XIDEK
Extensible Interpreter Development Kit

Implementation

• Introduction
• Support Code
• Compiling and Linking

Introduction

Since all of the interpreters are functionally interchangeable, a single main program, contained in driver\demo.cpp, suffices to demonstrate the host program interface for any of the interpreters.

The common symbol table mechanism used by the interpreters allows the values of variables to be both set and queried by the host program. Thus values can be initialized before a script is interpreted and results can be queried after execution. Since the symbol table is completely separate from the script interpreters, a given symbol table can be used with any number of scripts.

The symbol table actually consists of two separate objects, an AgDictionary<AgString> object which identifies variable names, and a Dataset object which contains a reference to the dictionary and a value for each variable in the dictionary. Any number of Dataset objects can share the same dictionary.

Organization of the Code

The modules fall into three basic classes: the language independent modules, which are found in the support directory, the CLL language dependent modules, which are found in the cll, and the PLL language dependent modules which are found in the pll directory. Each of these directories contains subdirectories as follows:

base

These directories contain all files required for implementing the baseline interpreters.

complex

These directories contain all files required for implementing the complex arithmetic examples.

array

These directories contain all files required for implementing the arrays and subscripts examples.

struct

These directories contain all files required for implementing the structures and objects examples.

function

These directories contain all files required for implementing the local function definition examples.

combine

These directories contain all files required for implementing the combined arrays, structures and functions examples.

• Common Definitions.
  The comdefs.h and comdefs.cpp files define the Value and Dataset classes as well as several other support classes. These classes are used in all four interpreters.

  The evaluation of expressions is entirely contained within the Value class. Thus, extending the computational range of any of the interpreters can be done simply by extending the Value class. To exemplify this capability, an extension to support complex arithmetic is documented here.

• Bytecode Interpreter Definitions.
  The opcodes.h, bcidefs.h and bcidefs.cpp files define a bytecode interpreter class, ScriptMethod, and the CodeFragment class which handles much of the work of creating bytecode. This module is used by both the Direct Compilation Interpreter and the Tree Compilation Interpreter.

• Abstract Syntax Tree Definitions.
  The opcodes.h, astdefs.h, and astdefs.cpp files define the structures used to represent abstract syntax trees. This module is used by both the Tree Execution Interpreter and the Tree Compilation Interpreter.

• Abstract Syntax Tree Execution Interpreter Module
  The same interpreter control module is used for both the CLL and PLL versions of the astxi interpreter architecture. The differences between the two interpreters are found entirely in the parsers.

• Abstract Syntax Tree Compilation Interpreter Module
  The same interpreter control module is used for both the CLL and PLL versions of the astci interpreter architecture. The differences between the two interpreters are found entirely in the parsers.

• The Direct Execution Parser
  This parser is the main interpreter module for the direct execution interpreter.

• The Direct Compilation Parser
  This parser is the compilation module for the direct compilation interpreter.

• Abstract Syntax Tree Parser.
  This parser is used to create an abstract syntax tree. It is used by both the Tree Execution Interpreter and the Tree Compilation Interpreter.

• Main Program
  The driver\demo.cpp file contains a simple command line main program which carries out the following operations:
  1. Reads a script file specified on the command line.
  2. Sets up an AgDictionary<AgString> object to serve as symbol dictionary.
  3. Adds some variables to the dictionary.
  4. Creates a Dataset object with a reference to the dictionary.
  5. Initializes some variables in the Dataset object.
  6. Invokes the interpreter, using the common interface.
  7. Sorts the variables in the dictionary.
  8. Prints out the name and value of each variable in the dictionary.

  This main program is intended only to demonstrate how an interpreter can be invoked from a host program. Since all the interpreters implement the same interface, this main program can be used with any of them.

• AnaGram Class Library
  The class library, AGCLIB1, is not, properly speaking, a part of the kit. AGCLIB1 is a simple, compact collection of classes designed to support AnaGram examples. The classes were designed from a minimalist point of view so that users can substitute the class library they prefer with as little difficulty as possible, should it be appropriate.

Compiling and Linking

Each of these directories contains subdirectories to segregate CLL and PLL interpreters. Each of these subdirectories in turn contains subdirectories for the baseline interpreters and for each of the extension examples.

Make files have been provided at each level of the directory structure. Thus, the nmake command when executed from the msvc directory uses Microsoft Visual C++ to make all 48 different interpreters. From the msvc\cll directory, the nmake command will make only the 24 CLL interpreters. From the msvc\cll\base directory, nmake will make only the four baseline CLL interpreters. In this latter directory, nmake can take an optional argument to make just one of the four baseline interpreters. The same structure is used for all six compilers supported.

The make files also run simple tests. The tests are found in the test\cll and test\pll directories. The test files are described here.

Note that if any changes are made to the AGCLIB1 class library, it should be rebuilt using the corresponding makefile. See here.

If you are using some other compiler, here are the modules you need to compile and link:

	Interpreter		Modules
	dxi		dxi.cpp comdefs.cpp demo.cpp
	dci		dci.cpp comdefs.cpp bcidefs.cpp demo.cpp
	astxi		astxi.cpp comdefs.cpp astdefs.cpp ast.cpp demo.cpp
	astci		astci.cpp comdefs.cpp bcidefs.cpp astdefs.cpp ast.cpp demo.cpp

Two modules belonging to the AGCLIB1 Class Library are also required:

• agabt.cpp
• agbstr.cpp