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Build your own Interpreter

Learn about tokenization, ASTs, tree-walk interpreters and more.

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This challenge is free to try when it's in beta. We keep challenges in beta for a few weeks to gather feedback.

This challenge follows the book Crafting Interpreters by Robert Nystrom.

In this challenge you'll build an interpreter for Lox, a simple scripting language. Along the way, you'll learn about tokenization, ASTs, tree-walk interpreters and more.

Before starting this challenge, make sure you've read the "Welcome" part of the book that contains these chapters:

These chapters don't involve writing code, so they won't be covered in this challenge. This challenge will start from chapter 4, Scanning.

Stages

Scanning: Empty file
Scanning: Parentheses
Scanning: Braces
Scanning: Other single-character tokens
Scanning: Lexical errors
Scanning: Assignment & equality Operators
Scanning: Negation & inequality operators
Scanning: Relational operators
Scanning: Division operator & comments
Scanning: Whitespace
Scanning: Multi-line errors
Scanning: String literals
Scanning: Number literals
Scanning: Identifiers
Scanning: Reserved words

Parsing Expressions

Booleans & Nil
Number literals
String literals
Parentheses
Unary Operators
Arithmetic operators (1/2)
Arithmetic operators (2/2)
Comparison operators
Equality operators
Syntactic errors

Evaluating Expressions

Literals: Booleans & Nil
Literals: Strings & Numbers
Parentheses
Unary Operators: Negation & Not
Arithmetic Operators (1/2)
Arithmetic Operators (2/2)
String Concatenation
Relational Operators
Equality Operators
Runtime Errors: Unary Operators
Runtime Errors: Binary Operators (1/2)
Runtime Errors: Binary Operators (2/2)
Runtime Errors: Relational Operators

Statements & State

Print: Generate output
Print: Multiple statements
Expression statements
Variables: Declare variables
Variables: Runtime Errors
Variables: Initialize variables
Variables: Redeclare variables
Assignment operation
Block syntax
Scopes

Control Flow

If statements
Else statements
Else-if statements
Nested if statements
Logical OR operator
Logical AND operator
While statements
For statements
Syntactic errors

Functions

Native functions
Functions without arguments
Functions with arguments
Syntax errors
Return statements
Higher order functions
Runtime errors
Function scope
Closures

Resolving & Binding

Identifier Resolution
Self Initialization
Variable Redeclaration
Invalid Return

Classes

Class Declarations
Class Instances
Getters & Setters
Instance Methods
The 'this' keyword
Invalid usages of 'this'
Constructor calls
Return within constructors
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