Parser Functions
- Parser Functions
Parser functions are a powerful and versatile tool within MediaWiki that allow you to perform calculations, manipulate strings, and control the display of content dynamically within wiki pages. They are essentially built-in functions that are processed by the wiki parser *before* the page is rendered, allowing for complex logic and content generation without requiring any programming knowledge beyond the syntax of the functions themselves. This article provides a comprehensive introduction to parser functions, aimed at beginners, covering their basic syntax, common functions, and practical examples. Understanding these functions will significantly enhance your ability to create dynamic and informative wiki pages.
== What are Parser Functions?
At their core, parser functions are snippets of code that are interpreted by the MediaWiki software as it processes a wiki page. Unlike other wiki markup, which is primarily for *formatting* content, parser functions are for *processing* content. They take input, perform an operation, and return a result, which is then displayed on the page. This result can be text, a number, a boolean value (true/false), or even a category assignment.
Think of them as a mini-programming language embedded within the wiki syntax. While not as powerful as a full-fledged programming language like Python or JavaScript, they are remarkably effective for a wide range of tasks. They are particularly useful for:
- **Dynamic Content:** Displaying information that changes based on input or variables.
- **Calculations:** Performing mathematical operations directly within the wiki page.
- **String Manipulation:** Extracting, replacing, and formatting text.
- **Conditional Logic:** Showing or hiding content based on certain conditions.
- **Data Organization:** Creating tables and lists with data generated by the functions.
- **Template Enhancement:** Making templates more flexible and reusable. Templates are a key element in utilizing Parser Functions effectively.
== Basic Syntax
All parser functions begin with the `#` character. This signals to the parser that the following text is a function call and should be interpreted accordingly. The general syntax is:
`{{#function: input1 | input2 | ... | format }}`
Let's break this down:
- `Template:...`: This double curly brace notation is used to enclose the function call. It's similar to how you would use variables or templates.
- `#function`: This is the name of the parser function you want to use (e.g., `#if`, `#expr`, `#title`).
- `input1 | input2 | ...`: These are the arguments or inputs that the function requires. Arguments are separated by the vertical bar `|` character. The number and type of inputs vary depending on the function.
- `format` (optional): Some functions accept an optional format argument to control the output.
- Important Considerations:**
- **Case Sensitivity:** Parser function names are *not* case-sensitive. `#IF` is the same as `#if`.
- **Whitespace:** Whitespace around the `|` character is generally ignored, but it's good practice to keep it consistent for readability.
- **Nested Functions:** You can nest parser functions within each other to create more complex logic. However, be mindful of readability and potential performance issues with deeply nested structures.
- **Recursion:** Parser functions do *not* support recursion (a function calling itself).
- **Performance:** Overuse of complex parser functions can slow down page rendering, especially on heavily used pages. Consider alternative approaches if performance becomes a concern. Help:Performance offers guidance on optimizing wiki pages.
== Common Parser Functions
Here’s a detailed look at some of the most commonly used parser functions:
- 1. `#if` (Conditional Statement)**
The `#if` function checks if an expression evaluates to a non-empty string. If it does, it displays the first argument; otherwise, it displays the second argument (or nothing if only one argument is provided).
`{{#if: expression | then | else}}`
- `expression`: The condition to evaluate.
- `then`: The content to display if the expression is true.
- `else`: The content to display if the expression is false (optional).
- Example:**
`{{#if: 1 | This is true | This is false}}` Displays: "This is true"
`{{#if: | This is true | This is false}}` Displays: "This is false"
- 2. `#ifeq` (Equality Check)**
The `#ifeq` function checks if two strings are equal.
`{{#ifeq: string1 | string2 | then | else}}`
- `string1`: The first string to compare.
- `string2`: The second string to compare.
- `then`: The content to display if the strings are equal.
- `else`: The content to display if the strings are not equal (optional).
- Example:**
`{{#ifeq: apple | apple | The fruits are the same | The fruits are different}}` Displays: "The fruits are the same"
`{{#ifeq: apple | orange | The fruits are the same | The fruits are different}}` Displays: "The fruits are different"
- 3. `#switch` (Multiple Conditions)**
The `#switch` function allows you to check a string against multiple possible values. It's like a more powerful version of `#if` with multiple conditions.
`{{#switch: string | case1 | result1 | case2 | result2 | ... | default}}`
- `string`: The string to evaluate.
- `case1 | result1`: A case-result pair. If `string` matches `case1`, `result1` is displayed.
- `default`: The content to display if `string` doesn't match any of the cases (optional).
- Example:**
`{{#switch: color | red | The color is red | blue | The color is blue | green | The color is green | The color is unknown}}`
- 4. `#expr` (Mathematical Expression)**
The `#expr` function evaluates a mathematical expression. It supports basic arithmetic operations (+, -, *, /, %), as well as some functions like `sqrt()` (square root) and `pow()` (power).
`{{#expr: expression}}`
- `expression`: The mathematical expression to evaluate.
