[kepler-dev] Type error with NondeterministicMerge under Kepler

[Norbert Podhorszki]

Hi,

We have hit a type problem in Kepler with Bruce while playing with the 
NondeterministicMerge actor and then found an interesting and annoying 
difference between the type checking in Kepler and Ptolemy. Now we know 
how to solve the problem by specifying the types manually but still we 
wonder if this is a bug or just a side-effect how Kepler stores actors in 
its xml.

The model
=========
In the attached examples, there is a simple pipeline

    Record Assembler  ---  Nondet.Merge  ---  Record Disassembler

i.e. we want to push record tokens through the model.
The Ptolemy version (built under Ptolemy) works as expected, even under 
Kepler. The Kepler version, however, does not run because we get an error 
from the type checker:

     ptolemy.kernel.util.InternalErrorException: Type resolution failed because
     of an error during type inference
        in .NondetMerge_TypeError_Kepler
     Because:
     Invalid type for input port
        in .NondetMerge_TypeError_Kepler.Record Disassembler

The difference
==============
Replacing the NondeterministicMerge entity manually in the Kepler workflow 
xml with the entity in the Ptolemy model (see 
NondetMerge_TypeError_KP.xml), the error disappears.

The difference between the two entities is that while Ptolemy only 
declares the class
     <entity name="NondeterministicMerge" class="ptolemy.domains.pn.kernel.NondeterministicMerge">
         <property name="_location" class="ptolemy.kernel.util.Location" value="[350.0, 160.0]">
         </property>
     </entity>

Kepler enumerates the ports and their types as well, which, in the case of 
NondeterministicMerge are 'general'.
     <entity name="NondeterministicMerge" class="ptolemy.domains.pn.kernel.NondeterministicMerge">
         <property name="_location" class="ptolemy.kernel.util.Location" value="[350.0, 160.0]">
         </property>
         <port name="input" class="ptolemy.actor.TypedIOPort">
             <property name="input"/>
             <property name="multiport"/>
             <property name="_type" class="ptolemy.actor.TypeAttribute" value="general">
             </property>
         </port>
         <port name="output" class="ptolemy.actor.TypedIOPort">
             <property name="output"/>
             <property name="_type" class="ptolemy.actor.TypeAttribute" value="general">
             </property>
         </port>
     </entity>

The manual solution
===================
AFAIK, the type checker then will not climb down from the top 'general' to 
find that always just RecordType tokens will be emitted. If we set the 
types of the input and output ports of the actor to our specific record 
type in the GUI, then it works again.

Then why do we complain?
========================
First of all we wonder if this is necessary to be this way in Kepler.
Second, how many actors may be there that can bring such a surprise to the 
developer.

Third, no one should wonder that the beginner developer is completely lost 
since he does not understand the Ptolemy error message, and actually he 
made nothing wrong, so after crawling through the hopeless route down to 
hell, desperately looks for advise from an experienced developer, who also 
has no idea. Lots of trials, small test examples and changing from Kepler 
to Ptolemy for counter-testing reveals what's wrong (since the error 
message does not reveal it) and finally the solution come. Since the 
beginner developer committed nothing wrong, it would be good not to get 
into such situation.

Oh and yes, I know that he should not go with the nondet merge at all and 
I will help him to create a DDF solution for his problem. Eventually. ;-)

Best regards
Norbert


      Norbert Podhorszki
    ------------------------------------
      University of California, Davis
      Department of Computer Science
      1 Shields Ave, 2236 Kemper Hall
      Davis, CA 95616
      (530) 752-5076
      pnorbert at cs.ucdavis.edu
      ----------------------------------
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