Open and Semi-open files

[thevinenator]

i was examining my code for Rook O and SO files and had a thought.

all the definitions i can find define an Open file as one without any pawns on the same file as the rook, for example.

say a white Rook is on F3 and there are no pawns in "front" (moving toward black's side), but the rook has the white F2 pawn behind it. why wouldn't it still be consider open? it is the attacking direction that is important, isn't it?

same goes for SO files.

[hyatt]

Depends. It might make it harder to retreat your rook to defend a pawn from the side. It might make it easier to attack the opponent's king. The idea of an open file is nothing more than a pseudo-mobility term for a rook. No pawns = more squares the rook can move to or control. As far as whether a "lifted rook" (which is what you are describing) is good or not depends on the position. In the majority of positions, being on the normally open file is the best place. But if you want to deal with special cases, then you can add a second term for a rook in front of a friendly pawn and attacking the enemy king even if he also has a pawn in front of your rook.

So a general rule vs multiple more specific rules. The latter have a computational cost that the first does not, but the latter provide more accuracy, which the first does not. It's a trade-off.