Help:ParserFunctions

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  1. Help:ParserFunctions

ParserFunctions are a powerful set of functions within MediaWiki that allow you to perform calculations, string manipulation, and conditional logic directly within wiki text. They significantly extend the capabilities of wiki pages beyond simple formatting and linking, enabling dynamic content generation and more complex page structures. This guide will provide a comprehensive introduction to ParserFunctions, aimed at beginners, covering their syntax, common functions, and practical examples.

What are ParserFunctions?

At their core, ParserFunctions are snippets of code that are evaluated by the MediaWiki parser when a page is rendered. They are enclosed in double curly braces `Template:...`. Unlike templates, which are essentially pre-defined chunks of wiki text, ParserFunctions operate on data *within* the wiki text at the time of page view. This means the output of a ParserFunction can change based on variables, conditions, and the content surrounding the function call.

Think of them as a simple scripting language embedded within Wiki markup. While not as powerful as full programming languages like Python or PHP, they offer a substantial amount of flexibility for creating dynamic and interactive wiki content. They are particularly useful for:

  • Calculating values (e.g., totals, averages)
  • Formatting dates and times
  • Conditional display of content (e.g., showing different text based on user group)
  • String manipulation (e.g., extracting parts of a string, replacing text)
  • Creating simple tables and lists based on data

Basic Syntax

The general syntax for using a ParserFunction is as follows:

`Template:ParserFunctionName: parameter1`

  • `ParserFunctionName`: The name of the function you want to use (e.g., `#if`, `#expr`, `#time`).
  • `parameter1`, `parameter2`, ...: The input values the function operates on. Parameters are separated by the pipe symbol `|`.
  • The pipe symbol also acts as a separator between arguments.

It's important to note the following:

  • ParserFunction names are always preceded by a hash symbol `#`.
  • Whitespace within the curly braces is generally ignored.
  • Most functions accept a variable number of parameters.
  • The specific parameters accepted by each function are described in the documentation for that function (see Help:Magic words).
  • ParserFunctions are case-sensitive. `#if` is different from `#IF`.

Common ParserFunctions

Here's a breakdown of some of the most frequently used ParserFunctions. We’ll cover each with examples.

#if: Conditional Logic

The `#if` function allows you to display content only if a certain condition is true.

Syntax: `{{#if: condition | then | else}}`

  • `condition`: An expression that evaluates to true or false. Common conditions include:
   *   Checking if a variable is empty:  `{{#if:
  1. Template:Var – A Beginner's Guide

Template:Var is a fundamental, yet often overlooked, tool in the MediaWiki ecosystem. It provides a mechanism for defining and reusing variables within templates, drastically improving code readability, maintainability, and flexibility. This article aims to provide a comprehensive guide to `Template:Var`, geared towards beginners, covering its basic usage, advanced techniques, common pitfalls, and best practices. Understanding `Template:Var` is crucial for anyone looking to create complex and reusable templates on a MediaWiki platform. We will also explore how it relates to other template features and its potential applications.

What is Template:Var?

At its core, `Template:Var` allows you to define named parameters within a template that can be accessed and reused multiple times within the template's code. Without `Template:Var`, you would need to repeat the same value or expression throughout your template whenever you needed it, leading to verbose and error-prone code. `Template:Var` promotes the "DRY" (Don't Repeat Yourself) principle, making templates easier to understand, modify, and debug.

Imagine you're creating a template to display a stock chart. You might need the stock ticker symbol, the chart time frame (e.g., daily, weekly), and the chart type (e.g., candlestick, line) repeatedly throughout the template to generate different chart elements. Instead of typing these values multiple times, you can define them as variables using `Template:Var` and then reference those variables wherever needed.

Basic Usage

The syntax for defining a variable using `Template:Var` is as follows:

```wiki {{#var:variable_name | value}} ```

  • `#var`: This is the parser function that initiates the variable definition.
  • `variable_name`: This is the name you choose for your variable. It should be descriptive and follow MediaWiki's naming conventions (avoid spaces and special characters).
  • `value`: This is the value you want to assign to the variable. It can be a literal string, a number, another template call, or even a more complex expression.

To access the variable's value later in the template, you use the following syntax:

```wiki {{{variable_name}}} ```

Here’s a simple example:

```wiki {{#var:stock_ticker | AAPL}} Stock Ticker: {{{stock_ticker}}} ```

This would output:

``` Stock Ticker: AAPL ```

Example: A Simple Stock Information Template

Let’s create a more practical example. Suppose we want to create a template that displays basic information about a stock.

```wiki

{{#var:stock_name | Default Stock Name}} {{#var:stock_ticker | Default Ticker}} {{#var:current_price | 0.00}}

Stock Name: {{{stock_name}}} Stock Ticker: {{{stock_ticker}}} Current Price: {{{current_price}}}

Technical Analysis Notes:

Trading Strategies:

```

Now, we can use this template like this:

```wiki Template:StockInfo ```

This would output:

``` Stock Name: Apple Inc. Stock Ticker: AAPL Current Price: 170.34

Technical Analysis Notes:

Trading Strategies:

```

Notice how we've overridden the default values defined in the template with specific values when calling it. If we omit a parameter when calling the template, the default value will be used.

Advanced Techniques

  • **Default Values:** As seen in the example above, `Template:Var` automatically provides default values. This makes templates more robust and easier to use.
  • **Conditional Logic:** You can combine `Template:Var` with parser functions like `{{#if}}` or `{{#switch}}` to create conditional logic within your templates.
   ```wiki
   {{#var:show_analysis | false}}

