Question

I need to develop a predicate in Prolog able to compare a list against fact. In other words, if the names of the products residing in the list are all in the database(fact) as well, then it gotta say “yes”, otherwise “no”.
The predicate obviously receives a list of the products names.
At the moment, I’ve got this piece of code.

domains
    state =  reduced ; normal
    element = string
    list = element*
database
    producte (string, integer, state)
predicates
    nondeterm check(list)
clauses 
   % ---> producte( description , price , state )
    producte("Enciam",2,normal). 
    producte("Llet",1,reduced). 
    producte("Formatge",5,normal). 
    %unique case
    check([Name]):-
        producte([Name],_,_).
    %general case
    check([D|T]):-
        producte(D,_,_),
        check(T).
Goal
    check(["Enciam","Llet","Formatge"]).

Answer 1

Your base case for check looks for the product’s name as a list instead of as a string.