Searching forward and backward from a position
CQL offers several filters that match a position depending on what happened previously or subsequently in the game. Each of these filters' names' begins with the stringnext or previous, depending on whether the filter is looking forward or backward in the game:
| filter name | example | description |
|---|---|---|
| next | next (check check mate)next (check+ mate) |
Filters in the argument list match subsequent positions, starting with current position |
| next2 | next2 (check check mate)next2 (check+ mate) |
Filters in the argument list match every other subsequent position, starting with current position |
| next* | next* stalemate |
Some subsequent (or current) position matches the argument filter |
| previous | previous (check check mate)previous (check+ mate) |
Filters in the argument list match preceding positions, starting with current position |
| previous2 | previous2 (check check mate)previous2 (check+ mate) |
Filters in the argument list match every other preceding position, starting with current position |
| previous* | previous* Ka-h8 |
Some subsequent (or current) position matches the argument filter |
Interaction with the current position
Each of these filters modifies the current position before its argument filters are evaluated. For example,previous sets the current position to every position equal to or a predecessor of the current position when the previous filter was first reached. After the current position is set to such a new position, the appropriate argument filter is evaluated at the new current position.
Of course, after these filters have finished matching their arguments, the current position is restored to what it was originally.
Interaction with variations
When thevariations parameter is set in the CQL header, these filters will search in both variations and the mainline. Otherwise, the filters only search in the mainline.
Counting
Each of these filters is countable and accepts an optional range argument following its name. The meaning of these ranges is described in the following table:
| filter name with range | example | description |
|---|---|---|
| next range | next 5 100 (check+ mate) |
Length of longest sequence of subsequent positions starting with current position matching arguments must be in range |
| next2 range | next2 5 100 (check+ mate) |
Length of longest sequence of every other subsequent (or current) positions matching arguments, starting with current position, must be in range |
| next* range | next* 10 1000 check |
Number of subsequent (or current) positions that matches the argument filter is in range |
| previous range | previous 5 100 (check+ initial) |
Length of longest sequence of preceding positions starting with current position matching arguments must be in range |
| previous2 range | previous2 5 100 (check+ initial) |
Length of longest sequence of every other preceding (or current) positions matching arguments, starting with current position, must be in range |
| previous* range | previous* 10 1000 check |
Number of previous (or current) positions that matches the argument filter is in range |
Because these filters can be counted, they can also be used as to sort the CQL output.