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  • prolog to solve grammar involving braces

    - by Abhilash Muthuraj
    I'm trying to solve DCG grammar in prolog and succeeded upto a point, i'm stuck in evaluating the expressions involving braces like these. expr( T, [’(’, 5, +, 4, ’)’, *, 7], []), expr(Z) --> num(Z). expr(Z) --> num(X), [+], expr(Y), {Z is X+Y}. expr(Z) --> num(X), [-], expr(Y), {Z is X-Y}. expr(Z) --> num(X), [*], expr(Y), {Z is X*Y}. num(D) --> [D], {number(D)}. eval(L, V, []) :- expr(V, L, []).

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  • SWI-Prolog Semantic Web Library and Python Interface

    - by John Peter Thompson Garcés
    I want to write a Python web application that queries RDF triples using Prolog. I found pyswip for interfacing Python with SWI-Prolog, and I am currently looking into SWI-Prolog's RDF capabilities. I am wondering if anyone has tried this before--and if anyone has: what did your setup look like? How do you get pyswip to work with the SWI-Prolog semantic web library? Or is there another Python-Prolog interface that makes this easier?

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  • Prolog - ASSERT and RETRACT

    - by KP65
    I was wondering, I am aware you can use assert to add facts or rules or whatever if you have declared the predicate to be -:dynamic, but this only allows the changes that are made to be kept in that session only, e.g. if you close the prolog window then the database changes are lost. So I was wondering, is there any way of making it so that the assert and retract predicates can make permanent changes to the prolog .pl file? Thanks

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  • print customized result in prolog

    - by Allan Jiang
    I am working on a simple prolog program. Here is my problem. Say I already have a fact fruit(apple). I want the program take a input like this ?- input([what,is,apple]). and output apple is a fruit and for input like ?-input([is,apple,a,fruit]) instead of default print true or false, I want the program print some better phrase like yes and no Can someone help me with this? My code part is below: input(Text) :- phrase(sentence(S), Text), perform(S). %... sentence(query(Q)) --> query(Q). query(Query) --> ['is', Thing, 'a', Category], { Query =.. [Category, Thing]}. % here it will print true/false, is there a way in prolog to have it print yes/no, %like in other language: if(q){write("yes")}else{write("no")} perform(query(Q)) :- Q.

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  • loading files in prolog

    - by cubearth
    hey guys, am a bit of a newbie in Prolog. And am going thru this tutorial on line and it is telling me i can load other prolog files by typing: [filename]. but ever time I try this am getting ERROR: load_files/2: Arguments are not sufficiently instantiated. What am i doing wrong? P.S. the file is in the same directory as the one am working in. and here is a copy of the entire query and error. 12 ?- [KB5]. ERROR: load_files/2: Arguments are not sufficiently instantiated

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  • Scheduling of tasks to a single resource using Prolog

    - by Reed Debaets
    I searched through here as best I could and though I found some relevant questions, I don't think they covered the question at hand: Assume a single resource and a known list of requests to schedule a task. Each request includes a start_after, start_by, expected_duration, and action. The goal is to schedule the tasks for execution as soon as possible while keeping each task scheduled between start_after and start_by. I coded up a simple prolog example that I "thought" should work but I've been unfortunately getting errors during run time: "=/2: Arguments are not sufficiently instantiated". Any help or advice would be greatly appreciated startAfter(1,0). startAfter(2,0). startAfter(3,0). startBy(1,100). startBy(2,500). startBy(3,300). duration(1,199). duration(2,199). duration(3,199). action(1,'noop1'). action(2,'noop2'). action(3,'noop3'). can_run(R,T) :- startAfter(R,TA),startBy(R,TB),T>=TA,T=<TB. conflicts(T,R1,T1) :- duration(R1,D1),T=<D1+T1,T>T1. schedule(R1,T1,R2,T2,R3,T3) :- can_run(R1,T1),\+conflicts(T1,R2,T2),\+conflicts(T1,R3,T3), can_run(R2,T2),\+conflicts(T2,R1,T1),\+conflicts(T2,R3,T3), can_run(R3,T3),\+conflicts(T3,R1,T1),\+conflicts(T3,R2,T2). % when traced I *should* see T1=0, T2=400, T3=200 Edit: conflicts goal wasn't quite right: needed extra TT1 clause. Edit: Apparently my schedule goal works if I supply valid Request,Time pairs ... but I'm stucking trying to force prolog to find valid values for T1..3 when given R1..3?

