retoor
5a4054ec66
Add comprehensive demo scripts showcasing the usage of multiple Wren modules including argument parsing, byte manipulation, in-memory dataset operations, HTML encoding/slugification, markdown-to-HTML conversion, UUID generation/validation, schema validation with wdantic, and a full web chat application with REST endpoints.
479 lines
15 KiB
HTML
479 lines
15 KiB
HTML
<!DOCTYPE html>
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<!-- retoor <retoor@molodetz.nl> -->
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<html lang="en">
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<head>
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<meta charset="UTF-8">
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<meta name="viewport" content="width=device-width, initial-scale=1.0">
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<title>Error Handling - Wren-CLI Manual</title>
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<link rel="stylesheet" href="../css/style.css">
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</head>
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<body>
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<button class="mobile-menu-toggle">Menu</button>
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<div class="container">
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<aside class="sidebar">
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<div class="sidebar-header">
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<h1><a href="../index.html">Wren-CLI</a></h1>
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<div class="version">v0.4.0</div>
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</div>
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<nav class="sidebar-nav">
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<div class="section">
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<span class="section-title">Getting Started</span>
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<ul>
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<li><a href="../getting-started/index.html">Overview</a></li>
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<li><a href="../getting-started/installation.html">Installation</a></li>
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<li><a href="../getting-started/first-script.html">First Script</a></li>
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<li><a href="../getting-started/repl.html">Using the REPL</a></li>
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</ul>
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</div>
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<div class="section">
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<span class="section-title">Language</span>
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<ul>
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<li><a href="../language/index.html">Syntax Overview</a></li>
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<li><a href="../language/classes.html">Classes</a></li>
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<li><a href="../language/methods.html">Methods</a></li>
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<li><a href="../language/control-flow.html">Control Flow</a></li>
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<li><a href="../language/fibers.html">Fibers</a></li>
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<li><a href="../language/modules.html">Modules</a></li>
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</ul>
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</div>
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<div class="section">
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<span class="section-title">API Reference</span>
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<ul>
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<li><a href="../api/index.html">Overview</a></li>
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<li><a href="../api/http.html">http</a></li>
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<li><a href="../api/websocket.html">websocket</a></li>
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<li><a href="../api/tls.html">tls</a></li>
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<li><a href="../api/net.html">net</a></li>
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<li><a href="../api/dns.html">dns</a></li>
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<li><a href="../api/json.html">json</a></li>
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<li><a href="../api/base64.html">base64</a></li>
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<li><a href="../api/regex.html">regex</a></li>
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<li><a href="../api/jinja.html">jinja</a></li>
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<li><a href="../api/crypto.html">crypto</a></li>
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<li><a href="../api/os.html">os</a></li>
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<li><a href="../api/env.html">env</a></li>
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<li><a href="../api/signal.html">signal</a></li>
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<li><a href="../api/subprocess.html">subprocess</a></li>
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<li><a href="../api/sqlite.html">sqlite</a></li>
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<li><a href="../api/datetime.html">datetime</a></li>
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<li><a href="../api/timer.html">timer</a></li>
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<li><a href="../api/io.html">io</a></li>
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<li><a href="../api/scheduler.html">scheduler</a></li>
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<li><a href="../api/math.html">math</a></li>
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</ul>
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</div>
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<div class="section">
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<span class="section-title">Tutorials</span>
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<ul>
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<li><a href="../tutorials/index.html">Tutorial List</a></li>
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<li><a href="../tutorials/http-client.html">HTTP Client</a></li>
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<li><a href="../tutorials/websocket-chat.html">WebSocket Chat</a></li>
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<li><a href="../tutorials/database-app.html">Database App</a></li>
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<li><a href="../tutorials/template-rendering.html">Template Rendering</a></li>
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<li><a href="../tutorials/cli-tool.html">CLI Tool</a></li>
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</ul>
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</div>
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<div class="section">
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<span class="section-title">How-To Guides</span>
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<ul>
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<li><a href="index.html">How-To List</a></li>
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<li><a href="http-requests.html">HTTP Requests</a></li>
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<li><a href="json-parsing.html">JSON Parsing</a></li>
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<li><a href="regex-patterns.html">Regex Patterns</a></li>
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<li><a href="file-operations.html">File Operations</a></li>
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<li><a href="async-operations.html">Async Operations</a></li>
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<li><a href="error-handling.html" class="active">Error Handling</a></li>
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</ul>
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</div>
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</nav>
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</aside>
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<main class="content">
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<nav class="breadcrumb">
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<a href="../index.html">Home</a>
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<span class="separator">/</span>
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<a href="index.html">How-To Guides</a>
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<span class="separator">/</span>
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<span>Error Handling</span>
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</nav>
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<article>
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<h1>Error Handling</h1>
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<p>Wren uses fibers for error handling. The <code>fiber.try()</code> method catches errors without crashing your program.</p>
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<h2>Basic Try/Catch Pattern</h2>
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<pre><code>var fiber = Fiber.new {
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Fiber.abort("Something went wrong!")
