘cango’ is a general program not just for this given cube. How does ‘cango’ program work? b a d c e f g h Observation: change the order of arrow, then check if the order of solutions changes

  4. In the original program, the relation arrow(X,Y) only represents a link from X to Y, not Y to X. How do we extend it to a bi-directional link? Easy – using disjunction: next(X, Y):- arrow(X, Y). next(X, Y):- arrow(Y, X). Is ‘cango’ really a general program? b a d c e f g h cango(X, Y):- next(X, Y). cango(X, Y):- next(X, Z), cango(Z, Y).

  5. Introduced circles into the map. There is a danger of being trapped in a circle! ?- cango(a,h). a b c e a d b c a a What happens after replacing ‘arrow’ by ‘next’? b a d c e f g h cango(X, Y):- next(X, Y). cango(X, Y):- next(X, Z), cango(Z, Y).

  6. We must add something to avoid being trapped in a circle. Solution 1: using an extra list to store the path generated so far, only extend a new node which is not in the list Solution 2: no u-turn. it is restricted to certain type of maps where circles are only created by u-turn. Q: Is ‘cango’ a general program? A: It only works if no circle in the map. b a d c e f g h Q-block

  7. Solution 2 (we will use this!) • For some maps, there are no circles as long as u-turn is not allowed. In this case, the easy solution is to add an extra test to disallow u-turn. next(a, b, north). next(b, a, south). ...... % PreDir is the direction before X cango(X,Y, PreDir):- next(X,Y, Dir), not_u_turn(PreDir, Dir). cango(X,Y, PreDir):- next(X,Z, Dir), not_u_turn(PreDir, Dir), cango(Z , Y, Dir).

  8. Two ways to define not_u_turn • Define ‘u_turn’, then make use of \+ (not) : u_turn(south,north). u_turn(north,south). u_turn(west,east). u_turn(east, west). not_u_turn(X,Y): - \+( u_turn(X,Y) ). • Define ‘not_u_turn’ directly : not_u_turn(south, west). not_u_turn(south, east). ....... not_u_turn(start, _).

  9. Move to real program, more information needed in the ‘next’ % (From,To, Direction, WhichSide, Distance) next('2q43', '2q49', south, right, 1). next('2q49', '2q43', north, left, 1). next('2q49', 'area3', south, left, 1). next('area3', '2q49', north, left, 1). next('area3', '2q46', south, left, 3). next('2q46', 'area3', north, right, 3). next('2q46', '2q47', south, left, 2). next('2q47', '2q46', north, right, 2). .......

  10. Your ‘cango’ program should have6 parameters cango(X,Y,Path,Dir,Dist,PreDir) Path and Dir are lists which are exactly same as cango4 Dist is a list of distances PreDir indicates previous direction. You need to use it to compare with the next direction. no u-turn ! For example ?- cango(‘2q43’, ‘2q47’, P, Dir, Dist, start). P = [2q43,2q49,area3,2q46,2q47] Dir = [south,south,south,south] Dist = [1,1,3,2]

  11. Put them all together :-[map]. % include the file map.pl test(X, Y):- cango(X, Y, Path, Dir, Dist, start), cal_route(Dir, Dist, NewDir, NewDist), write(NewDir), nl, write(NewDist), nl.

  12. A little help on ‘cal_route’ (week5’s task) • The following program reduces a sequence of same items into to one item reduce([X],[X]). % if only one item % nothing to reduce reduce([X,X|T], R):- reduce( [X|T], R ). reduce([X,Y|T], [X|R]):- X \== Y, reduce( [Y|T], R ). ?- reduce([a,a,b,b,b,c], R). produces R = [a,b,c]

  13. Start to work on chatbot You need to copy three files: • map.pl http://www.cems.uwe.ac.uk/~ryang/prolog/code/map.pl • A dummy chatbothttp://www.cems.uwe.ac.uk/~ryang/prolog/code/chat.pl • Something for reading input http://www.cems.uwe.ac.uk/~ryang/prolog/code/readin.pl

  14. chatbot:- print_welcome, conversations. conversations:- repeat, % prolog built-in print_prompt(you), readin(S), % defined in file % readin.pl gen_reply(S,R), print_prompt(me), write_list(R), is_quit(S). is_quit(S):- member(bye, S). gen_reply(S, R):- % totally random respones_db(random, Res), % create a random number length(Res, Length), Upper is Length+1, random(1, Upper, Rand), nth_item(Res, Rand, R). respones_db(random, [ [hello, '!'], [hi, there , '.', this, is, not, a, hello_world, program, '!'], [it, is, a, nice, day, '.'], [have, you, talked, to, me, before, '?'], ['.', '.', '.', what, do, you, mean, '?'] ]). A Simple Chatbot – only producing random responses

  15. | ?- chat. Welcome! I am a chatbot Please finish your line with a full stop, ?, or ! user Hi. bot1 : hello ! user |: what is your name? bot1 : have you talked to me before ? user |: no, I don't think so. bot1 : hi there . this is not a hello_world program ! user |: cool. bot1 : sorry , i am only a single minded chatbot . user |: ok, i don't mind. bot1 : . . . what do you mean ? user |: I mean I like you. (cont.) | bot1 : sorry i cannot remember everything you said . user |: ok. bot1 : sorry , i am only a single minded chatbot . user |: you said that. bot1 : sorry i cannot remember everything you said . user |: no problem. bot1 : oh ...... ok user |: good. bot1 : can you say it again ? user |: good!!!! bot1 : have you talked to me before ? user |: getting boring now, bye. bot1 : bye !

  16. After Copying chat.pl, you need to add your ‘subset’, ‘nth_item’, and the following ‘write_list’ - Output a list - The following program prints out elements in a list and puts one space between them. write_list([]):- nl. %% print a new line write_list([H|T]):- write(H), write(‘ ‘), write_list(T).

  17. A simple way to link chatbot to ‘cango’ program • In get_reply(S,R) check if S has a pattern ‘to ... from ...’ if yes, call your ‘cango’, then generate the reply. pattern_tofm([to, X, from, Y|_], X, Y). % yes! pattern_tofm([_|T], X, Y):- % carry on checking pattern_tofm(T, X, Y).

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