
excl(?Var, ++Excl)

   Exclude the element Excl from the domain of Var.

Arguments
   Var                 Integer variable or integer
   Excl                Value to exclude

Type
   library(ic_kernel)

Description

   Primitive for excluding an element from the domain of an integer
   variable.  The call may fail (when Var is the same integer as Excl),
   succeed (possibly updating the variable's domain), or instantiate the
   variable (when Excl was one of only two domain elements left).

   Note that this predicate is intended for use only in implementing
   constraint propagators, and should not be called from ordinary user code
   (use ic:(Var =\= Excl) instead).  It differs from the usual constraint
   predicates with respect to the execution of delayed goals.  If the call
   to excl/2 results in a domain change, any delayed goals suspended on that
   change will be scheduled for execution, as normal.  However, excl/2 does
   not call the woken goal scheduler (wake/0), so these goals may not be
   executed immediately.  (It is possible that under some circumstances the
   goals will be executed, if wake/0 is called indirectly - one example
   would be by the unify handler if the variable becomes ground - but this
   should not be relied upon.)  To ensure that the goals are eventually
   executed, the caller should arrange for wake/0 to be called at some
   appropriate point in the subsequent execution.  Please see the "Advanced
   Control Features" section of the User Manual for more information about
   woken goal management.


Examples
   [eclipse 3]: X :: 0..10, excl(X, 4).
X = X{[0 .. 3, 5 .. 10]}
Yes (0.00s cpu)

[eclipse 4]: X :: [4, 6], excl(X, 4).
X = 6
Yes (0.00s cpu)


See Also
   excl_range / 3
