checks whether a key is member of the blackboard.
Blackboards are collections of (Key,Value) tuples. bb_contains_key/2 allows to retrieve the Key part of the blackboard.
If Key is not a free variable then bb_contains_key/2 succeeds if the blackboard Board contains the key Key.
If Key is a free variable then by backtracking bb_contains_key/2
lists all keys which are elements of the blackboard Board.
Board blackboard Key ground term
Assume there exists a blackboard 'blackboard' with elements (100, abc), (101, element101), (102, abc).
| bb_contains_key(blackboard, 100). | Succeeds. |
| bb_contains_key(blackboard, X). | Succeeds three times with substitution
X <- 100 X <- 101 X <- 102 |
This predicate is not part of the ISO-Prolog Standard.