A%20Two-Dimensional%20Separation%20of%20Concerns%20for%20Compiler%20Construction

1
A Two-Dimensional Separation of Concernsfor
Compiler Construction

• Carl (Xiaoqing) Wu, Suman Roychoudhury,
• Barrett R. Bryant and Jeffrey G. Gray
• The University of Alabama at Birmingham, USA
• Marjan Mernik
• University of Maribor, Slovenia

2
Language Evolution

• During language evolution, compiler construction
  is usually performed along two dimensions
• The Inheritance pattern and the Visitor pattern
  are used to improve modularity in each case

adding new semantic operations (Visitor)
defining new abstract syntax tree (AST) nodes
(Inheritance)
3
Inheritance Pattern (I)

• A pure object-oriented approach based on AST
  nodes
• Declare an abstract super class for all AST nodes
  with virtual methods for node operations inside
  the class.
• Define a class for each AST node and implement
  the methods that inherit from the super node
  class.

4
Inheritance Pattern (II)

• Pros
• Easy to extend the grammar. Any new symbols can
  be added to the base grammar as a separated class
• Cons
• The semantic operations crosscut the various
  other class boundaries
• Adding a new operation requires an invasive
  change throughout the existing class hierarchy.

v
5
Visitor Pattern (I)

• Semantics operation oriented
• All the methods pertaining to one operation of
  the nodes are encapsulated into a single visitor
  unit
• Visitor is separated with node classes and can be
  freely added or deleted
• Object-Oriented Implementation
• Aspect-Oriented Implementation

6
Visitor Pattern (II)

• Object-Oriented Visitor

• Aspect-Oriented Visitor

7
Visitor Pattern (III)

• Pros
• Adding new semantics operations is easy
• Cons
• Operations belong to one AST node crosscut
  several visitor classes. Adding a new node to the
  existing class hierarchy will cause an invasive
  change to all of the visitors

v

8
Inheritance or Visitor
?
9
Compiler Matrix
Vertical modularization ? each column an class
? Inheritance Pattern Horizontal modularization
? each row an aspect ? Visitor Pattern
10
Pattern Transformation
11
A Simple Expression Language

• Syntax Grammar
• expression term binary_expression
• binary_expression sum difference
• sum expression expression
• difference expression - expression
• term integer_literal real_literal
• Semantics operations
• Value evaluation
• Type checking
• Pretty print

12
Phase I Build AST Nodes
13
Phase II Adding Semantics Operations
14
Phase III Extending Syntax Grammar

• expression term binary_expression
  unary_expression
• binary-expression sum difference quotient
  product
• sum expression expression
• difference expression - expression
• quotient expression / expression
• product expression expression
• unary_expression - term
• term integer_literal real_literal
  parenthesized_expression
• parenthesized_expression (expression )

15
Phase III Extending Syntax Grammar
16
Aspect Weaving and Unweaving
17
A General Example

• Payroll System

18
Future Work

• More complex programming language designs
• Aspect weaving and unweaving
• Multiple visitor functions for one semantics
  operation of one class
• Attributes of aspects
• The pattern transformation approach for other
  patterns
• Observer
• Mediator
• Abstract Factory

19
Conclusion

• By exploring the essence of the compiler matrix,
  we developed an approach for compiler
  construction in two dimensions
• Based on pattern transformation
• Using object-orientation and aspect-orientation
• The pattern transformation approach can be also
  utilized in other software system development and
  extended to other patterns
• Multi-dimensional evolution needs exist in
  software development, no single design principle
  or pattern offers a panacea toward addressing
  problems of change evolution.
• Transformation techniques applied to design
  patterns offer an alternative to alleviating this
  problem.

20
Questions?