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}
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var result = fiber.try()
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if (fiber.error) {
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System.print("Error: %(fiber.error)")
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} else {
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System.print("Result: %(result)")
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}</code></pre>
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<h2>Throw an Error</h2>
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<pre><code>Fiber.abort("This is an error message")</code></pre>
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<h2>Catch Specific Error Types</h2>
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<pre><code>var fiber = Fiber.new {
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var x = null
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return x.count // Error: null has no method 'count'
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}
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var result = fiber.try()
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if (fiber.error) {
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if (fiber.error.contains("null")) {
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System.print("Null reference error")
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} else {
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System.print("Other error: %(fiber.error)")
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}
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}</code></pre>
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<h2>Safe File Read</h2>
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<pre><code>import "io" for File
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var safeRead = Fn.new { |path|
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var fiber = Fiber.new { File.read(path) }
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var content = fiber.try()
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if (fiber.error) {
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return null
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}
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return content
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}
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var content = safeRead.call("config.txt")
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if (content) {
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System.print(content)
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} else {
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System.print("Could not read file")
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}</code></pre>
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<h2>Safe JSON Parse</h2>
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<pre><code>import "json" for Json
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var safeParse = Fn.new { |jsonStr|
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var fiber = Fiber.new { Json.parse(jsonStr) }
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var data = fiber.try()
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if (fiber.error) {
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System.print("Invalid JSON: %(fiber.error)")
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return null
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}
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return data
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}
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var data = safeParse.call('{"valid": true}') // Works
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var bad = safeParse.call('not json') // Returns null</code></pre>
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<h2>Safe HTTP Request</h2>
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<pre><code>import "http" for Http
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var safeFetch = Fn.new { |url|
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var fiber = Fiber.new { Http.get(url) }
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var response = fiber.try()
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if (fiber.error) {
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return {"error": fiber.error, "ok": false}
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}
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if (response.statusCode >= 400) {
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return {"error": "HTTP %(response.statusCode)", "ok": false}
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}
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return {"data": response.json, "ok": true}
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}
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var result = safeFetch.call("https://api.example.com/data")
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if (result["ok"]) {
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System.print(result["data"])
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} else {
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System.print("Error: %(result["error"])")
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}</code></pre>
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<h2>Input Validation</h2>
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<pre><code>var validateEmail = Fn.new { |email|
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if (email == null) {
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Fiber.abort("Email is required")
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}
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if (!email.contains("@")) {
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Fiber.abort("Invalid email format")
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}
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return true
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}
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var validate = Fn.new { |email|
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var fiber = Fiber.new { validateEmail.call(email) }
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fiber.try()
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return fiber.error
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}
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System.print(validate.call(null)) // Email is required
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System.print(validate.call("invalid")) // Invalid email format
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System.print(validate.call("a@b.com")) // null (no error)</code></pre>
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<h2>Result Type Pattern</h2>
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<pre><code>class Result {
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construct ok(value) {
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_value = value
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_error = null
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}
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construct error(message) {
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_value = null
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_error = message
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}
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isOk { _error == null }
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isError { _error != null }
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value { _value }
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error { _error }
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unwrap {
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if (isError) Fiber.abort(_error)
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return _value
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}
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unwrapOr(default) { isOk ? _value : default }
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}
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var divide = Fn.new { |a, b|
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if (b == 0) {
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return Result.error("Division by zero")
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}
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return Result.ok(a / b)
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}
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var result = divide.call(10, 2)
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if (result.isOk) {
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System.print("Result: %(result.value)")
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}
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var bad = divide.call(10, 0)
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if (bad.isError) {
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System.print("Error: %(bad.error)")
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}
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System.print(divide.call(10, 5).unwrapOr(0)) // 2
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System.print(divide.call(10, 0).unwrapOr(0)) // 0</code></pre>
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<h2>Assert Function</h2>
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<pre><code>var assert = Fn.new { |condition, message|
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if (!condition) {
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Fiber.abort("Assertion failed: %(message)")
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}
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}
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var processUser = Fn.new { |user|
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assert.call(user != null, "User is required")
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assert.call(user["name"] != null, "User name is required")
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assert.call(user["age"] >= 0, "Age must be non-negative")
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System.print("Processing %(user["name"])...")
