Calculator

A simple mathematical expression calculator built with Go as a learning project for implementing recursive descent parsers.

What it does

Evaluates mathematical expressions with proper operator precedence:

• Basic operations: +, -, *, /
• Parentheses for grouping: (1 + 2) * 3
• Handles operator precedence correctly: 1 + 2 * 3 = 7
• Advanced operations like sin, tan, cos

Grammar

I decided to implement the following EBNF grammar, since it elimates left-recursion in a more efficent way then context-free grammars do.

exp     -> product (('+' | '-') product)*
product -> factor (('*' | '/') factor)*
factor  -> (sin|cos|tan)? '(' exp ')' |NUMBER

Usage

git clone https://github.com/driemtax/Calculator.git
cd Calculator
go run cmd/calculator/main.go

Or use as a library:

import "github.com/driemtax/Calculator/pkg/calculator"

result, err := calculator.Evaluate("(1 + 2) * 3")
// result: 9.0

Another Example, where i used it as a cli tool in my own shell implementation

Project Structure

Calculator/
├── cmd/calculator/main.go       # CLI entry point
├── pkg/
│   ├── calculator/              # Main API
│   ├── scanner/                 # Tokenization
│   ├── parser/                  # Recursive descent parser
│   └── arithmetics/             # Basic math operations

Learning Goals

This project demonstrates:

• Lexical Analysis: Breaking strings into tokens
• Recursive Descent Parsing: Implementing a grammar with proper precedence
• Go Project Structure: Clean package organization
• Error Handling: Meaningful error messages for invalid input

Built purely with Go's standard library - no external dependencies.