JavaScript-Style Calculator

A powerful command-line calculator built in Haskell that supports JavaScript-style variable declarations and arithmetic expressions with proper operator precedence.

🚀 Features

• JavaScript Syntax: Familiar let and const declarations
• Decimal Arithmetic: Proper floating-point calculations (35/2 = 17.5)
• Variable Storage: Variables persist throughout the session
• Operator Precedence: Follows mathematical rules (*, / before +, -)
• Error Handling: Division by zero and undefined variable protection
• Interactive REPL: Real-time expression evaluation
• Comments Support: // line comments and /* */ block comments

📋 Supported Syntax

Variable Declarations

let x = 10;           // Variable declaration
const pi = 3.14159;   // Constant declaration  
z = x + y;            // Regular assignment

Mathematical Operations

addition = 5 + 3;           // Addition: 8
subtraction = 10 - 4;       // Subtraction: 6
multiplication = 6 * 7;     // Multiplication: 42
division = 35 / 2;          // Division: 17.5
precedence = 5 + 3 * 2;     // Precedence: 11 (not 16)
parentheses = (5 + 3) * 2;  // Parentheses: 16

🛠️ Installation

Prerequisites

• Stack (Haskell build tool)
• Git

Build from Source

# Clone the repository
git clone https://github.com/yourusername/js-calculator.git
cd js-calculator

# Build with Stack
stack build

# Run the calculator
stack exec js-add

Quick Start

# Interactive mode
stack exec js-add

# Single expression
echo "let result = 35 / 2" | stack exec js-add

🎯 Usage Examples

Interactive Session

$ stack exec js-add
JavaScript-Style Calculator!
Supports: +, -, *, /, variables, decimals, and JavaScript syntax

calc> let x = 10;
Let declaration: x = 10.0
Result: x = 10.0

calc> let y = 20;
Let declaration: y = 20.0
Result: y = 20.0

calc> result = (x + y) / 2;
Assignment: result = ((10.0 + 20.0) / 2.0)
Result: result = 15.0

calc> const pi = 3.14159;
Const declaration: pi = 3.14159
Result: pi = 3.14159

calc> area = pi * 5 * 5;
Assignment: area = ((3.14159 * 5.0) * 5.0)
Result: area = 78.53975

calc> quit
Goodbye!

Standalone Executable

A pre-built executable with batch launcher is available in the Calculator-Standalone/ folder:

• Double-click Start Calculator.bat for guided startup
• Or run JavaScript-Calculator.exe directly

🏗️ Architecture

Parser (Megaparsec)

• Lexical Analysis: Tokenizes JavaScript-style syntax
• Syntax Analysis: Builds Abstract Syntax Tree (AST)
• Operator Precedence: Handles mathematical precedence correctly

Evaluator

• Environment: Maps variable names to values
• Type Safety: Uses Maybe for error handling
• Functional Style: Clean applicative operations

REPL

• Interactive Loop: Read-Eval-Print-Loop
• Error Recovery: Continues after parse/evaluation errors
• EOF Handling: Graceful exit on input end

🔧 Technical Details

Built With

• Language: Haskell (GHC 9.10.3)
• Parser: Megaparsec library
• Build Tool: Stack
• Dependencies:
  • megaparsec - Parser combinators
  • text - Efficient text processing
  • containers - Data structures
  • parser-combinators - Expression parsing

Project Structure

js-calculator/
├── src/
│   └── Main.hs              # Main calculator implementation
├── Calculator-Standalone/    # Pre-built executables
├── js-add.cabal            # Package configuration
├── stack.yaml              # Stack configuration
├── README.md               # This file
└── LICENSE                 # BSD3 License

🧪 Development

Running Tests

# Build and test
stack build --test

# Run specific tests
stack test

Code Quality

• Zero Warnings: Clean compilation
• Haddock Documentation: Comprehensive API docs
• Type Safety: Leverages Haskell's type system
• Functional Style: Immutable data structures

🤝 Contributing

1. Fork the repository
2. Create a feature branch (git checkout -b feature/amazing-feature)
3. Commit your changes (git commit -m 'Add amazing feature')
4. Push to the branch (git push origin feature/amazing-feature)
5. Open a Pull Request

Development Setup

# Clone your fork
git clone https://github.com/yourusername/js-calculator.git

# Install dependencies
stack build --dependencies-only

# Run in development mode
stack ghci

📝 License

This project is licensed under the BSD3 License - see the LICENSE file for details.

🙏 Acknowledgments

• Megaparsec library for excellent parser combinators
• Stack for reliable Haskell builds
• Haskell Community for the amazing ecosystem

🐛 Known Issues

• Variables are session-only (not persistent between runs)
• No support for functions or complex data types
• Limited to basic arithmetic operations

🚧 Future Enhancements

• Mathematical functions (sin, cos, sqrt, etc.)
• Variable persistence to file
• Multi-line expressions
• Function definitions
• More JavaScript syntax (if/else, loops)
• Web interface

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Made with ❤️ and Haskell | Perfect for learning parser techniques!