10.10.9.2 Reflection Predicates
The constraint solving method needs access to information about the
current domains of variables. This is provided by the following
predicates, which are all constant time operations.
fd_var(
?X)

Checks that X is currently an unbound variable that is known to
the CLPFD solver.
fd_min(
?X,
?Min)

where X is a domain variable (or an integer). Min is
unified with the smallest value in the current domain of X, i.e.
an integer or the atom
inf
denoting minus infinity.
fd_max(
?X,
?Max)

where X is a domain variable (or an integer). Max is
unified with the upper bound of the current domain of X, i.e. an
integer or the atom
sup
denoting infinity.
fd_size(
?X,
?Size)

where X is a domain variable (or an integer). Size is
unified with the size of the current domain of X, if the domain is
bounded, or the atom
sup
otherwise.
fd_set(
?X,
?Set)

where X is a domain variable (or an integer). Set is
unified with an FD set denoting the internal representation of the
current domain of X; see below.
fd_dom(
?X,
?Range)

where X is a domain variable (or an integer). Range is
unified with a ConstantRange (see Syntax of Indexicals)
denoting the current domain of X.
fd_degree(
?X,
?Degree)

where X is a domain variable (or an integer). Degree is
unified with the number of constraints that are attached to X.
Please note: this number may include some constraints that have
been detected as entailed. Also, Degree is not the number of
neighbors of X in the constraint network.
The following predicates can be used for computing the set of variables
that are (transitively) connected via constraints to some given
variable(s).
fd_neighbors(
+Var,
Neighbors)

Given a domain variable Var, Neighbors is the set of
variables that can be reached from Var via constraints
posted so far.
fd_closure(
+Vars,
Closure)

Given a list Vars of domain variables, Closure is the set of
variables (including Vars) that can be transitively reached via
constraints posted so far. Thus,
fd_closure/2
is the transitive
closure of fd_neighbors/2
.
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