Pascal Language Compiler and Interpreter

A Java-based compiler and interpreter for a Pascal-like programming language that supports compilation to MIPS assembly code.

Features

• Interpreter Mode: Execute programs directly with immediate output
• MIPS Compiler: Generate MIPS assembly code for hardware execution
• Supports variables, arithmetic operations, control structures (IF/THEN, WHILE), and procedure calls

Compilation

Compile all source files:

javac parser/*.java ast/*.java scanner/*.java environment/*.java emitter/*.java

Usage

Running the Interpreter

java parser.ParserTester [filename]

• Executes the program and displays output immediately
• Default file: parserTest9.txt (if no filename provided)
• Input files should have .txt extension (omit extension in command)

Running the MIPS Compiler

java parser.MIPSCompiler [filename] 

• Compiles program to MIPS assembly code
• Generates [filename]MIPSCodeGen.asm output file
• Default file: parserTest9.txt (if no filename provided)

How It Works

1. Scanner Phase

• Tokenizes input source code into lexical tokens
• Handles keywords (VAR, BEGIN, END, IF, WHILE, etc.), operators, identifiers, and numbers

2. Parser Phase

• Uses recursive descent parsing to build an Abstract Syntax Tree (AST)
• Implements context-free grammar rules for the Pascal-like language
• Creates nodes for statements, expressions, and declarations

3. Execution/Compilation Phase

Interpreter Mode:

• Traverses AST and executes nodes directly using visitor pattern
• Maintains runtime environment for variable storage and scope management

MIPS Compiler Mode:

• Generates MIPS assembly instructions by traversing AST
• Uses stack-based expression evaluation
• Produces optimized assembly code with proper register allocation

Language Syntax

VAR x, y;
BEGIN
    x := 10;
    y := x + 5;
    WRITELN(y);
    IF x > 5 THEN WRITELN(x);
    WHILE x > 0 DO
    BEGIN
        WRITELN(x);
        x := x - 1;
    END;
END;
.

Example Usage

# Compile all files
javac parser/*.java ast/*.java scanner/*.java environment/*.java emitter/*.java

# Run interpreter
java parser.ParserTester parserTest1

# Generate MIPS code
java parser.MIPSCompiler parserTest1