Assignment 4
Due 5:00 PM, Tuesday, Dec. 4th
Department of Computer Science
| |
Assignment 4 Due 5:00 PM, Tuesday, Dec. 4th Department of Computer Science | |
The purpose of this assignment is to show you how to interact
with our Prolog environment, xsb, and to get a little experience
in writing Prolog programs.
First, download the file initprolog.P to
your working directory.
This file defines a vi and an
emacs relation. Think of these as commands for editting a
file. Upon exiting from the editting session, the file is consulted
(meaning the definitions are compiled and loaded into Prolog).
Then, on any of Solaris machines type
xsb and load the editting relations.
Here's what you should see:
-> xsb [xsb_configuration loaded] [sysinitrc loaded] [packaging loaded] XSB Version 2.2 (Tsingtao) of April 20, 2000 [sparc-sun-solaris2.8; mode: optimal; engine: chat; scheduling: batched] | ?- [initprolog]. [Compiling ./initprolog] [initprolog compiled, cpu time used: 0.0500 seconds] [initprolog loaded] yes | ?-This compiles the
initprolog.P file, producing
initprolog.O. The next time you load this file,
you will only see
| ?- [initprolog]. [initprolog loaded] yes | ?-because the file was already compiled.
This is the contents of the initprolog.P file:
append([],L,L).
append([X|L1],L2,[X|L3]) :- append(L1, L2, L3).
vi(File) :-
name(vi,V),
name(File,FileString),
append(V,[32|FileString],CommandString),
name(Command,CommandString),
unix(Command),
consult(File).
emacs(File) :-
name(emacs,V),
name(File,FileString),
append(V,[32|FileString],CommandString),
name(Command,CommandString),
unix(Command),
consult(File).
To edit a file, say it is called try.P, do
| ?- emacs('try.P').
Emacs will be started, or vi if you use vi('try.P')., on the file
that you name. When you save and quit the editor, you will see
[Compiling ./try] [try compiled, cpu time used: 0.028999 seconds] [try loaded] yesYou see that your file as automatically compiled and loaded for you. An easy way to add new assertions while
xsb is running, is to
type [user]. For example,
| ?- [user]. [Compiling user] ff. [user compiled, cpu time used: 0.019997 seconds] [user loaded] yes | ?- ff. yesWhen finished, you may exit the Prolog environment by typing control-d.
Type the following definition for the relation gcd/3 into a
file named gcd using an editting relation (like
emacs('gcd.P').). When you save the file and exit the editting
session, your relations will be consulted. If you get syntax errors,
edit the file again and fix them.
gcd(X,X,X).
gcd(X,Y,D) :-
X < Y,
Y1 is Y-X,
gcd(X,Y1,D).
gcd(X,Y,D) :-
Y < X,
gcd(Y,X,D).
Test this by finding the greatest common divisors for five different
pairs of integers (like gcd(16,160,D).).
Watch the execution of gcd/3 using the trace/0
relation. You may type h while tracing to see the available
commands. Just pressing return will take a single step. notrace. will turn off tracing.
For example:
| ?- trace. yes [trace] | ?- gcd(5,20,D). (0) Call: gcd(5,20,_10003020) ? (1) Call: gcd(5,15,_10003164) ? (2) Call: gcd(5,10,_10003192) ? (3) Call: gcd(5,5,_10003220) ? (3) Exit: gcd(5,5,5) ? (2) Exit: gcd(5,10,5) ? (1) Exit: gcd(5,15,5) ? (0) Exit: gcd(5,20,5) ? D = 5 yes [trace] | ?-
Now try a floating point number as an argument. Be sure you have
called the trace. relation first. Explain the result you
see to yourself. (You don't have to turn your explanation in.)
gcdgcd/3 relation
that catches such incorrect arguments so you can exit when non-integer
arguments are detected. You may use the not operator,
the integer(X) relation, which succeeds if X
is an integer, the cut operator !, and the term
fail. Place the additional rule in the right place in
your gcd.P file. The additional rule should catch
non-integer arguments and fail immediately.
You must start by
typing a prolog file defining the relations needed to represent all of
the dependencies in the prerequisites chart. Call that file
prereqs.P Then, write a second file named
taken.P that contains
assertions for the courses you have taken so far. Warning: you should
define all assertions with consequents containing a particular
relation, like taken, in the same file.
Once both of these files are loaded in xsb, you should
be able to get the correct yes or no answer to the queries
taken(cs301). and cantake(cs440). or for any
other query using the same relation for courses at and below the 400
level. Once this is working, you can collect a set of all courses you
have taken so far by doing setof(X,taken(X),L). and you
can find out all courses you are qualified to take by doing
setof(X,cantake(X),L). Also, define the relation
deficiencies that determines the set of all courses you
have not taken that must be taken before a given course. For example,
if you have only taken m160, you will see this:
| ?- deficiencies(cs301,X). X = [cs153,cs166,cs200,m121,m124,m161,m229] yes
For purposes of grading, build your "courses taken" file to show that you have taken all courses at the 300 level and below, except CS370, ST301. If you have written the prolog correctly in both files, you should see this result:
-> xsb [xsb_configuration loaded] [sysinitrc loaded] [packaging loaded] XSB Version 2.2 (Tsingtao) of April 20, 2000 [sparc-sun-solaris2.8; mode: optimal; engine: chat; scheduling: batched] | ?- [prereqs]. [prereqs loaded] yes | ?- [taken]. [taken loaded] yes | ?- cantake(cs440). yes | ?- cantake(cs470). no. | ?- cantake(cs370). no. | ?- setof(X,cantake(X),L). X = _h72 L = [cs153,cs166,cs200,cs253,cs270,cs301,cs314,cs410,cs414,cs420,cs430,cs440,cs453,cs486,cs495,m121,m124,m160,m161,m229,st301] yes | ?- deficiencies(cs370,L). L = [st301] yes | ?- deficiencies(cs470,L). L = [cs370,st301] yes | ?- deficiencies(cs440,L). no
tar cvf assign4.tar gcd.P prereqs.P taken.PThen simply run our checkin command as you have done before to check in
assign4.tar.