I have a simple prolog program:
write_manual:-
write('------------------------------'),
write('USAGE MANUAL'),
write('find_course. - List all the available courses'),
write('------------------------------').
% execute this and output this right away when I open the program in the console
Does anyone know to achieve this? I'd like to print a simple help manual before the program starts. Currently, the swi prolog console (on windows 10) shows the ?- prompt and requires me to
manually call the predicate. I'm using SWI-Prolog (threaded, 64 bits, version 8.0.0).
This is a comment posted in a question because it doesn't format correctly in a comment.
Running on Windows 10 with SWI-Prolog (threaded, 64 bits, version 8.1.21)
:- initialization main.
main :-
write_manual.
write_manual :-
format('------------------------------~n',[]),
format('USAGE MANUAL~n',[]),
format('find_course. - List all the available courses~n',[]),
format('------------------------------~n',[]).
Start SWI-Prolog
?- consult("C:/Prolog/SO_question_160.pl").
------------------------------
USAGE MANUAL
find_course. - List all the available courses
------------------------------
true.
?-
Note: This was not setup to start from a Windows command line script because the title of the question reads I consult a file.
Related
If I have a prolog file defining the rules, and open it in a prolog terminal in windows, it loads the facts. However, then it shows the ?- prompt for me to manually type something. How can I add code to the file, so that it will actually evaluate those specific statements as if I typed them in?
something like this
dog.pl
dog(john).
dog(ben).
% execute this and output this right away when I open it in the console
dog(X).
Does anyone know how to do this?
Thanks
There is an ISO directive on this purpose (and more): initialization
If you have a file, say dog.pl in a folder, with this content
dog(john).
dog(ben).
:- initialization forall(dog(X), writeln(X)).
when you consult the file you get
?- [dog].
john
ben
true.
Note that just asserting dog(X). doesn't call dog(X) as a query, but rather attempts to assert is as a fact or rule, which it will do and warn about a singleton variable.
Here's a way to cause the execution the way you're describing (this works for SWI Prolog, but not GNU Prolog):
foo.pl contents:
dog(john).
dog(ben).
% execute this and output this right away when I open it in the console
% This will write each successful query for dog(X)
:- forall(dog(X), (write(X), nl)).
What this does is write out the result of the dog(X) query, and then force a backtrack, via the false call, back to dog(X) which will find the next solution. This continues until there are no more dog(X) solutions which ultimately fails. The ; true ensures that true is called when dog(X) finally fails so that the entire expression succeeds after writing out all of the successful queries to dog(X).
?- [foo].
john
ben
true.
You could also encapsulate it in a predicate:
start_up :-
forall(dog(X), (write(X), nl)).
% execute this and output this right away when I open it in the console
:- start_up.
If you want to run the query and then exit, you can remove the :- start_up. from the file and run it from the command line:
$ swipl -l foo.pl -t start_up
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 7.2.3)
Copyright (c) 1990-2015 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.
For help, use ?- help(Topic). or ?- apropos(Word).
john
ben
% halt
$
dog.pl:
dog(john).
dog(ben).
run :- dog(X), write(X).
% OR:
% :- dog(X), write(X).
% To print only the first option automatically after consulting.
Then:
$ swipl
1 ?- [dog].
% dog compiled 0.00 sec, 4 clauses
true.
2 ?- run.
john
true ; # ';' is pressed by the user
ben
true.
3 ?-
Typing "prolog" in terminal gets:
GNU Prolog 1.3.0
By Daniel Diaz
Copyright (C) 1999-2007 Daniel Diaz
| ?-
Typing:
| ?- member(2, [1,2,3]).
Gets:
true ?
Then pressing enter gets:
yes
Typing:
| ?- member(4, [1,2,3]).
gets:
no
When i write a file; test.pl consisting of this:
:- member(4, [1,2,3]), nl, halt.
And then write in the terminal:
| ?- [test2].
I get:
compiling /path/test.pl for byte code...
/path/test.pl:1: warning: unknown directive (',')/2 - maybe use initialization/1 - directive ignored
/path/test.pl compiled, 1 lines read - 139 bytes written, 11 ms
yes
Shouldnt the answer here be no? What am i doing wrong. Also, how would you do this in prolog:
if (testInPrologTerminal(member(4, [1,2,3])) { do this; }
I.e, i want to send queries to the prolog top level, and get an answer
When you type the query member(2, [1,2,3]), GNU Prolog prompts you for a possible additional solution (hence the true ? prompt) as only by backtracking (and looking to the last element in the list, 3) it could check for it. When you press enter, you're telling the top-level interpreter that you are satisfied with the current solution (the element 2 in the list second position). The second query, member(4, [1,2,3]), have no solutions so you get a no.
To execute a query when a file is loaded, the standard and portable way of doing it, is to use the standard initialization/1 directive. In this case, you would write:
:- initialization((member(4, [1,2,3]), nl, halt)).
