程序代写代做代考 prolog Prolog 4
Prolog 4
Prolog
Some Additional Features
(Read/Write, etc.)
Fariba Sadri
• listing. Lists all user definitions
currently loaded.
• Iisting(p). Lists the definition of a given
predicate p.
In Linux to be able to use listing you must
use consult(
compile(
Input / Output
• write(T) writes a term T
• read(X) unifies with X the next term
read (the term must be followed by “.” and
carriage return if written from keyboad)
• nl writes a new line character
• tab(N) produces N tab spaces
tab may not work in some Prologs. But we
can program it easily.
tab(0).
tab(N) :- N>0, write(‘ ‘), M is N-1, tab(M).
Example
A Prolog program that writes the content of a list, one
element per line:
writelist([]).
writelist([X|L]):- write(X), nl, writelist(L).
| ?- writelist([‘Ready’, ‘Steady’, ‘Go’]).
Ready
Steady
Go
yes
Another Example
/*
A program for practising the squares of number:
• It asks the user if they want to play.
• If they do then it generates an integer at random, and
• asks them to input the square of the integer.
• If they get it right it says correct, otherwise it says wrong
and outputs the correct square.
*/
% Load the random number generator library.
% This is called a directive.
:- use_module(library(random)).
check_squares:-
nl, write(‘Do you want to play ?’),
nl, read(X),
(X=no -> (write(goodbye), nl, nl);
random(1,20,Y),
% Randomly generates an integer between 1 and 20.
nl, askabout(Y)).
random(+L, +U, -R)
unifies R with a random integer in [L,U)
when L and U are integers (note that U will
never be generated).
askabout(X):-
writeMessage([‘what is the square of’, X, ‘?’]),
read(Y),
Z is X*X,
(Y is Z -> write(correct), nl ;
write(wrong),tab(4),
writeMessage([‘the square of’, X, is, Z])),
check_squares.
Example cntd.
askabout(X):-
writeMessage([‘what is the square of’,
X, ‘?’]),
read(Y),
(Y is X*X -> write(correct), nl ;
write(wrong),nl),
check_squares.
Example cntd.
writeMessage([]).
writeMessage([X|L]):-
write(X),
write(‘ ‘),
writeMessage(L),
nl.
Comparison operators in Prolog
Comparison Definition Evaluates?
X = Y
succeeds if X and Y unify (match) in the Prolog
sense
No
X = Y
succeeds if X and Y do not unify; i.e. if not (X =
Y)
No
T1 == T2
succeeds if terms T1 and T2 are identical; e.g.
names of variables have to be the same
No
T1 == T2 succeeds if terms T1 and T2 are not identical No
E1 =:= E2
succeeds if values of expressions E1 and E2 are
equal
Yes
E1 == E2
succeeds if values of expressions E1 and E2 are
not equal
Yes
E1 < E2
succeeds if numeric value of expression E1 is <
numeric value of E2
Yes
E1 =< E2
succeeds if numeric value of expression E1 is ≤
numeric value of E2
Yes
E1 > E2
succeeds if numeric value of expression E1 is >
numeric value of E2
Yes
E1 >= E2
succeeds if numeric value of expression E1 is ≥
numeric value of E2
Yes
T1 @< T2 succeeds if T1 is alphabetically < T2 No T1 @=< T2 succeeds if T1 is alphabetically ≤ T2 No T1 @> T2 succeeds if T1 is alphabetically > T2 No
T1 @>= T2 succeeds if T1 is alphabetically ≥ T2 No
http://www.cse.unsw.edu.au/~billw/prologdict.html#is
http://www.cse.unsw.edu.au/~billw/prologdict.html#unification
http://www.cse.unsw.edu.au/~billw/prologdict.html#unification
Inserting clauses at the terminal
| ?- [user].
% consulting user …
| p(X):-q(X).
| p(X):-r(X).
| q(1).
| r(2).
| end_of_file.
% consulted user in module user, 0 msec 560 bytes
yes
| ?-
Instead of
| end_of_file.
You can type
|
How do you save the terminal
entered program to a file?
If you wish to save the program you have
entered at the terminal as a text file, you
can use the following steps:
• After the “[user].” part you have to declare
all your predicates dynamic.
• Then enter the program, ending with
end_of_file or
• Then use tell, listing, told.
Example
| ?- [user].
| dynamic(plus_one/2).
| plus_one( X, Y ) :- Y is X + 1.
| end_of_file. (or ‘
| ?- tell(yourFilename).
| ?- listing.
| ?- told.
yes
In windows use the file -> Working directory
menu to choose directory where the file
will go.
In Linux give the full file name.
Reading and writing from files
(not part of this course)
Not needed in this course.
But Prolog has a variety of predicates for
these tasks, such as:
• see(F) opens file F as the input file
• seen closes F as input file
• tell(F) opens file F as the output file
• told closes F as output file
