SetTVLink

The SetTVLink is an evaluatable Link that can be used to update the TruthValue on a given Atom, given some source that provides a TruthValue. Such sources include other Atoms, in which case the TV is copied, or it may be a PredicateFormula or DynamicFormula, which compute a new TV, or a GroundedPredicateNode, which can call back into scheme or python to obtain a truth value.

This is generalized by the SetValueLink, which performs the same actions, but for generic Values.

Examples

Transfer the TruthValue from "foo" to "bar" ... copy it.

(cog-execute!
   (SetTV
      (Concept "bar")
      (TruthValueOf (Concept "foo"))))

Compute a TruthValue, using formulas.

(cog-execute!
   (SetTV
      (Concept "bar")
      (Times
         (TruthValueOf (Concept "foo"))
         (TruthValueOf (Concept "foo")))))

Use a GroundedPredicate to provide a truth value (one may also use a PredicateFormula, a DefinedPredicate or a DynamicFormula, as well).

(define (reddish-tv X Y)
   (SimpleTruthValue 
      (- 1 (* (cog-mean X) (cog-mean Y)))
      (* (cog-confidence X) (cog-confidence Y))))

(cog-execute!
   (SetTV
      (Concept "martian rock")
      (GroundedPredicate "scm: reddish-tv")
      (List (Concept "A") (Concept "B")))

A detailed exploration can be found in the /examples/atomspace/flows.scm file.