nb_set_shared_val/2¶

"nb_set_shared_val(+ Name, + Value" )

` Associates the term Value with the atom Name, but sharing non-backtrackable terms. This may be useful if you want to rewrite a global variable so that the new copy will survive backtracking, but you want to share structure with the previous term.

The next example shows the differences between the three built-ins:

~~~~~
?-
nb_setval(a,a(_)),nb_getval(a,A),nb_setval(b,t(C,A)),nb_getval(b,B).
A = a(_A), B = t(_B,a(_C)) ?

?-
nb_setval(a,a(_)),nb_getval(a,A),nb_set_shared_val(b,t(C,A)),nb_getval(b,B).

?-
nb_setval(a,a(_)),nb_getval(a,A),nb_linkval(b,t(C,A)),nb_getval(b,B).
A = a(_A),
B = t(C,a(_A)) ?
~~~~~

`