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I'm currently learning Prolog and I want to create a specific rule which will check if a person can watch a film. The condition for true should be age of person equal of higher than required age for film.
So I have something like that:
person("John",19).
person("Kate",14).
person("Carl",8).
film("Shining",18,"Horror").
film("Little Agents",13,"Family").
film("Frozen",7,"Animation").
can_borrow(film(_,Age1,_),person(_,Age2)):-Age2>=Age1.
And if I ask i.e.
?- can_borrow(film("Shining",18,"Horror"),person("John",19)).
It works and returns true.
But when I ask to show me all possible combinations (all films which every person can watch)
?- can_borrow(X,Y).
I have an error:
ERROR: Arguments are not sufficiently instantiated
How to write the rule properly, so it would work as I've written above?
Thanks in advance.
The film(_, Age1, _) and person(_, Age2) in can_borrow(film(_, Age1, _), person(_, Age2)) are just terms with a functor that happens to be the same as a predicate. But Prolog does not attach special meanings to it. You should here call predicates to unify the terms. For example:
can_borrow(film(Title, Age1, Genre), person(Name, Age2)) :-
film(Title, Age1, Genre),
person(Name, Age2),
Age1 =< Age2.
another way to ask the question is:
How I can list all the properties of an atom?
For example:
movie(agora).
director(agora, 'Alejandro Amenabar')
duration(agora, '2h').
so, I will like to receive all the predicates that has agora for argument. In this case it will be: movie, director, duration, with the other parameters ('Alejandro Amenabar', '2h').
I found: this, and this questions, but I couldn't understand well.
I want to have the value of false in the "variable Answer" if PersonInvited doesn't like something about the movie.
My query will be:
answer(Answer, PersonInvited, PersonWhoMadeInvitation, Movie)
Answer: I don't like this director
answer(false, PersonInvited, PersonWhoMadeInvitation, Movie):-
director(Movie, DirectorName),not(like(PersonInvited,DirectorName)).
The same thing will happen with any property like genre, for example.
Answer: I don't like this genre
answer(false, PersonInvited, PersonWhoMadeInvitation, Movie):-
genre(Movie, Genre), not(like(PersonInvited,Genre)).
So, I want to generalize this situation, instead of writing repeatedly every feature of every object.
I found two solutions the 2nd is cleaner from my point of view, but they are different.
Parameters:
PredName: Name of the predicate.
Arity: The Arity of the Predicate.
ParamValue: If I want to filter by one specific parameter.
PosParam: Which is the position of the parameter in the predicate.
ListParam: All the value of the posibles values parameters (mustbe a Variable all the time).
Solution 1:
filter_predicate(PredName, Arity, ParamValue,PosParam, ListParam):-
current_predicate(PredName/Arity),
Arity >= PosParam,
nth(PosParam, ListParam, ParamValue),
append([PredName], ListParam, PredList),
GlobalArity is Arity + 1,
length(PredList, GlobalArity),
Predicate =.. PredList,
Predicate.
Query
filter_predicate(PredName, Arity, agora, 1, Pm).
Output
Arity = 2
Pm = [agora,'Alejandro Amenabar']
PredName = director ?
yes
Solution2:
filter_predicate(PredName, Arity, ParamList):-
current_predicate(PredName/Arity),
append([PredName], ParamList, PredList),
GlobalArity is Arity + 1,
length(PredList, GlobalArity),
Predicate =.. PredList,
Predicate.
Query 1:
filter_predicate(PredName, Arity, [agora, X]).
Output
Arity = 2
PredName = director
X = 'Alejandro Amenabar' ?
Query 2:
filter_predicate(PredName, Arity, [X, 'Alejandro Amenabar']).
Output
Arity = 2
PredName = director
X = agora ?
here is my attempt, using SWI-Prolog
?- current_predicate(so:F/N), N>0, length(As,N), Head =.. [F|As], clause(so:Head,Body), As=[A|_], A==agora.
note that I coded into a module called so the facts, so I qualify with the module name the relevant calls. Such builtins (clause/2 and current_predicate/1) are ISO compliant, while modules (in SWI-prolog) are not. So I'm not sure about portability, etc...
clause/2 it's a builtin that allows for easy writing metainterprets. See the link for an awesome introduction to this Prolog historical 'point of strength'.
The 2 last calls (I mean, As=[A|_], A==agora) avoid matching clauses having a variable as first argument.
Using reading lines into lists with prolog
All your predicates are in a file 'my_file.pl'.
e.g. my_file.pl contains:
movie(agora).
director(agora, 'Alejandro Amenabar').
duration(agora, '2h').
You can use:
getLines(File,L):-
setup_call_cleanup(
open(File, read, In),
readData(In, L),
close(In)
).
readData(In, L):-
read_term(In, H, []),
( H == end_of_file
-> L = []
; L = [H|T],
readData(In,T)
).
pred_arg_file(Pred,Argue,File):-
getLines(File,L),
member(M,L),
M=..List,
member(Argue,List),
List=[Pred|_].
