A.31 library(varnumbers): Utilities for numbered terms

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.

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.

[det]numbervars(+Term)

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

See also

numbervars/3, numbervars/4

[det]varnumbers(+Term, -Copy)

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

[det]varnumbers(+Term, +Start, -Copy)

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

[det]max_var_number(+Term, +Start, -Max)

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

author

Vitor Santos Costa

Compatibility

YAP