flex Expert System Toolkit - LPIS

9. Flex Predicates 155
spy_fact( ?Name )
Whenever a fact or an exception whose principal functor is Name is either
added to or removed from the workspace, this information is written to the
current output stream.
In particular, if Name is a variable then all fact and exception transactions
will be monitored.
Examples
spy_rule( ?Name )
spy_fact( likes ) .
spy_fact( dislikes ) .
Set a spypoint on the named rule. Whenever the forward chaining engine is
being traced (see spy_chain/0) and Name is considered as a potential rule
to fire, then the conditions associated with that rule are traced by the
debugger.
Example
spy_rule( prescribe_lomotil ) .
spy_slot( ?Attribute, ?Frame )
Set a spypoint on an Attribute of a Frame, such that whenever the slot
is updated the relevant information is displayed in the current output stream.
Examples
spy_slot( habitat, moby_dick ).
spy_slot( _, albino ).
spy_slot( temperature, _ ).
spy_slot( _, _ ).
sub_value( +Slot,+Term )
sub_value/2 can either be used to remove items from lists or to
decrement numbers.
The given Term is first dereferenced down to some Value. The Slot
should either be a compound term of the form @(Attribute,Frame) or
it is the name of a global variable, in which case the name of the frame to be
used is global.
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