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  • Do most programmers cut & paste code?

    - by John MacIntyre
    I learned very early on that cutting & pasting somebody else's code takes longer in the long run that writing it yourself. In my opinion unless you really understand it, cut & paste code will probably have issues which will be a nightmare to resolve. Don't get me wrong, I mean finding other peoples code and learning from it is essential, but we don't just paste it into our app. We rewrite the concepts into our app. But I'm constantly hearing about people who cut & paste, and they talk about it like it's common practice. I also see comments by others which indicate it's common practice. So, do most programmers cut & paste code?

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  • Prolog instantiation error?

    - by KP65
    Hello guys, I'm stuck with some sort of error which i don't really understand in prolog. I get this error when calling a rule(which seems to work sometimes?) : error(instantiation_error,Var0) Can anyone explain to me what this means? Thanks

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  • Prolog - Finding the current directory, relative directory for 'tell' predicate

    - by Bharat
    I'm having trouble trying to figure out how to get prolog to spit out a text file where I want it to. I'm currently doing a bunch of operations and then using tell('output.txt') to record the output. Now the problem is that when I do this, it creates this file in the SWI \bin\ folder. I was wondering if there's a way to make it create this file in the directory containing the actual .pl file. So even if the file was moved (and it will be), the text file gets created right where the source file is. Long story short, is there a way to get the location of the source file once the source file has been consulted? Many Thanks!

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  • Inverse Factorial Function (Prolog)

    - by user2796815
    I have to write a Prolog program to computer the inverse of factorial function without using division. I was also given the note: "the inverse of a function is not necessarily a function". I have this is a normal factorial predicate.. fact(0,1). fact(N,F) :- N0, N1 is N-1, fact(N1,F1), F is N * F1. I've read on some other posts that you should be able to just switch around the arguments, but that doesn't seem to be the case with this version. Could anyone help me out with figuring out why?

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  • Counting Sublist Elements in Prolog

    - by idea_
    How can I count nested list elements in prolog? I have the following predicates defined, which will count a nested list as one element: length([ ], 0). length([H|T],N) :- length(T,M), N is M+1. Usage: ?- length([a,b,c],Out). Out = 3 This works, but I would like to count nested elements as well i.e. length([a,b,[c,d,e],f],Output). ?- length([a,b,[c,d,e],f],Output). Output = 6

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  • NP-complete problem in Prolog

    - by Ashley
    I saw this ECLiPSe solution to the problem mentioned in this XKCD comic. I tried to convert this to pure Prolog. go:- Total = 1505, Prices = [215, 275, 335, 355, 420, 580], length(Prices, N), length(Amounts, N), totalCost(Prices, Amounts, 0, Total), writeln(Total). totalCost([], [], TotalSoFar, TotalSoFar). totalCost([P|Prices], [A|Amounts], TotalSoFar, EndTotal):- between(0, 10, A), Cost is P*A, TotalSoFar1 is TotalSoFar + Cost, totalCost(Prices, Amounts, TotalSoFar1, EndTotal). I don't think that this is the best / most declarative solution that one can come up with. Does anyone have any suggestions for improvement? Thanks in advance!

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  • Prolog: permutations check and multiple answers

    - by Adrian
    Continuing to learn prolog, I'm trying to write a permutation(L1, L2) predicate. It should return true, only if L1 can be made up of all elements in L2. My code so far is the following: permutation([], []). permutation([H|T], L2) :- remove(L2, H, R), permutation(T, R). Assuming that the predicate remove(L1, X, R) functions correctly, and it removes X from L1, I do not get correct results: ?- permutation([1],[1]). true ; false. ?- permutation([1, 2],[1]). true ; false. ?- permutation([1, 2],[1, 2]). true ; false. ?- permutation([1],[1, 2]). false. What am I missing. Subquestion: What happens when the remove predicate returns two answers? My implementation returns the new, correct list, and then after pressing ; it returns the original list. Which answer does permutation predicate use? ?- remove([1,2,3], 3, R). R = [1, 2] ; R = [1, 2, 3].

