FOOL Compiler

A compiler for FOOL (Functional Object-Oriented Language), developed for the course Linguaggi Compilatori e Modelli Computazionali — MSc in Computer Science and Engineering, University of Bologna (UNIBO).

Authors

• Alex Santini
• Roberto Pisu
• Alessandro Torelli

About the Language

FOOL is a small functional and object-oriented language supporting:

• Primitive types: int, bool
• Variables and functions with local declarations (let ... in)
• Classes with single inheritance (class ... extends ...)
• Methods and method dispatch via dot notation (obj.method(...))
• Object instantiation (new ClassName(...))
• Null reference and null-equality checks
• Control flow: if ... then { ... } else { ... }
• Arithmetic and logical operators: +, -, *, /, &&, ||, !
• Comparison operators: ==, >=, <=
• Print statement

Project Structure

.
├── compiler/           # Front-end and code generation
│   ├── FOOL.g4         # ANTLR4 grammar for FOOL
│   ├── AST.java        # Abstract Syntax Tree node definitions
│   ├── ASTGenerationSTVisitor.java    # ST → AST visitor
│   ├── SymbolTableASTVisitor.java     # Symbol table construction
│   ├── TypeCheckEASTVisitor.java      # Type checker
│   ├── PrintEASTVisitor.java          # AST pretty-printer
│   ├── CodeGenerationASTVisitor.java  # Code generator (SVM assembly)
│   ├── TypeRels.java   # Type relation helpers (subtyping)
│   ├── STentry.java    # Symbol table entry
│   ├── Test.java       # Main entry point
│   ├── exc/            # Compiler exceptions
│   └── lib/            # Base visitor classes and utilities
├── svm/                # Stack Virtual Machine
│   ├── SVM.g4          # ANTLR4 grammar for SVM assembly
│   └── ExecuteVM.java  # SVM interpreter
├── lib/
│   └── antlr-4.13.1-complete.jar   # ANTLR4 runtime
└── prova.fool          # Example FOOL program

Compilation Pipeline

1. Lexing & Parsing — ANTLR4 tokenises and parses the source file into a parse tree using FOOL.g4.
2. AST Generation — ASTGenerationSTVisitor converts the parse tree into an AST.
3. Symbol Table Analysis — SymbolTableASTVisitor resolves identifiers and builds the enriched AST (EAST).
4. Type Checking — TypeCheckEASTVisitor verifies type correctness, supporting subtyping and OOP dispatch rules.
5. Code Generation — CodeGenerationASTVisitor emits assembly code for the Stack Virtual Machine.
6. Assembly & Execution — The SVM assembles and executes the generated .asm file.

Requirements

• Java 11 or higher
• ANTLR 4.13.1 (included in lib/antlr-4.13.1-complete.jar)

How to Run

1. Compile the project

javac -cp lib/antlr-4.13.1-complete.jar compiler/*.java compiler/lib/*.java compiler/exc/*.java svm/*.java

2. Run the compiler on a .fool file

Place your source file (e.g. prova.fool) in the project root, then run:

java -cp .:lib/antlr-4.13.1-complete.jar compiler.Test

On Windows, replace : with ; in the classpath:

java -cp ".;lib/antlr-4.13.1-complete.jar" compiler.Test

The compiler will:

• Report any lexical, syntax, symbol-table, and type errors.
• If the front-end is error-free, emit prova.fool.asm and immediately run it on the SVM.

Example

The included prova.fool demonstrates class inheritance and method overriding with a BankLoan / MyBankLoan hierarchy:

let

  class Account (money:int) {
    fun getMon:int () money;
  }

  class TradingAcc extends Account (invested:int) {
    fun getInv:int () invested;
  }

  ...

  var bl:BankLoan = new MyBankLoan(new TradingAcc(50000,40000));
  var myLoan:Account = bl.openLoan(myTradingAcc);

in print(if (myLoan==null) then {0} else {myLoan.getMon()});