varnumbers.pl -- Utilities for numbered terms

This library provides the inverse functionality of the built-in numbervars/3. Note that this library suffers from the known issues that '$VAR'(X) is a normal Prolog term and, -unlike the built-in numbervars-, the inverse predicates do not process cyclic terms. The following predicate is true for any acyclic term that contains no '$VAR'(X), integer(X) terms and no constraint variables:

always_true(X) :-
      copy_term(X, X2),
      numbervars(X),
      varnumbers(X, Copy),
      Copy =@= X2.

See also

- numbervars/4, =@=/2 (variant/2).

Compatibility

- This library was introduced by Quintus and available in many related implementations, although not with exactly the same set of predicates.

 numbervars(+Term) is det

Number variables in Term using $VAR(N). Equivalent to numbervars(Term, 0, _).

See also

- numbervars/3, numbervars/4

 varnumbers(+Term, -Copy) is det

Inverse of numbervars/1. Equivalent to varnumbers(Term, 0, Copy).

 varnumbers(+Term, +Start, -Copy) is det

Inverse of numbervars/3. True when Copy is a copy of Term with all variables numbered >= Start consistently replaced by fresh variables. Variables in Term are shared with Copy rather than replaced by fresh variables.

Errors

- domain_error(acyclic_term, Term) if Term is cyclic.

Compatibility

- Quintus, SICStus. Not in YAP version of this library

 max_var_number(+Term, +Start, -Max) is det

True when Max is the max of Start and the highest numbered $VAR(N) term.

author

- Vitor Santos Costa

Compatibility

- YAP

 varnumbers_names(+Term, -Copy, -VariableNames) is det

If Term is a term with numbered and named variables using the reserved term '$VAR'(X), Copy is a copy of Term where each '$VAR'(X) is consistently replaced by a fresh variable and Bindings is a list X = Var, relating the X terms with the variable it is mapped to.

See also

- numbervars/3, varnumbers/3, read_term/3 using the variable_names option.