Symbolic Logic:Programming:Program Model

A "Program Model" is a representation of a program as objects.

In Object Oriented Programming the domain we wish to describe is modeled as objects. This gives an object representation of the domain we choose. For example, applying OOP to the trading domain gives a Trading Model. Orders, Executions and Trades are modelled as objects.

Applying Object Oriented Programming to programs gives a Program Model. Classes, Functions, Function Calls, and Variables are modelled as objects.

Contents 1 History 2 Purpose 3 Easy Implementation 3.1 Class Constants 3.2 Built in functions 3.3 Example

[edit] History

When a program is compiled, internally the compiler must implicitly construct a model of the program. However this model is thrown away. All the compiler and linker finally produces is the executable. The programmer only wants the program to execute correctly. The programmers target audience is the user running the program.

The programmer makes compromises in writing the program between really general solutions that would run slowly, and specific solutions that run fast, but have limitted applicability.

[edit] Purpose

The purpose of the Program Model is to add another level of processing, before the program is turned into an executable. This level performs analysis on the program prior to generating the executable. The most easy to implement analysis is partial evaluation. There are many other kinds of analysis that may be done.

[edit] Easy Implementation

Starting with a basic set of classes to represent the program objects,

Program Model Classes

Name	Description	Inherits	Methods
PMClass	A class that represents a class	PMObject	IsA, HasFunction
PMFunction	A class that represents a function	PMObject	Parameter, SetBody.
PMCall	A class that represents a call to a function	PMValue	SetFunction, Parameter.
PMVariable	A class that represents a variable	PMValue
PMConstant	A class that represents a constant expression (like 1 or "some text").	PMValue
PMValue	A class that represents a value.	PMObject	The pure operators (+, -, *, /).

In a language like C++ that has operators it is possible to write expressions that look like the calculation of a value, which instead return a Program Model Object that represents the calculation.

[edit] Class Constants

Constants of type PMClass.  ???? How high level should these be (e.g precision) ????

• PMInteger
• PMReal

[edit] Built in functions

• PMIf

[edit] Example

 PMClass *math = new PMClass("math");
 PMVariable *n = new PMVariable(PMInteger);
 PMFunction *factorial = math->HasFunction("factorial", PMInteger)->Parameter(n)
                         ->SetBody( PMIf(n == 0, new PMConstant(1), n * factorial->parameter(n-1)) );