Then you can query:
?-pred_arg_file(Pred,agora,'my_file.pl').
Pred = movie ;
Pred = director ;
Pred = duration ;
false
or
?- findall(Pred,pred_arg_file(Pred,agora,'my_file.pl'),Preds).
Preds = [movie,director,duration].
If you want to return the properties, return the whole List not just the head.
pred_arg_file(List,Argue,File):-
getLines(File,L),
member(M,L),
M=..List,
member(Argue,List).
From my understanding you should change your data representation so that you can query the relations.As other answers have pointed out, So use triples, you can easily write code to change all your relations into this form as a one off. You then need to work out what the best way to store likes or dislikes are. This will effect how negation works. In this example:
relation(starwars,is,movie).
relation(lucas, directs,starwars).
relation(agora, is,movie).
relation('Alejandro Amenabar', directs, agora).
relation(agora, duration, '2h').
like(ma,'Alejandro Amenabar').
like(ma,movie).
like(ma,'2h').
ma_does_not_want_to_go(Film):-
relation(Film,is,movie),
relation(Film,_,Test), \+like(ma,Test).
ma_does_not_want_to_go(Film):-
relation(Film,is,movie),
relation(Test,_,Film), \+like(ma,Test).
ma_wants_to_go(Film):-
relation(Film,is,movie),
\+ma_does_not_want_to_go(Film).
sa_invites_ma(Film,true):-
ma_wants_to_go(Film).
sa_invites_ma(Film,false):-
ma_does_not_want_to_go(Film).
A draft of a solution using Logtalk with GNU Prolog as the backend compiler:
% a movie protocol
:- protocol(movie).
:- public([
director/1,
duration/1,
genre/1
]).
:- end_protocol.
% a real movie
:- object('Agora',
implements(movie)).
director('Alejandro Amenabar').
duration(120).
genre(drama).
:- end_object.
% another real movie
:- object('The Terminator',
implements(movie)).
director('James Cameron').
duration(112).
genre(syfy).
:- end_object.
% a prototype person
:- object(person).
:- public([
likes_director/1,
likes_genre/1
]).
:- public(likes/1).
likes(Movie) :-
conforms_to_protocol(Movie, movie),
( Movie::genre(Genre),
::likes_genre(Genre) ->
true
; Movie::director(Director),
::likes_director(Director) ->
true
; fail
).
:- end_object.
% a real person
:- object(mauricio,
extends(person)).
likes_director('Ridlye Scott').
likes_genre(drama).
likes_genre(syfy).
:- end_object.
Some sample queries:
$ gplgt
...
| ?- {movies}.
...
(5 ms) yes
| ?- mauricio::likes('Agora').
true ?
yes
| ?- mauricio::likes(Movie).
Movie = 'Agora' ? ;
Movie = 'The Terminator' ? ;
no
| ?- 'The Terminator'::director(Director).
Director = 'James Cameron'
yes
The code can be improved in several ways but it should be enough to give you a clear idea to evaluate this solution.
If I understood your question properly I propose the follow:
What if you change your schema or following this idea you can make a method that simulate the same thing.
class(movie, agora).
property(director, agora, 'Alejandro Amenabar').
property(duration, agora, '2h').
If do you want the types of agora, the query will be:
class(Type, agora)
If you want all the properties of agora, that will be:
property( PropertyName, agora, Value).
I'm writing a function called leagalCourse, it takes just one parameter, a course list. A course like, for example, john+mary+94 would represent a project done by John and Mary with a mark of 94.
It should be true if the course data is “legal”, which means that it must not have a project with the same name twice such as john+john+70.
There also must not be two projects in the list containing the same pair of students. So if there’s a project harry+ron+82 in the list, it would be illegal for the list also to contain harry+ron+90 or ron+harry+63.
There is a sample output:
?- legalCourse([one+two+3,four+five+6,one+six+7]).
true.
?- legalCourse([one+two+3,four+four+6,one+six+7]).
false.
?- legalCourse([one+two+3,four+five+6,one+two+7]).
false.
?- legalCourse([one+two+3,two+one+6,one+six+7]).
false.
This is what I tried:
legalCourse([]).
legalCourse(X) :-
diffName(X).
legalCourse([Project|M]):-
diffName(Project),
not(samePair([Project|M])),
legalCourse(M).
diffName(Name1+Name2+_) :-
Name1 \= Name2.
/*can not have duplicated group*/
samePair([Name1+Name2+_|More]) :-
append([[head],tail,More]),
member(Name1,[head]),
member(Name2,[head]).
The function partially worked before I added the samePair predicate.
I think this works, you need to switch the vars and check both are different in check_no_dups/1.
legalCourse(List):-
maplist(triple_double,List,ListDouble),
check_no_dups(ListDouble).
check_no_dups([]).
check_no_dups([H|T]):-
H =X+Y,
maplist(dif(H),T),
H2 =Y+X,
maplist(dif(H2),T),
check_no_dups(T).
triple_double(X+Y+_Z,X+Y):-dif(X,Y).
