Availability:built-in
clause(:Head,
?Body, ?Reference)Equivalent to clause/2,
but unifies Reference with a unique reference to the clause
(see also assert/2, erase/1).
If Reference is instantiated to a reference the clause's head
and body will be unified with Head and Body. The Reference
is a
blob (see section
12.4.10), which implies it is subject to
atom garbage collection. The Reference provides safe
access to the clause while it exists and generates a reliable
existence_error exception after the clause has been erased.