列表中的 Prolog-Sum 正数

Question

I have the following Prolog fact to sum the positive numbers from a list but it´s not working. What am I doing wrong?

somarPositivos([],0).
somarPositivos([H|T],Soma):-H>0,somarPositivos(T,Soma1),Soma is Soma1+H.
somarPositivos([H|T],Soma):-H=<0 ,somarPositivos(T,Soma1).

Answer 1

You have a typo in the third clause. It should be:

somarPositivos([H|T],Soma):-H=<0 ,somarPositivos(T,Soma).

Most Prolog compilers would print a warning that the variables Soma and Soma1 are singleton variables in that clause.

Some notes on programming style following Prolog coding guidelines. Indent your code. Use spaces around operators. Use underscores instead of camelCase for predicate names for readbility. Thus, preferably write:

somar_positivos([],0).
somar_positivos([H|T],Soma) :-
    H > 0,
    somar_positivos(T,Soma1),
    Soma is Soma1+H.
somar_positivos([H|T],Soma) :-
    H =< 0,
    somar_positivos(T,Soma).

As an improvement to this initial version of the predicate, can you rewrite it to make it tail-recursive using an accumulator?