Inside the Architecture of a DC3 Compiler – Interpreter

DC3 is a complete, lightweight, Visual Basic-like (VB6) hybrid compiler and interpreter designed as an educational tool to teach developers how to build programming languages. Originally developed in Visual Basic 6, DC3 takes a simple, human-readable source language and compiles it into low-level bytecode, which is then executed line-by-line by an integrated Virtual Machine (VM) / Interpreter.

Building or understanding the DC3 pipeline follows a classic four-stage architectural pattern. The Architecture: Compiler vs. Interpreter

DC3 bridges the gap between pure compilation and pure interpretation by utilizing a two-part hybrid system:

The Frontend (Compiler): Scans, parses, and translates the raw VB-like script into intermediate bytecode.

The Backend (Interpreter/VM): Operates a virtual runtime stack that processes the bytecode instructions on the fly.

[ Source Code ] ──> ( Lexer ) ──> [ Tokens ] ──> ( Parser ) ──> [ AST / BNF ] │ [ Output/Result ] <── ( Virtual Machine ) <── [ Bytecode ] <── ( Code Gen ) Step-by-Step Implementation Guide Step 1: Lexical Analysis (The Lexer)

The lexer (or tokenizer) reads raw character strings from a text file and slices them into atomic units called Tokens.

Action: Create a scanner that loops through the text and tracks character pointers.

DC3 Specifics: The lexer categorizes data into three primary buckets: Identifiers: Variable names, functions, subroutines.

Literals: Numeric strings (integers, octals, hexadecimals, floats) and hardcoded text blocks.

Symbols/Operators: Arithmetic (+, -, *), VB comparisons (<=, <>), and inline modifications (+=, ++). Step 2: Syntax Analysis (The Parser)

The parser consumes the linear token stream and verifies that it complies with the structural grammar rules specified in the Backus-Naur Form (BNF) definition file of DC3.

Action: Build an Abstract Syntax Tree (AST)—a nested hierarchy where nodes represent structural actions (e.g., loops, conditionals) and leaves represent literals.

DC3 Specifics: The parser enforces static code limits. It strictly evaluates required elements, such as ensuring parentheses wrap all function/subroutine calls. It handles operator precedence natively via the traditional VB6 hierarchy. Step 3: Code Generation (Bytecode Compilation)

Unlike basic tree-walking interpreters that execute the AST directly, DC3 converts the tree layout into optimized bytecode operations.

Action: Flatten the hierarchical AST nodes into sequential, low-level operational codes (Opcodes).