Prolog : counting values in a list

Question

I have facts with numeric attributes (letters with assigned numeric values).

point(a, 1).

point(b, 3).

point(c, 3).

%etc for the rest of the alphabet

I need to write a programme in Prolog that would count these attributes in a list. Instead, now I only managed to count elements in the list, not their attributes. Could you give me any advice? That would help me a lot !

count_points([ ], 0).

count_points([H|T], Count) :-
    count_points(T, Number),
    Count is Number + 1.

The answer should reproduce following example input/output:

?- count_points([h,e,l,p], Score).

    Score = 14.

I wrote 14, but it depends of the assigned number to the letter.

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Uriel Uriel · Accepted Answer · 2017-01-31T19:06:28

I would go with (see here online):

point(u, 1).
point(r, 2).
point(i, 3).
point(e, 4).
point(l, 5).

count_points([], 0).
count_points([H|T], Count) :- count_points(T, N), point(H, P), Count is N + P.

% count_points([u, r, i, e, l], X).
% X = 15

Prolog : counting values in a list

1 Answers