- Reference manual
$VAR(N), where N is the number of the variable. Counting starts at Start. End is unified with the number that should be given to the next variable.bugOnly tagged integers are supported (see the Prolog flag max_tagged_integer). This suffices to count all variables that can appear in the largest term that can be represented, but does not support arbitrary large integer values for Start. On overflow, a
representation_error(tagged_integer)exception is raised. The example below illustrates this. Note that the toplevel prints
'$VAR'(0)as A due to the
numbervars(true)option used to print answers.
?- Term = f(X,Y,X), numbervars(Term, 0, End), write_canonical(Term), nl. f('$VAR'(0),'$VAR'(1),'$VAR'(0)) Term = f(A, B, A), X = A, Y = B, End = 2.