CODEWITHSUNDEEP
prolog
Mr. Adobo
Mr. Adobo

Reputation: 825

What does \+ do in Prolog?

I'm studying this code, and there is a + in the color function which I have no idea what it does. I'm very confused by this and I'm basically stuck on this because I can't understand what it does.

/* prolog  tutorial 2.9 Map coloring redux */
adjacent(X,Y,Map) :-  member([X,Y],Map) ; member([Y,X],Map). 
find_regions([],R,R). 
find_regions([[X,Y]|S], R,A) :- 
 (member(X,R) ->  
  (member(Y,R) -> find_regions(S,R,A) ; find_regions(S,[Y|R],A)) ; 
    (member(Y,R) -> find_regions(S,[X|R],A) ; find_regions(S,[X,Y|R],A) ) ). 

color(Map,Colors,Coloring) :-
    find_regions(Map,[],Regions), 
    color_all(Regions,Colors,Coloring), 
    \+ conflict(Map,Coloring). 
color_all([R|Rs],Colors,[[R,C]|A]) :- 
    member(C,Colors), 
    color_all(Rs,Colors,A). 
color_all([],_,[]). 


conflict(Map,Coloring) :- 
    member([R1,C],Coloring), 
    member([R2,C],Coloring), 
    adjacent(R1,R2,Map). 

map1([[1,2],[1,3],[1,4],[1,5],[2,3],[2,4],[3,4],[4,5]] ).

Upvotes: 2

Views: 7019

Answers (2)

Andi Krusch
Andi Krusch

Reputation: 1383

"In standard Prolog the operator + means negation as failure"

There ist a good Tutorial found here.

Upvotes: 2

Junuxx
Junuxx

Reputation: 14261

It is a negation, see here for a detailed explanation with examples. You can basically just read it as equivalent to 'not', or more accurately, 'not provable'.

Upvotes: 5

Related Questions