I'm doing a job in Prolog and when trying to make a query it says there are "Singleton variables". For example, a part of the code:
s([Policia_X, Policia_Y, Ladrao_X, Ladrao_Y]) :- pode_andar_horizontal([Policia_X, Policia_Y]).
Returns the error:
Warning: c: /users/leila/desktop/2018.2/ia/ia/trab1.pl: 35: Singleton variables: [Ladrao_X, Ladrao_Y]
What does this mean?
This is a warning to help you with two common errors:
So in your specific case, this warning says that in the trab1.pl file, on the 35 (which is :35 ) line, you may be using variables that were no longer used in this rule or fact. It can also mean a misspelling. In case, to use the variable only once, for example:
teste(A): - t(B, A).
In this case, you can get rid of the warning message by putting (_) in front of the variable singleton , in this case the variable B :
teste(A): - t(_B, A).