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  • Prolog: How to make three lists the same lenght (by adding leading zeros)

    - by sixtyfootersdude
    I am writing a prolog program to solve a problem. The problem takes three lists as input: solve( [L|Lr] , [R|Rr] , [S|Sr] ) :- Unfortunately the lists all need to be equal length for the program to work. So these work: ?- solve( [A, B, C, D] , [1, 3, 5, 6], [E, F, G, H]). ?- solve( [1] , [2], [3]). But these do not: ?- solve( [A, B, C, D], [1], [B, I, T] ). ?- solve( [A], [1, 2], [4, 5]). What I would like to do is write a predicate(?) to pad the smaller lists with leading zeros. So: solve( [A, B, C, D], [1], [B, I, T] ) would become: solve( [A, B, C, D], [0, 0, 0, 1], [0, B, I, T] ) Any points on how to accomplish this would be awesome. I am from a functional background so I am struggling. Is there a way tell the length of a list? I think I could do that recursively, but it seems like a pain. Thanks

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  • Prolog check if

    - by NickLee
    I'm creating a text adventure game on SWI-Prolog and I want to include (some kind of) dialogs. What I have so far is: dialog1(1):- nl,write('blah blah'),nl write('a: this is answer a'),nl, write('b: this is answer b'),nl. a:- write('respond to answer a'),nl. b:- write('respond to answer b'),nl. That's pretty much the first dialog. Now I want to create a second dialog similar to the first one. dialog1(2):- nl,write('blah blah'),nl, write('a: this is answer a'),nl, write('b: this is answer b'),nl. a:- write('respond to answer a'),nl. b:- write('respond to answer b'),nl. How can I check if the dialog is the first or the second one? I want to do that because when the user types a., I need the right answer a to be shown. I thought I could use something like a(1):- write('respond to answer a'),nl. b(1):- write('respond to answer b'),nl. /* and on the second dialog*/ a(2):- write('respond to answer a'),nl. b(2):- write('respond to answer b'),nl. But still, if the user is on dialog 2 and he types a(1),the first answer will appear.

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  • flushing database cache in SWI-Prolog

    - by JPro
    We are using swi-prolog to run our testcases. Whenever the test starts, I am opening the connection to MYSQL database and storing the Name of the Test hat is being done and then closing the DB. These tests run for about 2 days continuously. After the tests are done, the results basically gets stored in folder in the server. There is a predicate in another prolog file that is called to update the results to the MYSQL database. The code is simple, I use odbc library and just call odbc_* predicates to connect and update the mysql by issuing direct queries. The actual problem is : If I try to call the Predicate from the same Prolog window, where the test just got completed, I get an error as updating to the DB server. Although I do not get any error in the connection. If I close the session of that prolog with halt and closing all the open prolog windows , then open an other complete new instance of Prolog and run the predicate the update goes well. I have a feeling that there is some connection reference to the MySQL DB in Prolog database. Is there any way to clear the database in prolog so that I can run the same predicate without closing any existing prolog windows? Any ideas appreciated. Thanks.

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  • SWI-Prolog tokenize_atom/2 replacement?

    - by Shark
    What I need to do is to break atom to tokens. E. g.: tokenize_string('Hello, World!', L). would unify L=['Hello',',','World','!']. Exactly as tokenize_atom/2 do. But when I try to use tokenize_atom/2 with non-latin letters it fails. Is there any universal replacement or how I can write one? Thanks in advance.

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  • Generalizing Fibonacci sequeue with SICStus Prolog

    - by Christophe Herreman
    I'm trying to find a solution for a query on a generalized Fibonacci sequence (GFS). The query is: are there any GFS that have 885 as their 12th number? The initial 2 numbers may be restricted between 1 and 10. I already found the solution to find the Nth number in a sequence that starts at (1, 1) in which I explicitly define the initial numbers. Here is what I have for this: fib(1, 1). fib(2, 1). fib(N, X) :- N #> 1, Nmin1 #= N - 1, Nmin2 #= N - 2, fib(Nmin1, Xmin1), fib(Nmin2, Xmin2), X #= Xmin1 + Xmin2. For the query mentioned I thought the following would do the trick, in which I reuse the fib method without defining the initial numbers explicitly since this now needs to be done dynamically: fib2 :- X1 in 1..10, X2 in 1..10, fib(1, X1), fib(2, X2), fib(12, 885). ... but this does not seem to work. Is it not possible this way to define the initial numbers, or am I doing something terribly wrong? I'm not asking for the solution, but any advice that could help me solve this would be greatly appreciated.

