reactivation_nested_var.chr

:- module(reactivation_nested_var, [go_bare/2, go_nested/2]).
:- use_module(library(prelude)).

:- chr_constraint go_bare(any, any), go_nested(any, any),
                  pb(any), qb(any), pn(any), qn(any).

% Bare-variable argument (control): pb observes Y directly, so binding
% Y in the setup body reactivates pb and `fire_bare` runs, giving R = 7.
setup_bare @ go_bare(R, Y) <=> pb(Y), qb(R), Y = 1.
fire_bare  @ pb(X), qb(R) <=> X == 1 | R = 7.

% Variable nested several levels deep inside a compound argument
% (a list within a list): pn must observe the nested Y so that binding
% Y reactivates it and `fire_nested` runs. Regression test for the
% omega-r selective-reactivation bug where a stored constraint did not
% observe variables nested in compound arguments, leaving R unbound
% here. The extra nesting level also exercises the recursion depth on
% both backends.
setup_nested @ go_nested(R, Y) <=> pn([[Y]]), qn(R), Y = 1.
fire_nested  @ pn([[X]]), qn(R) <=> X == 1 | R = 7.