Book Image

Build Your Own Programming Language

By : Clinton L. Jeffery
Book Image

Build Your Own Programming Language

By: Clinton L. Jeffery

Overview of this book

The need for different types of computer languages is growing rapidly and developers prefer creating domain-specific languages for solving specific application domain problems. Building your own programming language has its advantages. It can be your antidote to the ever-increasing size and complexity of software. In this book, you’ll start with implementing the frontend of a compiler for your language, including a lexical analyzer and parser. The book covers a series of traversals of syntax trees, culminating with code generation for a bytecode virtual machine. Moving ahead, you’ll learn how domain-specific language features are often best represented by operators and functions that are built into the language, rather than library functions. We’ll conclude with how to implement garbage collection, including reference counting and mark-and-sweep garbage collection. Throughout the book, Dr. Jeffery weaves in his experience of building the Unicon programming language to give better context to the concepts where relevant examples are provided in both Unicon and Java so that you can follow the code of your choice of either a very high-level language with advanced features, or a mainstream language. By the end of this book, you’ll be able to build and deploy your own domain-specific languages, capable of compiling and running programs.
Table of Contents (25 chapters)
1
Section 1: Programming Language Frontends
7
Section 2: Syntax Tree Traversals
13
Section 3: Code Generation and Runtime Systems
21
Section 4: Appendix

Checking for undeclared variables

To find undeclared variables, check the symbol table on each variable that's used for assignment or dereferencing. These reads and writes of memory occur in the executable statements and the expressions whose values are computed within those statements. Given a syntax tree, how do you find them? The answer is to use tree traversals that look for IDENTIFIER tokens but only when they are in executable statements within blocks of code. To go about this, start from the top with a tree traversal that just finds the blocks of code. In Jzero, this is a traversal that finds the bodies of methods.

Identifying the bodies of methods

The check_codeblocks() method traverses the tree from the top to find all the method bodies, which is where the executable code is in Jzero. For every method declaration it finds, it calls another method called check_block() on that method's body:

method check_codeblocks()
   if sym == "MethodDecl...