So I have this knowledge base
family(person(name(tom),surname(fox),date(7,may,1950),job(bbc,15200)),
person(name(ann),surname(fox),date(9,may,1951),job(unemployed)),
children[person(name(pat),surname(fox),date(5,may,1973),job(unemployed)),
person(name(jim),surname(fox),date(5,may,1973),job(unemployed))]).
family(person(name(john),surname(doe),date(7,july,1957),job(carpenter,12300)),
person(name(lucy),surname(doe),date(19,february,1969),job(clerk,13500)),
children[person(name(mary),surname(doe),date(17,january,1990),job(unemployed)),
person(name(mat),surname(doe),date(4,may,1991),job(unemployed)),
person(name(george),surname(doe),date(5,august,1993),job(unemployed))]).
family(person(name(nick),surname(brown),date(14,may,1955),job(trucker,16300)),
person(name(carmen),surname(brown),date(25,april,1957),job(unemployed)),
children[person(name(david),surname(brown),date(15,august,1977),job(unemployed)),
person(name(james),surname(brown),date(7,october,1980),job(unemployed))]).
family(person(name(daniel),surname(sturgess),date(19,november,1956),job(unemployed)),
person(name(susan),surname(sturgess),date(18,october,1957),job(manager,15400)),
children[person(name(mick),surname(sturgess),date(5,december,1982),job(unemployed))]).
And what I'm trying to do is figure out a way to create a predicate wife/1 that will return all the working wives, and a predicate exists/1 that will return all the unemployed parents that are born before 1963.
I'm quite new to Prolog (using the swi environment) so any help is welcome!
Your database is in unusual format, since in Prolog attributes are normally associated to positions. Since you name all attributes, some flexibility is allowed. Assuming a 'working wife' it's the second entry of family/2 having a job \= unemployed at fixed (last) position:
wife(W) :- family(_,W,_), W = person(_,_,_,job(Job)), Job \= unemployed.
to get all:
?- findall(W, wife(W), Wives).
if job/1 attribute can appear in some other argument position, we can generalize the above clause:
wife(W) :- family(_,W,_), W =.. [person|Attrs], memberchk(job(Job), Attrs), Job \= unemployed.
exists/1 can be handled in similar way...
edit
correction to match job attribute: it appears with 1 or 2 arguments: assuming when a person is employed, s(he) will always have a salary, we can simplify matching job/2:
wife(W) :- family(_,W,_), W = person(_,_,_,job(_,_)).
Given this program, why am I forced to define every atom in the predicate, even if they're anonymous. Why is it that undefined variables in a dict predicate aren't thought of as anonymous?
funt2(X) :-
X = point{x:5, y:6}.
evalfunt(point{x:5, y : 6}) :-
write('hello world!').
evalfunt(point{x:_, y : _} ) :-
write('GoodBye world!').
Why can't I just say
evalfunt(point{x:5}) :-
write('GoodBye world!').
^that won't match, by the way.
I may as well just use a structure if I have to define every possible value in the dict to use dicts.
What's the motivation here? Can I do something to make my predicate terse? I'm trying to define a dict with 30 variables and this is a huge roadblock. It's going to increase my program size by a magnitude if I'm forced to define each variables (anonymous or not).
Dict is just a complex data type, like tuple, which has data AND structure. If you have, for example two facts:
fact(point{x:5, y:6}).
fact(point{x:5}).
Then the query
fact(point{x:_}).
will match the second one, but not the first one.
And the query
fact(point{x:_, y:_}).
Will match the first one, but not the second.
Now, if you want to match facts of the form fact(point{x:_, y:_, z:_}) only by one specific field, you can always write a helper rule:
matchByX(X, P) :- fact(P), P=point{x:X, y:_, z:_}.
So having facts:
fact(point{x:5, y:6, z:1}).
fact(point{x:1, y:2, z:3}).
fact(point{x:2, y:65, z:4}).
and quering
matchByX(1, P).
will return:
P = point{x:1, y:2, z:3}
UPDATE:
Moreover, in SWI-Prolog 7 version the field names can be matched as well, so it can be written in much more generic way, even for facts with different structures:
fact(point{x:5, y:6, z:1}).
fact(point{x:1, y:2}).
fact(point{x:2}).
fact(point{x:2, y:2}).
matchByField(F, X, P) :- fact(P), P.F = X.
So query:
?- matchByField(x, 2, P).
P = point{x:2} ;
P = point{x:2, y:2}.
I was able to accomplish what I needed by doing the following
checkiffive(Y) :-
get_dict(x, Y, V), V=5.
You need to use the built in methods for unifying values from a dict.
Described in chapter 5.4 of the SWI prolog reference
http://www.swi-prolog.org/download/devel/doc/SWI-Prolog-7.1.16.pdf