Note the ()'s surrounding the query, otherwise you may get a warning about an unknown initialization/3 standard, built-in, control construct. If you have more complex queries to be executed when a file is loaded, then define a predicate that makes the queries a call this predicate from the initialization/1 directive. For example:
main :-
( member(4, [1,2,3]) ->
write('Query succeeded!'), nl
; write('Query failed!'), nl
).
:- initialization(main).
Writing arbitrary queries as directives in a source file is legacy practice and thus accepted by several Prolog implementations but using the initialization/1 directive is the more clean, standard, and portable alternative.
I have successfully connected PHP with Prolog and managed to query the desired knowledge base that resides in knowledge_base.pl file and managed to echo the results via php exec function.
I encountered a problem in echoing the true/false value that Prolog returns after each query execution (see previous question) so I came up with a solution that I have trouble implementing.
Let's assume I have a simple knowledge_base.pl file with these facts and rules:
girl(erin).
boy(john).
likes(erin, reading).
likes(john, reading).
hangs_out_with(erin, X) :-
likes(X, reading),
boy(X),
writeln('Someone s got a new friend!!').
Lets say that I want to see if erin is a girl and if so, write that it is true, or else write that it is false. I added this to my knowledge_base.pl file:
girl(erin) :-
girl(erin)
-> write('it is true')
; write('it is not true').
When I enter the query: ?- girl(erin). I get an out of local stack error. I searched the Web and found out that this is due to infinite recursion.
Can someone give me a hint in how to write
girl(X) :-
( girl(X)
-> write('it is true')
; write('it is not true')).
in Prolog? Thanks in advance.
As a new user I'm not allowed to post pictures.
SWI-Prolog's output:
1 ?-hangs_out_with(erin,kosta).
false.
2 ?-hangs_out_with(erin,john).
Someone s got a new friend!!
true.
Command prompt's output:
C:\(directory)>swipl -q -f knowledge_database.pl -g hangs_out_with(erin,kosta),halt.
1 ?-halt. (the halt is inputted by me.)
C:\(directory)>swipl -q -f knowledge_database.pl -g hangs_out_with(erin,john),halt.
Someone s got a new friend!!
The first query fails and the second succeds. As you can see, prolog after the query executions outputs true/false but when i execute the same query in command prompt the true/false values do not get echoed!!
I think you should ask
is_girl(X) :-
girl(X) -> write('t is true') ; write('it is not true').
EDIT
Do you mean this kind of thing ?
is_type(Type, X) :-
call(Type, X) -> writeln(yes); writeln(no).
so you "connect PHP to Prolog" by executing a Prolog query in command shell and capturing and analyzing its output. http://www.swi-prolog.org/man/quickstart.html says
"2.1.1.1 Starting SWI-Prolog on Unix
By default, SWI-Prolog is installed as 'swipl'. The command-line arguments of SWI-Prolog itself and its utility programs are documented using standard Unix man pages."
So do consult a man page about "-q" switch. Is it the "-q" for quiet perhaps? What does "-f" mean (ok, that's probably "file")? But the solution is the same - just use a different name for the new predicate.
Notice that in your first attempt,
C:>swipl -q -f knowledge_database.pl -g hangs_out_with(erin,kosta),halt.
1 ?-halt. (the halt is inputted by me.)
halt isn't executed, precisely because hangs_out_with(erin,kosta) has failed. A comma signifies conjunction (an "and").
All you need to do is create a new predicate that reports whether the goal is true or false, and succeeds always:
report_hangs_out_with(A,B):-
hangs_out_with(A,B)- > writeln(['YES',A,B]) ; writeln('NO').
and use it instead:
C:>swipl -q -f knowledge_database.pl -g report_hangs_out_with(erin,kosta),halt.
Also, Prolog echoing "true" or "false" is part of its interactive session. But you terminate it with halt!
edit: you posted:
1 ?-hangs_out_with(erin,kosta).
false.
So, when you run that query in interactive Prolog shell, it reports the failure. halt/0 exits the Prolog shell. When you run it with a goal specified through command line switch, apparently it does not report the success of failure. That's the fact of nature as far as we users are concerned (a.o.t. the compiler writers). It is easily addressable with what I've shown you. And you yourself say that it works, too. For each predicate that can fail or succeed, define another, reporting predicate, just as I've shown you.
Here's a sample transcript (in Windows, but that's irrelevant). That should clear up your doubts:
C:\Program Files\pl\bin>plcon -q -g (writeln('****'),halt).
**** // didn't say Yes, right??
C:\Program Files\pl\bin>plcon -q
1 ?- writeln('****'),halt.
**** // didn't say Yes here either
C:\Program Files\pl\bin>plcon -q
1 ?- writeln('****').
****
Yes // does say Yes as part of interaction
2 ?- halt.
C:\Program Files\pl\bin>
So that's the way it is. Deal with it. :) Or write Jan and ask him to change it. :)
girl(erin) :-
girl(erin)
-> write('it is true')
; write('it is not true').
This is wrong for two reasons. Prolog tries to resolve the body taking the left-most literal.
So it basically goes in a loop "is erin girl? yes, if erin is girl. Is erin girl?..."
