A flow-controller is an immutable object. Whenever an method, that may change
the internal state of the controller, is invoked, a new instance of the
controller is returned.
author: Thomas Morgner
Activates expressions that compute running values. This does not activate
precomputed expressions.
Parameters: expressions - throws: DataSourceException -
Returns the current expression slots of all currently active expressions.
(Maybe we should limit the access to the name and value of the expression
instead?)
throws: DataSourceException -