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  • writing 'remove' function in prolog

    - by Adrian
    I am desperately trying to create a remove function, that will simply remove all items that equal to X from a list. After many changes, this is my code so far: remove([], X, L1). /* when the source list is empty, stop*/ remove([X|T], X, L1) :- remove(T, X, L1). /* when first element in the list equals X, don't append it to L1 */ remove([H|T], X, L1) :- remove(T, X, [H|L1]). /*when first element in the list doesn't equal X, append it to L1 */ when running on remove([1,2,3,4,5], 3, R). it returns two trues and nothing else. Anyone has any idea what I'm doing wrong?

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  • Prolog: Not executing code as expected.

    - by Louis
    Basically I am attempting to have an AI agent navigate a world based on given percepts. My issue is handling how the agent moves. Basically, I have created find_action/4 such that we pass in the percepts, action, current cell, and the direction the agent is facing. As it stands the entire code looks like: http://wesnoth.pastebin.com/kdNvzZ6Y My issue is mainly with lines 102 to 106. Basically, in it's current form the code does not work and the find_action is skipped even when the agent is in fact facing right (I have verified this). This broken code is as follows: % If we are headed right, take a left turn find_action([_, _, _, _, _], Action, _, right) :- retractall(facing(_)), assert(facing(up)), Action = turnleft . However, after some experimentation I have concluded that the following works: % If we are headed right, take a left turn find_action([_, _, _, _, _], Action, _, _) :- facing(right), retractall(facing(_)), assert(facing(up)), Action = turnleft . I am not entire sure why this is. I've attempted to create several identical find_action's as well, each checking a different direction using the facing(_) format, however swipl does not like this and throws an error. Any help would be greatly appreciated.

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  • substitute in a nested list (prolog)

    - by linda
    /* substitute(X,Y,Xs,Ys) is true if the list Ys is the result of substituting Y for all occurrences of X in the list Xs. This is what I have so far: subs(_,_,[],[]). subs(X,Y,[X|L1],[Y|L2]):- subs(X,Y,L1,L2). subs(X,Y,[H|L1],[H|L2]):- X\=H, not(H=[_|_]), subs(X,Y,L1,L2). subs(X,Y,[H|_],[L2]):- X\=H, H=[_|_], subs(X,Y,H,L2). My code works except it omits the elements following the nested list. For example: ?- subs(a,b,[a,[a,c],a],Z). Z = [b, [b, c]] . What should I add to this program?

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  • Generalizing Fibonacci sequence with SICStus Prolog

    - by Christophe Herreman
    I'm trying to find a solution for a query on a generalized Fibonacci sequence (GFS). The query is: are there any GFS that have 885 as their 12th number? The initial 2 numbers may be restricted between 1 and 10. I already found the solution to find the Nth number in a sequence that starts at (1, 1) in which I explicitly define the initial numbers. Here is what I have for this: fib(1, 1). fib(2, 1). fib(N, X) :- N #> 1, Nmin1 #= N - 1, Nmin2 #= N - 2, fib(Nmin1, Xmin1), fib(Nmin2, Xmin2), X #= Xmin1 + Xmin2. For the query mentioned I thought the following would do the trick, in which I reuse the fib method without defining the initial numbers explicitly since this now needs to be done dynamically: fib2 :- X1 in 1..10, X2 in 1..10, fib(1, X1), fib(2, X2), fib(12, 885). ... but this does not seem to work. Is it not possible this way to define the initial numbers, or am I doing something terribly wrong? I'm not asking for the solution, but any advice that could help me solve this would be greatly appreciated.

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  • Prolog - generate correct bracketing

    - by Henrik Bak
    I'd like to get some help in the following exam problem, i have no idea how to do this: Input: a list of numbers, eg.: [1,2,3,4] Output: every possible correct bracketing. Eg.: (in case of input [1,2,3,4]): ((1 2) (3 4)) ((1 (2 3)) 4) (1 ((2 3) 4)) (1 (2 (3 4))) (((1 2) 3) 4) Bracketing here is like a method with two arguments, for example multiplication - then the output is the possible multiplication orders. Please help, i'm stuck with this one. Any help is appreciated, thanks!

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