Internal patterns passed on evalution of a DefinedSchemaNode by a GroundedPredicateNode

[amebel]

Setup scheme file content

(clear)
(use-modules (opencog))
(use-modules (opencog exec))
(use-modules (opencog query))

(InheritanceLink
   (ConceptNode "OpenPsi: Energy" (stv 0.66960984 0.99999982))
   (ConceptNode "OpenPsi: Demand")
)

(InheritanceLink
   (DefinedSchemaNode "OpenPsi: Energy-action-rule-Default")
   (ConceptNode "opencog: action")
)

(MemberLink (stv 1 0.99999982)
   (DefinedSchemaNode "OpenPsi: Energy-action-rule-Default")
   (ConceptNode "OpenPsi: Energy" (stv 0.66960984 0.99999982))
)

(EvaluationLink
   (PredicateNode "OpenPsi: default_value")
   (ListLink
      (ConceptNode "OpenPsi: Energy" (stv 0.66960984 0.99999982))
      (NumberNode "0.710000")
   )
)

(DefineLink
   (DefinedPredicateNode "OpenPsi: demand-pattern")
   (PresentLink
      (InheritanceLink
         (VariableNode "Demand" (stv 0.96491325 0))
         (ConceptNode "OpenPsi: Demand")
      )
      (EvaluationLink
         (PredicateNode "OpenPsi: default_value")
         (ListLink
            (VariableNode "Demand" (stv 0.96491325 0))
            (VariableNode "default_value")
         )
      )
   )
)

(define z-dsn (DefinedSchemaNode "OpenPsi: Energy-action-rule-Default"))
(DefineLink
   z-dsn
   (BindLink
      (VariableList
         (TypedVariableLink
            (VariableNode "Demand" (stv 0.96491325 0))
            (TypeNode "ConceptNode")
         )
      )
      (AndLink
         (DefinedPredicateNode "OpenPsi: demand-pattern")
         (EqualLink
            (VariableNode "Demand" (stv 0.96491325 0))
            (ConceptNode "OpenPsi: Energy" (stv 0.66960984 0.99999982))
         )
      )
      (ExecutionOutputLink
         (GroundedSchemaNode "scm: foo")
         (ListLink
            (VariableNode "Demand" (stv 0.96491325 0))
         )
      )
   )
)

(define (foo node) node)

(define z-get
    (GetLink
       (TypedVariableLink
          (VariableNode "x")
          (TypeNode "DefinedSchemaNode")
       )
       (AndLink
          (MemberLink
             (VariableNode "x")
             (ConceptNode "OpenPsi: Energy" (stv 0.66960984 0.99999982))
          )
          (InheritanceLink
             (VariableNode "x")
             (ConceptNode "opencog: action")
          )
          (EvaluationLink
             (GroundedPredicateNode "scm: what?")
             (ListLink
                (VariableNode "x")
             )
          )
       )
    )
)

(define (what? dsn)
    (begin
        (display "\n------------------------------------------\n")
        (display "\nDefinedSchemaNode Expanded and passed to this function \n")
        (display dsn)
        (display "\n------------------------------------------\n")
        (display "\nExpected DefinedSchemaNode got\n")
        (display (cog-chase-link 'DefineLink 'DefinedSchemaNode dsn))
        (display "\n------------------------------------------\n")
        (display "\n#############################################\n")
        (stv 1 1)
    )
)

(define (test)
    (cog-execute! z-get)
)

(define (check)
    (cog-chase-link 'DefineLink 'BindLink z-dsn)
)

Trying to get the DefineSchemaNode

scheme@(guile-user)> (load "the-scheme-setup-file-from-above.scm")
....
scheme@(guile-user)> (test)

------------------------------------------

DefinedSchemaNode Expanded and passed to this function
(BindLink
   (VariableList
      (TypedVariableLink
         (VariableNode "Demand" (stv 0.96491325 0))
         (TypeNode "ConceptNode")
      )
   )
   (AndLink
      (DefinedPredicateNode "OpenPsi: demand-pattern")
      (EqualLink
         (VariableNode "Demand" (stv 0.96491325 0))
         (ConceptNode "OpenPsi: Energy" (stv 0.66960984 0.99999982))
      )
   )
   (VariableNode "Demand" (stv 0.96491325 0))
)

------------------------------------------

Expected DefinedSchemaNode got
()
------------------------------------------

#############################################
(SetLink
   (DefinedSchemaNode "OpenPsi: Energy-action-rule-Default")
)

The issue

If the BindLink was actually an expansion of the DefinedSchemaNode, then the Expected DefinedSchemaNode got lines of the output wouldn't have been an empty list. It seems, a BindLink that is created intermediately within the query-engine is passed instead.

