Availability:built-in
numbervars(+Term,
+Start, -End)$VAR(N),
where N is the number of the variable. Counting starts at
Start. End is unified with the number that should
be given to the next variable.bugOnly tagged
integers are supported (see the Prolog flag max_tagged_integer).
This suffices to count all variables that can appear in the largest term
that can be represented, but does not support arbitrary large integer
values for Start. On overflow, a representation_error(tagged_integer)
exception is raised. The example below illustrates this.
Note that the toplevel prints '$VAR'(0) as A due
to the
numbervars(true) option used to print answers.
?- Term = f(X,Y,X),
numbervars(Term, 0, End, [singleton(true)]),
write_canonical(Term), nl.
f('$VAR'(0),'$VAR'('_'),'$VAR'(0))
Term = f(A, _, A),
X = A,
Y = B,
End = 2.
See also the numbervars option to write_term/3
and numbervars/4.