Prolog Cut Not Working
- by user2295607
Im having a problem with Prolog since cut is not doing what (i believe) its supposed to do:
% line-column handlers
checkVallEle(_, _, 6, _):- write('FAIL'), !, fail.
checkVallEle(TABULEIRO, VALUE, LINE, COLUMN):- COLUMN>5, NL is LINE+1, checkVallEle(TABULEIRO, VALUE, NL, 0).
% if this fails, it goes to the next
checkVallEle(TABULEIRO, VALUE, LINE, COLUMN):-
(checkHorizontal(TABULEIRO, VALUE, LINE, COLUMN, 0), write('HORIZONTAL ');
checkVertical(TABULEIRO, VALUE, LINE, COLUMN, 0), write('VERTICAL');
checkDiagonalRight(TABULEIRO, VALUE, LINE, COLUMN, 0), write('DIAGONALRIGHT');
checkDiagonalLeft(TABULEIRO, VALUE, LINE, COLUMN, 0), write('DIAGONALLEFT')),
write('WIN').
% goes to the next if above fails
checkVallEle(TABULEIRO, VALUE, LINE, COLUMN):-
NC is COLUMN+1,
checkVallEle(TABULEIRO, VALUE, LINE, NC).
What I wish to do is that if the code ever reaches the first statement, that is, if the line is ever 6, it fails (since it went out of range), without checking for more possibilities. But what happens is, when it reaches the first statement, it keeps going to the below statements and ignores the cut symbol, and I dont see why. I just want the statement to fail when it reaches the first line.
I also made an experience...
run(6):-write('done'), !, fail.
run(X):-X1 is X+1, run(X1).
And this is what i get from tracing:
| ?- run(0).
1 1 Call: run(0) ?
2 2 Call: _1079 is 0+1 ?
2 2 Exit: 1 is 0+1 ?
3 2 Call: run(1) ?
4 3 Call: _3009 is 1+1 ?
4 3 Exit: 2 is 1+1 ?
5 3 Call: run(2) ?
6 4 Call: _4939 is 2+1 ?
6 4 Exit: 3 is 2+1 ?
7 4 Call: run(3) ?
8 5 Call: _6869 is 3+1 ?
8 5 Exit: 4 is 3+1 ?
9 5 Call: run(4) ?
10 6 Call: _8799 is 4+1 ?
10 6 Exit: 5 is 4+1 ?
11 6 Call: run(5) ?
12 7 Call: _10729 is 5+1 ?
12 7 Exit: 6 is 5+1 ?
13 7 Call: run(6) ?
14 8 Call: write(done) ?
done
14 8 Exit: write(done) ?
13 7 Fail: run(6) ?
11 6 Fail: run(5) ?
9 5 Fail: run(4) ?
7 4 Fail: run(3) ?
5 3 Fail: run(2) ?
3 2 Fail: run(1) ?
1 1 Fail: run(0) ?
no
What are all those Fails after the write? is it still backtracing to previous answers? Is this behaviour the reason why cut is failing in my first code? Please enlighten me.