Expected BindLink to be passed to the what? function is

scheme@(guile-user)> (check)
((BindLink
   (VariableList
      (TypedVariableLink
         (VariableNode "Demand" (stv 0.96491325 0))
         (TypeNode "ConceptNode")
      )
   )
   (AndLink
      (DefinedPredicateNode "OpenPsi: demand-pattern")
      (EqualLink
         (VariableNode "Demand" (stv 0.96491325 0))
         (ConceptNode "OpenPsi: Energy" (stv 0.66960984 0.99999982))
      )
   )
   (ExecutionOutputLink
      (GroundedSchemaNode "scm: foo")
      (ListLink
         (VariableNode "Demand" (stv 0.96491325 0))
         (NumberNode "5.000000")
      )
   )
)
)

[linas]

This is difficult to understand, but I think you were expecting what? to get z-dsn as the argument, and, instead, you got the result of (cog-execute! z-dsn) and are surprised by that.

The explanation for this is easy: when you (cog-execute! z-get), you have an AndLink of three items, one of which is

     (EvaluationLink
             (GroundedPredicateNode "scm: what?")
             (ListLink
                (VariableNode "x")))

In order to see if the AndLink is true, the pattern matcher must check to see if above is true. This is done in two steps: first, (VariableNode "x") is replaced by its grounding (which is z-dsn), then the EvaluationLink as a whole is evaluated. A side effect of that evaluation is that (cog-execute! z-dsn) is performed, and the result of that is passed to what?.

From what I can tell, what you need to do is to have this instead:

     (EvaluationLink
             (GroundedPredicateNode "scm: what?")
             (ListLink
                (DontExecLink (VariableNode "x"))))

and that will give you what you want. However, the DontExecLink doesn't exist yet.

Is this what you want to do? If so, then I guess that a DontExecLink could be created... (we need a better name for it)

[linas]

In scheme, DontExecLink is called syntax or quasisyntax .. I don't exactly like the name SyntaxLink but QuasiSyntaxLink makes it vaguely acceptable...

[amebel]

Yes, something like quasisyntax is what I wanted.

Another thing I don't get why (cog-execute! z-dsn) would return

(BindLink
   (VariableList
      (TypedVariableLink
         (VariableNode "Demand" (stv 0.96491325 0))
         (TypeNode "ConceptNode")
      )
   )
   (AndLink
      (DefinedPredicateNode "OpenPsi: demand-pattern")
      (EqualLink
         (VariableNode "Demand" (stv 0.96491325 0))
         (ConceptNode "OpenPsi: Energy" (stv 0.66960984 0.99999982))
      )
   )
   (VariableNode "Demand" (stv 0.96491325 0))
)

instead of

(SetLink 
     (ConceptNode "OpenPsi: Energy")
)

[linas]

ah yes, you are right ... the result of (cog-execute! z-dsn) is incoherent/wrong. Its related to bug #686 -- for historical reasons, you cannot "run" Bindlinks with cog-execute, you can only run them with cog-bind. Nonetheless, cog-execute! is being eager and blind, and tries to do something, anything, and it ends up finding the embedded ExecutionOutputLink, and it runs only that. This is a separate, distinct bug.

[linas]

I opened issue #705 do describe this bug. Do you want me to fix this muddled-puddle of issues? I'd probably fix #705 first, by making it partly do what #686 is saying. After that, would need to implement QuasiSyntaxLink. is there a better name for this?

[amebel]

Yes please, on fixing the muddled-puddle 😄

How about PassLink similar to python's pass https://docs.python.org/2.7/reference/simple_stmts.html#pass

[linas]

working on it now. Its causing a snowball of changes to occur.

[linas]

fixed in pull request #714

[amebel]

Thanks