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}</code></pre>
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<h2>Multiple Error Sources</h2>
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<pre><code>import "http" for Http
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import "json" for Json
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var fetchAndParse = Fn.new { |url|
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var httpFiber = Fiber.new { Http.get(url) }
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var response = httpFiber.try()
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if (httpFiber.error) {
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return {"error": "Network error: %(httpFiber.error)"}
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}
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if (response.statusCode != 200) {
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return {"error": "HTTP error: %(response.statusCode)"}
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}
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var jsonFiber = Fiber.new { Json.parse(response.body) }
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var data = jsonFiber.try()
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if (jsonFiber.error) {
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return {"error": "Parse error: %(jsonFiber.error)"}
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}
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return {"data": data}
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}
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var result = fetchAndParse.call("https://api.example.com/data")
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if (result.containsKey("error")) {
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System.print(result["error"])
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} else {
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System.print(result["data"])
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}</code></pre>
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<h2>Error Logging</h2>
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<pre><code>import "datetime" for DateTime
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import "io" for File
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class Logger {
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construct new(logFile) {
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_logFile = logFile
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}
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log(level, message) {
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var timestamp = DateTime.now().toString
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var entry = "[%(timestamp)] [%(level)] %(message)\n"
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var existing = ""
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var fiber = Fiber.new { File.read(_logFile) }
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existing = fiber.try() || ""
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File.write(_logFile, existing + entry)
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if (level == "ERROR") {
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System.print("ERROR: %(message)")
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}
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}
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error(message) { log("ERROR", message) }
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warn(message) { log("WARN", message) }
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info(message) { log("INFO", message) }
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}
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var logger = Logger.new("app.log")
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var safeDivide = Fn.new { |a, b|
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if (b == 0) {
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logger.error("Division by zero: %(a) / %(b)")
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return null
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}
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return a / b
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}
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var result = safeDivide.call(10, 0)</code></pre>
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<h2>Cleanup with Finally Pattern</h2>
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<pre><code>import "sqlite" for Sqlite
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var withDatabase = Fn.new { |dbPath, operation|
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var db = Sqlite.open(dbPath)
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var result = null
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var error = null
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var fiber = Fiber.new { operation.call(db) }
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result = fiber.try()
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error = fiber.error
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db.close()
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if (error) {
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Fiber.abort(error)
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}
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return result
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}
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var users = withDatabase.call("app.db", Fn.new { |db|
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return db.execute("SELECT * FROM users")
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})
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System.print(users)</code></pre>
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<h2>Custom Error Class</h2>
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<pre><code>class AppError {
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construct new(code, message) {
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_code = code
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_message = message
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}
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code { _code }
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message { _message }
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toString { "[%(code)] %(message)" }
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static notFound(resource) {
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return AppError.new("NOT_FOUND", "%(resource) not found")
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}
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static validation(field, reason) {
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return AppError.new("VALIDATION", "%(field): %(reason)")
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}
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static unauthorized() {
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return AppError.new("UNAUTHORIZED", "Authentication required")
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}
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}
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var findUser = Fn.new { |id|
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if (id == null) {
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Fiber.abort(AppError.validation("id", "is required").toString)
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}
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var user = null
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if (user == null) {
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Fiber.abort(AppError.notFound("User %(id)").toString)
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}
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return user
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}
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var fiber = Fiber.new { findUser.call(null) }
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fiber.try()
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System.print(fiber.error) // [VALIDATION] id: is required</code></pre>
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<h2>Retry on Error</h2>
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<pre><code>import "timer" for Timer
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var retry = Fn.new { |operation, maxAttempts, delayMs|
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var lastError = null
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for (i in 1..maxAttempts) {
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var fiber = Fiber.new { operation.call() }
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var result = fiber.try()
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if (!fiber.error) {
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return result
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}
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lastError = fiber.error
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System.print("Attempt %(i) failed: %(lastError)")
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if (i < maxAttempts) {
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Timer.sleep(delayMs)
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}
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}
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Fiber.abort("All %(maxAttempts) attempts failed. Last error: %(lastError)")
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}
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var result = retry.call(Fn.new {
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return "success"
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}, 3, 1000)</code></pre>
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<div class="admonition tip">
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<div class="admonition-title">Best Practices</div>
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<ul>
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<li>Always wrap external calls (HTTP, file I/O) in fibers</li>
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<li>Provide meaningful error messages</li>
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<li>Log errors for debugging</li>
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<li>Fail fast on programming errors, recover from user errors</li>
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<li>Clean up resources (close files, connections) even on error</li>
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</ul>
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</div>
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<div class="admonition note">
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<div class="admonition-title">See Also</div>
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<p>For more on fibers, see the <a href="../language/fibers.html">Fibers language guide</a>.</p>
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</div>
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</article>
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<footer class="page-footer">
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<a href="async-operations.html" class="prev">Async Operations</a>
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<a href="../index.html" class="next">Home</a>
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</footer>
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</main>
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<script src="../js/main.js"></script>
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