The second reason is you are mixing two different things. Try to keep your knowledge representation part separated from the way you use it.
In Prolog you just say:
girl(erin)
And then query
?- girl(erin)
Prolog will just say "yes". If you want to print it, probably the easiest way is adding a predicate.
check_and_print(X) :- X, write(X), write(" is true").
Probably you need a call(X) instead of X, depending on the implementation you are using.
I'm not sure about the command prompt out, I suspect the outcome is returned in a different way.
I'm brand new to Prolog. I am simply trying to get some output from Prolog on Windows Vista.
I have downloaded and installed Prolog 5.1; I chose the .pro file extension when installing (not to confuse with Perl files).
I created a file called test.pro.
Inside this file I put the following:
inside(tom).
?-inside(tom).
I double clicked the file and a command line interface popped up. On this interface (after a bunch of generic Prolog version/copyright info) the only output is:
1 ?-
OK, for starters, I did not expect it to ask a question; I expected it to answer a question (something along the line of 'yes').
Anyway, I tried to respond to the query with the following:
In the command line I re-inserted 'inside(tom).', so the whole line looks like:
1 ?- inside(tom).
I pressed Enter and got an error message:
ERROR: toplevel: Undefined procedure: inside/1 (DWIM could not correct goal)
Prolog doesn't answer questions if you haven't told it facts. (Except for some built-in facts such as member(1, [1,2,3]).)
You can tell it who is inside by (comment follow a %):
1 ?- [user]. % get facts and rules from user input
|: inside(mary). % Mary and John are explicitly inside
|: inside(john).
|: inside(X) :- location(X, house). % rule: anyone in the house is inside
|: inside(X) :- location(X, office). % (variables start with a capital letter)
|:
|: location(tom, house).
|: location(bernard, house).
|: location(anne, office).
|: % type Ctrl+D
% user://1 compiled 0.00 sec, 1,220 bytes
true.
2 ?- inside(tom). % Prolog deduces that Tom is inside
true .
If you want to learn Prolog, Learn Prolog Now is a good, free tutorial.
You need to compile this first (also called "consult" in prolog). If I knew which version of prolog you have I could find out the exact key entry for this command (Ctrl-L may work). By the way, welcome to the wonderful world of prolog- I love it :) As soon as you're over this hurdle, it gets a lot better. :)
Quick and dirty. What was missing was 'compiling' the file, known as consult
and the syntax is as follows, all characters in the line are relevant.
?- [filename].
then you can ask questions and do other things with what the database.(the source code in prolog)
http://www.swi-prolog.org/pldoc/man?section=quickstart
I'm new to SWI-Prolog and am trying some tutorials. Every file I try to load through the command line, however, gets 2 error messages - one at the start (Operator expected) and one at the end (Unexpected end of file). Files are saved in the same directory as the one I'm working in.
For example, I have this file saved as kb2.pl
listensToMusic(mia).
happy(yolanda).
playsAirGuitar(mia) :- listensToMusic(mia).
playsAirGuitar(yolanda) :- listensToMusic(yolanda).
listensToMusic(yolanda):- happy(yolanda).
From the start of opening Prolog (through /opt/local/bin/swipl), my command line looks like this:
% library(swi_hooks) compiled into pce_swi_hooks 0.00 sec, 3,928 bytes
Welcome to SWI-Prolog (Multi-threaded, 64 bits, Version 5.10.2)
Copyright (c) 1990-2010 University of Amsterdam, VU Amsterdam
SWI-Prolog comes with ABSOLUTELY NO WARRANTY. This is free software,
and you are welcome to redistribute it under certain conditions.
Please visit http://www.swi-prolog.org for details.
help, use ?- help(Topic). or ?- apropos(Word).
?- [kb2].
ERROR: /Users/name/Desktop/kb2.pl:1:0: Syntax error: Operator expected
ERROR: /Users/name/Desktop/kb2.pl:10:52: Syntax error: Unexpected end of file
% kb2 compiled 0.00 sec, 2,584 bytes
true.
?-
When I ask for the listing of the compiled file, I get:
\happy(yolanda).
\playsAirGuitar(mia) :- listensToMusic(mia).
\playsAirGuitar(yolanda) :- listensToMusic(yolanda).
true.
So it's cutting out the first and last lines of the file.
I've searched for these error messages online and found a lot of useful hints about formatting for Prolog, but none that address this situation. Is there some sort of special character or formatting that should be used for the start and end of a file for Prolog?
Which operating system are you on? Are you sure the file is ASCII (and not UTF-16)? Does it have the native line ending for your platform? Can you post the whole file (raw) so people can check it?
Many Prolog systems, such as SWI-Prolog, Jekejeke Prolog, allow to detect a BOM as the first character of a text file. The BOM is some white space, that indicates the encoding of the text file:
254 255 UTF-16BE
255 254 UTF-16LE
239 187 191 UTF-8
So there is no need to restrict yourself to ASCII. Many text editors will place the BOM for you. And SWI-Prolog, Jekejeke Prolog, by default probe the BOM.