Tutorials

variablesstringintegernumberbooleantoString

Variables and Types

Store values in variables and discover Clean's four basic types.

string interpolationtrimtoUpperCasecontainsreplacechaining

Working with Text

Use string interpolation and the most common string operations.

Making Decisions

Use if, else if, and else to run different code based on conditions.

ifelseelse ifandornot

iteratewhilerangebreakcontinue

Loops: Doing Things More Than Once

Use iterate and while loops to repeat code, and break or continue to control the flow.

listaddlengthindex accesscontainsiterate

Lists: Keeping Groups of Things

Create and work with lists of values — add, access, iterate, and check.

functions blockparametersreturnvoid

Writing Your Own Functions

Write reusable functions with parameters and return values.

beginner7 min

Classes: Grouping Data and Behavior

Define classes with fields, constructors, and methods — then build on them with inheritance.

classconstructorfieldsmethodsinheritancebase

erroronErrorfallbackerror handling

Handling Errors

Raise errors with error() and catch them gracefully with onError.

MCP serverAIrequirecontractscln mcp-server

Your AI Coding Partner

Use the MCP server to get AI assistance that knows the exact Clean Language spec.

Build a Web App

frame.serverendpoints server:http.respond

Your First Web Server

Create a server with endpoints that respond to HTTP requests. You'll have something running in under 5 minutes.

html: blockfunctions:raw interpolationpage structure

Returning HTML Pages

Serve complete HTML pages from your server. Use helper functions to keep your page structure consistent across every route.

req.param:param syntaxdynamic routes

Route Parameters

Read values from the URL path and use them to serve dynamic content. One endpoint handles /users/alice, /users/bob, and every name in between.

beginner8 min

Reading from a Database

Connect to MySQL and query your data. Display database records in a web page using db.query and json.get.

frame.datadb.queryjson.getSQL params

intermediate8 min

Saving Data to a Database

Handle POST requests and save form data to your database. Build the write side of your web application.

POST endpointsreq.bodyINSERTvalidation

intermediate5 min

Building Reusable Components

Create functions that return HTML — Clean Language's component model. Write a card, a button, or a nav bar once and use it everywhere.

functions:html: blockreusable componentsraw interpolation

intermediate8 min

Listing Records from a Database

Fetch multiple rows and render them as a list. This pattern powers every feed, search result, and dashboard in your app.

COUNT queryiteratejson.get with indexlisting pattern

req.queryfilteringconditional SQLsearch

Query Parameters and Search

Read URL query strings to filter results. Add search and filtering to any listing page without changing your routes.

application/jsonAPI designerror responseshealth check

JSON API Endpoints

Return JSON instead of HTML. Build API endpoints that mobile apps, frontend JavaScript, or other services can consume.

intermediate10 min

Putting It All Together

Build a complete bookmarks app — add URLs, list them, view them. Every pattern from this track working together in one real project.

full-stack appCRUDcomponentsmultiple routes

Language in Depth

stringintegernumberbooleantype conversion

Types and Conversions

Understand Clean Language's four core types and how to convert between them. The type system catches mistakes before they reach production.

return typesfunction compositiontyped parametersboolean functions

Functions in Depth

Write functions that call each other, return different types for different conditions, and build complex behavior from simple pieces.

list.add()index access.contains().length()iterate

List Operations

Everything you can do with a list — add items, access by index, check membership, iterate, and build new lists from existing ones.

.trim().toUpperCase().contains().replace().split().slice()

The String Toolkit

A practical guide to Clean Language's string methods — the ones that appear in real programs, with examples that show when to reach for each one.

classconstructorpropertiesmethodsinstances

Designing Classes

Bundle data and behavior into a class. Write a constructor, define methods, and create multiple independent instances from the same template.

isbase()inheritancemethod overrideparent class

Class Inheritance

Extend a class with is and call the parent constructor with base(). Reuse behavior from a parent and add or override what the child needs.

intermediate5 min

Contracts with require

State function preconditions explicitly. require is documentation and enforcement in one line — the compiler and runtime guarantee the contract is honored.

requirepreconditionscontractsdefensive programming

error()onErrorerror propagationdefensive programming

Error Handling in Depth

Signal errors with error() and handle them at the call site with onError. Make error handling explicit, local, and readable.