Title:
More Flexible Software By Favoring Implicit Calls
and Communication over Explicit Calls and Communication

Speaker: Karl Lieberherr, CCIS, PRL, Northeastern University

Abstract:
Adaptive Programming (AP) has promoted the idea
of calling methods indirectly through traversals.
Aspect-Oriented Programming (AOP) took this to the next level
by calling methods indirectly through general programs,
not just traversals.  Both AP and AOP are departures from the traditional
functional and object-oriented approaches that suffer from two major problems:
they explicitly mention by name the subterms or subobjects that
need to be traversed (explicit traversal problem)
and they explicitly mention parameters that
are passed down to subterms or subobjects, whether or not they are relevant
to the current term or object (explicit argument problem).
The reason for the two problems is a
low-level use of "follow the structure" or "follow the grammar".

We propose two new approaches to implicit calls and communication.

The first approach, called AP-F, is a functional 
approach that parameterizes the traversal with three kinds of function
objects: transformers, builders and augmentors. 
The default traversal is implementing a builder.
Our current implementation of AP-F is called DemeterF and is provided 
as a Java library that heavily relies on reflection.
DemeterF includes a type checker that proves useful in debugging
the programs.

The second approach, called AP-P, is an interposition visitor
approach that relies on traversals and before/after methods.
An interposition visitor uses interposition variables that
facilitate implicit communication. Our current implementation
of AP-P is called DemeterP and relies on code generation using 
AspectJ.

We have successfully used DemeterF programs for refactoring
interpreters, compilers from the EoPL book by Friedman and Wand,
making the programs both simpler and more flexible.

Joint work with Bryan Chadwick, Ahmed Abdelmeged and Therapon Skotiniotis.

===
Possible Titles: 
Traversal Scoped Variables
Abstracting Over Transformations and Communication (in Traversal-Related Concerns)

Outline

1. Introduction
   Implicit versus explicit calls and communication
   Running Examples: evaluator, type checker, translator
2. AP-F
2.1 Dynamic join point model
2.2 Operational semantics
2.3 Type-checking
    Transformers
      Typing rule at object level
      Typing rule at class level
      Theorem from mp 8 linking the two
    Combiners
    Augmentors
2.4 Design Issues: From requirements to AP-F
2.5 Implementation
    DemeterF
    Example code
3. AP-P
   Interposition visitors
3.1 Dynamic join point model
3.2 Operational semantics
    Simulating Transforms and Combines.
    Parameterized Copy Visitor.
    Visitor Combination.
3.* Design Issues: From requirements to AP-P
3.* Implementation
    DemeterP
    Example code

4. Comparsion
5. Related Work
   SYB, Attribute Grammars, Functional Visitors
6. Experience Report