Why this if statment only work at first step - prolog

Question

calculateSum(_, _List, _Row, _Col, []).
calculateSum([M|Rest],List,Row,Col,[Y|Tail]):-
Col == Row -> Col1 is Col + 1,calculateSum(List,List,Row1,Col1,Tail);
calcHeu(Rest,L),
sum(L,S),
index(List, Row, Col, V),
Y is V + S,
%Row1 is Row + 1,
Col1 is Col + 1,
calculateSum(List,List,Row1,Col1,Tail).
Why this Col == Row if statement doest work. Is there any other way so that if Row == Col skip that step?
EDIT
By doing some thing like this.
(Col \= Row ->
calcHeu(Rest,L),
sum(L,S),
index(List, Row, Col, V),
Y is V + S,
Col1 is Col + 1,
calculateSum(List,List,Row1,Col1,Tail)
;
Col1 is Col + 1,calculateSum(List,List,Row1,Col1,Tail)
).
it print out [22,,,_...... infinitly

Answer 1

It's a bit hard to tell without knowing what your code is supposed to do and what inputs it gets, but you can definitely break your if-then-else statement into two rules with a cut (which in my opinion is preferable anyways: try to avoid using ";" as much as possible).
Try this (note that I've change the fir occurrence of "List" in the recursive call for "Rest", because I think that's what you want anyways):
calculateSum(_, _List, _Row, _Col, []).
calculateSum([_M|Rest],List,Row,Row,[_Y|Tail]):-
!,
Col1 is Col + 1,
calculateSum(Rest,List,Row1,Col1,Tail).
calculateSum([M|Rest],List,Row,Col,[Y|Tail]):-
calcHeu(Rest,L),
sum(L,S),
index(List, Row, Col, V),
Y is V + S,
Col1 is Col + 1,
calculateSum(Rest,List,Row1,Col1,Tail).