Simple Arithmetic Expression Parser in Haskell

This project implements a basic arithmetic expression parser and evaluator using a recursive descent approach.

It supports:

• Single-digit integers
• Addition (+)
• Multiplication (*)
• Parentheses ( ) for grouping
• Operator precedence (* binds tighter than +)

📦 Project Structure

• src/Main.hs — contains the parser and evaluator logic
• Main.main runs test cases and prints results

🚀 Running the Project

Make sure you have Stack installed.

stack run

This will compile and run the project, showing results of several example expressions.

🧪 Example Expressions

2+3*4         => 14
(1+2)*3       => 9
3*(1+2+4)     => 21

📚 How It Works

The parser uses three mutually recursive functions:

• expr handles addition
• term handles multiplication
• factor handles digits and parentheses

This structure enforces correct operator precedence naturally.

✅ Next Steps (Ideas)

• Add subtraction and division
• Handle multi-digit numbers, and handle whitespace
• Remove unsafe use of head and tail
• Tokenizer
• Parser Monad/Combinator
• Add error messages or AST building