Lua

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  1. Lua for MediaWiki: A Beginner's Guide

Lua is a powerful, fast, lightweight, embeddable scripting language. While it may sound intimidating, Lua is surprisingly accessible, especially for those looking to extend the functionality of MediaWiki. This article will provide a comprehensive introduction to Lua, specifically geared towards how it’s used within the MediaWiki ecosystem. We'll cover everything from basic syntax to more advanced concepts, and demonstrate how to leverage Lua to create dynamic and powerful wiki extensions and modules.

    1. Why Lua in MediaWiki?

MediaWiki, the software powering Wikipedia and countless other wikis, historically relied primarily on PHP for its core functionality and extensions. However, PHP can sometimes be slow and complex, particularly when dealing with intricate logic. Lua offers several advantages:

  • **Speed:** Lua is significantly faster than PHP in many cases, leading to improved performance for complex operations.
  • **Simplicity:** Lua's syntax is cleaner and easier to learn than PHP.
  • **Embeddability:** Lua is designed to be embedded within other applications, making it a natural fit for MediaWiki.
  • **Security:** Lua’s sandboxing capabilities help mitigate security risks when running user-provided code.
  • **Module System:** Lua's module system allows for better organization and reusability of code.

These benefits have led to the increasing adoption of Lua in MediaWiki, particularly through the use of Modules. Modules allow developers to write Lua code that can be called from wiki templates, offering a flexible and powerful way to extend wiki functionality.

    1. Basic Lua Syntax

Let's start with the fundamentals. Here’s a look at some essential Lua syntax:

      1. Variables

Lua is dynamically typed, meaning you don’t need to declare the type of a variable. Variables are simply assigned values.

```lua myVariable = 10 name = "Lua" isTrue = true ```

      1. Data Types

Lua supports several fundamental data types:

  • **nil:** Represents the absence of a value.
  • **boolean:** `true` or `false`.
  • **number:** Lua numbers are double-precision floating-point numbers by default.
  • **string:** Text enclosed in single or double quotes. `"Hello"` or `'World'`.
  • **table:** The most versatile data structure in Lua. Tables can be used as arrays, dictionaries (associative arrays), or objects.
  • **function:** Code blocks that can be called.
  • **userdata:** Represents data managed by external C libraries.
  • **thread:** Represents an independent thread of execution.
      1. Operators

Lua provides standard arithmetic operators (`+`, `-`, `*`, `/`, `%`), comparison operators (`==`, `~=`, `<`, `>`, `<=`, `>=`), and logical operators (`and`, `or`, `not`).

      1. Control Structures
  • **if-then-else:**

```lua if x > 5 then

 print("x is greater than 5")

else

 print("x is not greater than 5")

end ```

  • **while loop:**

```lua i = 1 while i <= 10 do

 print(i)
 i = i + 1

end ```

  • **for loop (numeric):**

```lua for i = 1, 10 do

 print(i)

end ```

  • **for loop (generic - iterating over tables):**

```lua myTable = {"apple", "banana", "cherry"} for index, value in ipairs(myTable) do

 print(index, value)

end ```

      1. Tables

Tables are central to Lua. Here's how to create and access them:

```lua -- Create a table myTable = {}

-- Add key-value pairs myTable["name"] = "John Doe" myTable[1] = "First Element" myTable.age = 30

-- Access values print(myTable["name"]) -- Output: John Doe print(myTable[1]) -- Output: First Element print(myTable.age) -- Output: 30 ```

      1. Functions

Functions are defined using the `function` keyword:

```lua function greet(name)

 print("Hello, " .. name .. "!")

end

greet("Alice") -- Output: Hello, Alice! ```

    1. Lua Modules in MediaWiki

Modules are the primary way to use Lua within MediaWiki. A module is a Lua script that resides in the wiki's namespace. Modules can be called from wiki templates using the `#invoke` parser function.

      1. Creating a Module

1. **Create a page:** Create a new page in the `Module:` namespace (e.g., `Module:MyModule`). 2. **Add Lua code:** Add your Lua code to the page. The code *must* be enclosed within `return` statements. This is because the `#invoke` function expects the module to return a table containing the functions you want to call.

