THE EGG PROGRAMMING LANGUAGE

This is a simple programming language implementation based on the guide from Eloquent JavaScript Chapter 12. The book provides a basic level implementation. I've managed to a add on a few more features.

Features

• Simple Syntax: Everything is an expression
• Functions: First-class functions with closures
• Control Flow: if conditionals and while loops
• Variables: Variable definition and assignment
• Arrays: Built-in array support
• Comments: Line comments starting with #
• REPL: Interactive shell for testing

Architecture

The language implementation consists of several modules:

• parser.js - Converts source code into Abstract Syntax Tree (AST)
• evaluator.js - Executes the AST
• special-forms.js - Implements special syntax (if, while, define, etc.)
• environment.js - Defines built-in functions and global scope
• egg.js - Main module with CLI and REPL

Installation

Prerequisites

• Node.js (version 12 or higher)

Setup Instructions

Option 1: Manual Setup

1. Create the project directory structure:

egg-language/
├── src/
├── examples/
└── tests/

2. Copy all the provided files into their respective directories
3. Navigate to the project directory: cd egg-language

Option 2: Using Setup Scripts

On Unix/Linux/macOS:

# Make setup script executable and run it
chmod +x setup.sh
./setup.sh

On Windows:

# Run the Windows setup script
setup.bat

Option 3: Clone from Repository

git clone https://github.com/othaime-en/egg-lang
cd egg-lang
npm install

Usage

Running Programs

All Platforms: Run an Egg program from a file:

# Using npm script
npm start examples/basic.egg

# Using Node directly
node src/egg.js examples/basic.egg

Windows Command Prompt:

node src\egg.js examples\basic.egg

PowerShell (Windows):

node src/egg.js examples/basic.egg

Interactive REPL

Start the interactive shell:

npm run repl
# or
node src/egg.js --repl

Running Tests

Execute the test suite:

npm test

Language Syntax

Basic Values

42          # Numbers
"hello"     # Strings
true        # Boolean true
false       # Boolean false

Variables

define(x, 10)           # Define a variable
set(x, 20)             # Update existing variable

Functions

# Simple function
define(square, fun(x, *(x, x)))
square(5)  # Returns 25

# Multiple parameters
define(add, fun(a, b, +(a, b)))

# Recursive functions
define(factorial, fun(n,
  if(==(n, 0),
     1,
     *(n, factorial(-(n, 1)))
  )
))

Control Flow

# Conditional
if(>(x, 5), print("big"), print("small"))

# Loop
while(<(i, 10),
  do(
    print(i),
    define(i, +(i, 1))
  )
)

# Sequential execution
do(
  define(x, 5),
  define(y, 10),
  +(x, y)
)

Arrays

define(arr, array(1, 2, 3, 4))   # Create array
length(arr)                      # Get length
element(arr, 0)                  # Get element at index

Comments

# This is a comment
define(x, 5)  # Comments can be at end of line
# Multiple lines of comments
# are supported

Built-in Functions

Arithmetic

• +(a, b) - Addition
• -(a, b) - Subtraction
• *(a, b) - Multiplication
• /(a, b) - Division

Comparison

• ==(a, b) - Equality
• !=(a, b) - Inequality
• <(a, b) - Less than
• >(a, b) - Greater than
• <=(a, b) - Less than or equal
• >=(a, b) - Greater than or equal

Logic

• &&(a, b) - Logical AND
• ||(a, b) - Logical OR
• !(a) - Logical NOT

Arrays

• array(...values) - Create array
• length(array) - Get array length
• element(array, index) - Get element at index

Utility

• print(value) - Print value to console
• type(value) - Get type of value

Math

• abs(n) - Absolute value
• min(a, b) - Minimum
• max(a, b) - Maximum
• floor(n) - Floor
• ceil(n) - Ceiling
• round(n) - Round
• random() - Random number 0-1

Examples

Sum of Numbers 1-10

do(
  define(total, 0),
  define(count, 1),
  while(<(count, 11),
    do(
      define(total, +(total, count)),
      define(count, +(count, 1))
    )
  ),
  print(total)  # Prints 55
)

Fibonacci Sequence

do(
  define(fib, fun(n,
    if(<(n, 2),
       n,
       +(fib(-(n, 1)), fib(-(n, 2)))
    )
  )),
  print(fib(10))  # Prints 55
)

Array Processing

do(
  define(numbers, array(5, 2, 8, 1, 9)),
  define(sum, fun(arr,
    do(
      define(i, 0),
      define(total, 0),
      while(<(i, length(arr)),
        do(
          define(total, +(total, element(arr, i))),
          define(i, +(i, 1))
        )
      ),
      total
    )
  )),
  print(sum(numbers))  # Prints 25
)