The =>/2 construct is handled by the low-level compiler if
no
guard is present. If a guard is present it is currently
compiled into the construct below. The Picat ?=>/2 neck
operator is like
=>/2, but does not commit to this rule. We are not
yet sure whether or not SWI-Prolog will remain supporting
?=>/2.182?=>/2
is currently implemented but not defined as an operator.
Head ?=> Guard, !, Body.
The main consequence is that clause/2
cannot distinguish between a normal clause and a =>/2 clause.
In the current implementation it operates on both without distinguishing
the two. This implies e.g.,
cross referencing still works. Meta interpretation however does
not work. In future versions clause/2
may fail on these rules. As an alternative we provide rule/2,3.
- rule(:Head,
-Rule)
- rule(:Head,
-Rule, -Ref)
- True when Rule is a rule/clause that implements Head.
Rule is a complete rule term. For a normal clause this is a
term
Head :- Body and for a single sided unification rule
it is a term Head => Body.
