1. CSC 8520 Spring 2013. Paula Matuszek
Lab Exercise 1
On the syllabus page there are links to two Prolog programs: a simple Prolog planner and an ADT library.
Download them and consult planner.pl, which will in turn consult adts.pl.
?- consult('planner.pl').
% adts compiled 0.00 sec, 6,364 bytes
% planner.pl compiled 0.00 sec, 11,456 bytes
true.
CSC 8520 Spring Paula Matuszek

2. CSC 8520 Spring 2013. Paula Matuszek
Test that it is working by typing “test.” at the prompt.
You should get a list of moves.
?- test.
moves are
pickup(a)
putdown(a)
pickup(b)
stack(b, c)
stack(a, b)
true. ?-
CSC 8520 Spring Paula Matuszek

3. CSC 8520 Spring 2013. Paula Matuszek
Planner
Planner is a very simple Prolog implementation of a planner using a STRIPS-like notation.
A state is a list of conditions.
A problem has an initial state and a goal state. For instance:
the initial state for a blocks world might be:
[handempty, ontable(b), ontable(c), on(a, b), clear(c), clear(a)]
the goal state for the blocks world might be: [handempty, ontable(c), on(a,b), on(b, c), clear(a)]
CSC 8520 Spring Paula Matuszek

4. CSC 8520 Spring 2013. Paula Matuszek
Moves
A move is an action, consisting of a name, a list of preconditions, and an effect list of changes.
Moves are included in the Prolog file.
For example:
move(pickup(X), % move name
[handempty, clear(X), on(X, Y)], % preconditions
[del(handempty), del(clear(X)), % list of conditions
del(on(X, Y)), add(clear(Y)), % to be added and
add(holding(X))]) % deleted
CSC 8520 Spring Paula Matuszek

5. CSC 8520 Spring 2013. Paula Matuszek
plan
plan takes a current state, a goal state, a list of states which have already been reached (Been_list), and a list of moves which have already been carried out. It then
checks to see if the current state = goal state. If so, print out list of moves.
finds an applicable move
does the adds and deletes
checks to be sure we haven’t already been there
adds the current state to the list of states and the current move to the list of moves
recurs.
CSC 8520 Spring Paula Matuszek

6. CSC 8520 Spring 2013. Paula Matuszek
Running it
go takes an initial state and a goal state
it invokes plan with
current state = initial state
goal state = goal state
Been_list = initial state
Moves list empty.
test is just there to give a way to test it, using the blocks world.
CSC 8520 Spring Paula Matuszek 6

7. CSC 8520 Spring 2013. Paula Matuszek
Spare tire problem
Problem: you have a flat. Develop a plan to fix it.
Initial condition is that the flat is on the axle and the spare is in the trunk.
Goal condition is that the flat is in the trunk and the spare is on the axle.
Some possible actions include removing something from something, installing something in something.
Some possible conditions include at(a,b) and clear(axle)
CSC 8520 Spring Paula Matuszek

8. CSC 8520 Spring 2013. Paula Matuszek
Lab exercise 2.
Develop the appropriate initial state, goal state and move definitions for the Spare Tire Problem.
Add to planner.pl your moves and a new predicate test2 which solves this problem.
CSC 8520 Spring Paula Matuszek