```lua -- Module:MyModule local module = {}

function module.square(x)

 return x * x

end

function module.concatenate(str1, str2)

 return str1 .. str2

end

return module ```

      1. Calling a Module from a Template

1. **Create a Template:** Create a new template (e.g., `Template:MyTemplate`). 2. **Use `#invoke`:** Use the `#invoke` parser function to call the module:

```wiki {{#invoke:MyModule|square|5}} {{#invoke:MyModule|concatenate|Hello| World}} ```

This will output:

  • 25
  • Hello World
      1. Module Parameters

You can pass parameters to module functions:

```lua -- Module:MyModule local module = {}

function module.greet(name)

 return "Hello, " .. name .. "!"

end

return module ```

```wiki {{#invoke:MyModule|greet|Alice}} -- Outputs: Hello, Alice! ```

    1. Advanced Lua Concepts for MediaWiki
      1. Metatables and Metamethods

Metatables allow you to define custom behavior for tables. Metamethods are special functions that are called when certain operations are performed on a table. This is useful for creating custom data types and controlling how tables interact with each other. This is often used in creating more complex data structures for technical analysis.

      1. Local Variables

Using the `local` keyword declares a variable with local scope, meaning it's only accessible within the block of code where it's defined. This helps prevent naming conflicts and improves code organization. Always use `local` unless you specifically need a global variable.

      1. Error Handling

Lua provides error handling mechanisms using `pcall`. `pcall` allows you to call a function in a protected mode, catching any errors that occur.

```lua local status, result = pcall(function()

 -- Code that might cause an error
 return 10 / 0 -- Division by zero

end)

if not status then

 print("Error: " .. result)

end ```

      1. Debugging

Lua’s debugging tools are relatively simple, but effective. The `print` function is your primary debugging tool. You can also use a debugger if you’re developing locally. Understanding the error messages is crucial for identifying and fixing problems. Often, errors relate to incorrect table indexing or misunderstood function parameters. Debugging is essential for creating robust trading strategies.

      1. Utilizing Libraries

Lua boasts a rich ecosystem of libraries. While directly incorporating external C libraries into MediaWiki modules can be complex, several useful Lua libraries are already available or can be adapted for use. These can be incredibly helpful for tasks like data manipulation, string processing, and mathematical calculations often used in market trend analysis.

    1. Best Practices for Lua in MediaWiki
  • **Use `local` variables:** Always use `local` to scope your variables.
  • **Comment your code:** Clearly comment your code to explain its purpose and functionality.
  • **Keep modules small and focused:** Each module should have a specific purpose.
  • **Test thoroughly:** Test your modules and templates thoroughly to ensure they work as expected.
  • **Follow the MediaWiki coding style:** Adhere to the MediaWiki coding style guidelines for consistency.
  • **Consider Performance:** Lua is fast, but inefficient code can still slow things down. Optimize your code for performance, especially for frequently used modules. Understanding candlestick patterns and implementing them efficiently requires careful coding.
  • **Security First:** When dealing with user input, sanitize and validate it carefully to prevent security vulnerabilities.
  • **Error Handling:** Implement robust error handling to gracefully handle unexpected situations.
  • **Documentation:** Document your modules and templates clearly so that others can understand and use them. This is especially important for complex indicators and algorithms.
    1. Resources for Learning More
    1. Conclusion

Lua is a valuable tool for extending the functionality of MediaWiki. By understanding the basics of Lua syntax and the principles of module development, you can create powerful and dynamic wiki extensions. The resources provided will help you continue your learning journey and unlock the full potential of Lua within the MediaWiki environment. Remember to practice, experiment, and consult the documentation to become proficient in this versatile scripting language.

Help:Lua Extension:Scribunto Manual:Modules Template:Invoke MediaWiki PHP Debugging Variables Data Types Tables Functions

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