- Example:**
`{{#expr: 2 + 3 * 4}}` Displays: "14"
`{{#expr: sqrt(16)}}` Displays: "4"
This function is invaluable for calculating values within wiki pages, for example, in Technical Analysis contexts like calculating moving averages or Relative Strength Index (RSI). Understanding Candlestick Patterns often requires quick calculations, which `#expr` facilitates.
- 5. `#title` (Page Title)**
The `#title` function returns the title of a page, optionally formatted.
`{{#title: page title | format}}`
- `page title`: The title of the page to retrieve.
- `format`: An optional format argument:
* `unencoded`: Returns the title without any URL encoding. * `escaped`: Returns the title with wiki markup escaped.
- Example:**
`{{#title: Main Page}}` Displays: "Main Page"
- 6. `#category` (Category Assignment)**
The `#category` function assigns a page to a category. This is a simple way to categorize pages dynamically.
`{{#category: Category Name}}`
- `Category Name`: The name of the category to assign the page to.
- Example:**
`{{#category:Parser Functions Documentation}}`
- 7. `#property` (Property Retrieval)**
The `#property` function retrieves a property associated with a page. This requires the use of Semantic Wiki extensions.
`{{#property: page title | property name}}`
- `page title`: The title of the page to retrieve the property from.
- `property name`: The name of the property to retrieve.
- 8. `#time` (Date and Time Formatting)**
The `#time` function formats a date and time value. It's useful for displaying timestamps or calculating time differences. Requires careful understanding of the format codes.
`{{#time: format | timestamp}}`
- `format`: The format string (e.g., `Y`, `m`, `d`, `H`, `i`, `s`). Refer to PHP date/time format documentation for available codes.
- `timestamp`: The timestamp to format. If omitted, it uses the current time.
- Example:**
`{{#time: Y-m-d H:i:s}}` Displays the current date and time in the format "YYYY-MM-DD HH:MM:SS".
- 9. `#vardefine` and `#varbykey` (Variable Definition and Access)**
These functions, introduced in more recent MediaWiki versions (1.34+), allow you to define and access variables within a page. This is crucial for more complex logic and data management.
- `#vardefine: name | value`: Defines a variable named `name` with the value `value`.
- `#varbykey: key | default`: Retrieves the value associated with the key `key`. If the key is not found, it returns the `default` value.
These functions are extremely useful for creating reusable components and managing data within a wiki page, particularly in the context of Trading Strategies where parameters need to be defined and accessed repeatedly.
- 10. `#arraymap` (Array Manipulation)**
This function applies a function to each element of an array. It's a powerful tool for processing lists of data. Requires a good understanding of array syntax within MediaWiki.
`{{#arraymap: function | array}}`
- `function`: The function to apply to each element.
- `array`: The array of elements.
== Practical Examples and Advanced Techniques
Let's explore some more advanced examples that demonstrate the power of parser functions:
- **Calculating Profit/Loss:** Using `#expr` to calculate the profit or loss of a trade based on entry and exit prices. This is directly applicable to Risk Management and Position Sizing.
- **Creating Dynamic Tables:** Combining `#if` and `#switch` to generate tables with content that changes based on input parameters. This is useful for displaying Market Data or Economic Calendars.
- **Conditional Formatting:** Using `#if` to apply different formatting to content based on certain conditions, such as highlighting positive or negative values. This is helpful in visualising Trend Analysis.
- **Implementing Basic Logic:** Combining multiple functions to create more complex logic, such as checking if a trade meets certain criteria before displaying it. This is essential for automated Trading Systems.
- **Creating Custom Indicators:** While not a replacement for dedicated extensions, `#expr` can be used to implement simple Technical Indicators like Moving Averages or MACD.
- **Dynamic Category Assignment:** Using `#if` or `#switch` to assign a page to different categories based on its content. This helps with efficient Wiki Organization.
- **String Manipulation for Data Extraction:** Utilizing string functions (often in combination with `#expr`) to extract specific data points from larger strings. This is useful for parsing data from external sources.
== Limitations and Best Practices
While powerful, parser functions have limitations:
- **Complexity:** Complex logic can become difficult to read and maintain.
- **Performance:** Overuse can slow down page rendering.
- **Debugging:** Debugging can be challenging due to the lack of a dedicated debugger.
- **Security:** Be cautious when using user-supplied input in parser functions, as it could potentially lead to security vulnerabilities.
- Best Practices:**
- **Keep it Simple:** Break down complex logic into smaller, more manageable functions.
- **Use Comments:** Add comments to explain your code.
- **Test Thoroughly:** Test your functions with various inputs to ensure they work as expected.
- **Consider Alternatives:** If performance is critical, consider using extensions or server-side scripting instead of parser functions.
- **Document Your Code:** Explain what each function does and how to use it.
By understanding these limitations and following best practices, you can effectively leverage parser functions to create dynamic and informative wiki pages. Remember to consult the Help:ParserFunctions page for the most up-to-date documentation and examples. Further exploration of MediaWiki Extensions can unlock even greater functionality. Understanding Wiki Markup is also crucial for integrating Parser Function results into a well-formatted page. Finally, consider studying Lua scripting within MediaWiki for more advanced automation possibilities.
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