   {{#if:{{{show_analysis}}}
     | Detailed Analysis:
     |  (Analysis hidden)
   }}
   ```
  • **Template Calls within Variables:** You can assign the result of another template call to a variable. This allows you to build complex templates by composing smaller, reusable components.
   ```wiki
   {{#var:formatted_price | {{FormatPrice:{{{current_price}}}}} }}
   Formatted Price: {{{formatted_price}}}
   ```
  • **Looping with Template:Loop:** While more complex, `Template:Var` can be used in conjunction with `Template:Loop` to iterate over a list of items and generate dynamic content. This is particularly useful for creating tables or lists based on data stored in a variable. See also Help:Loop.
  • **Variable Scope:** Variables defined within a template are local to that template. They are not accessible from outside the template unless explicitly returned as part of the template's output.
  • **Using Variables in other Parser Functions:** `Template:Var` variables can seamlessly integrate with other parser functions such as `{{#time}}`, `{{#titlecase}}`, and `{{#formatnum}}`. This expands functionality significantly.
  • **Combining with Template:Args:** For more complex parameter handling, consider using `Template:Var` alongside `Template:Args`. `Template:Args` is useful for processing a variable number of arguments. See also Help:Args.

Common Pitfalls and How to Avoid Them

  • **Incorrect Variable Names:** Double-check that you're using the correct variable names when accessing them. Case sensitivity matters. Typos are a common source of errors.
  • **Missing Default Values:** If you don't provide a default value and the parameter is not specified when calling the template, the variable will be empty, which might lead to unexpected results. Always consider providing sensible defaults.
  • **Circular Dependencies:** Avoid creating circular dependencies between templates, where template A relies on template B, and template B relies on template A. This can lead to infinite loops and errors.
  • **Overuse of Variables:** While `Template:Var` is powerful, don't overuse it. For very simple templates with only a few parameters, it might be overkill. Strive for a balance between readability and conciseness.
  • **Security Concerns:** Be cautious when using user-supplied input directly in variables, especially if the input is used in other parser functions or template calls. Consider using sanitization techniques to prevent potential security vulnerabilities. This is particularly important if dealing with data from external sources.
  • **Conflicting Variable Names:** Ensure that variable names are unique within a template to avoid conflicts and unexpected behavior.

Best Practices

  • **Use Descriptive Variable Names:** Choose variable names that clearly indicate the purpose of the variable. This makes your templates easier to understand and maintain.
  • **Provide Meaningful Default Values:** Default values should be sensible and prevent errors when a parameter is not specified.
  • **Document Your Templates:** Clearly document the purpose of each variable and any special considerations. Use the `` tags to include documentation.
  • **Test Thoroughly:** Test your templates with various inputs to ensure they behave as expected.
  • **Keep Templates Modular:** Break down complex templates into smaller, reusable components to improve maintainability.
  • **Use Consistent Formatting:** Follow a consistent formatting style for your template code to improve readability.
  • **Consider Template Categories:** Place your templates into appropriate categories to make them easier to find and reuse.

Relationship to Other Template Features

`Template:Var` complements other MediaWiki template features such as:

  • **Parameters:** `Template:Var` is used to define and manage parameters passed to a template.
  • **Parser Functions:** `Template:Var` can be used in conjunction with parser functions to perform calculations, manipulate strings, and add conditional logic.
  • **Template Includes:** You can use `Template:Var` to pass variables to included templates.
  • **Modules:** For more complex logic, consider using Module:Sandbox to create reusable functions that can be called from templates, using variables passed via `Template:Var`.
  • **TemplateData:** Allows for structured documentation of template parameters, aiding editors in using the template correctly.

Advanced Considerations for Financial Data Templates

When building templates dealing with financial data (like the stock information template example), consider the following:

  • **Data Sources:** Where is the data coming from? Consider using reliable APIs for real-time data.
  • **Data Formatting:** Use `{{#formatnum}}` to format numbers with appropriate separators and decimal places.
  • **Currency Symbols:** Handle currency symbols correctly using appropriate formatting.
  • **Volatility Indicators:** Integrate indicators like Bollinger Bands or Average True Range to assess volatility.
  • **Trend Identification:** Implement tools for identifying trends, such as MACD or Ichimoku Cloud.
  • **Chart Integration:** Explore ways to integrate chart libraries into your templates (this may require extensions or JavaScript).
  • **Risk Management:** Include disclaimers and warnings about the risks of trading.
  • **Market Sentiment Analysis:** Consider incorporating sentiment indicators based on news and social media data.
  • **Economic Calendars:** Provide links to economic calendars to help users stay informed about important events.
  • **Correlation Analysis:** Explore the correlation between different assets.
  • **Options Pricing Models:** For options trading templates, consider incorporating options pricing models like Black-Scholes.
  • **Candlestick Pattern Recognition:** Implement logic to identify common candlestick patterns like Doji, Hammer, and Engulfing Patterns.
  • **Volume Analysis:** Analyze trading volume to confirm trends and identify potential reversals.
  • **Support and Resistance Levels:** Dynamically identify support and resistance levels based on price action.
  • **Elliott Wave Theory:** (Advanced) Consider incorporating elements of Elliott Wave Theory.
  • **Gann Analysis:** (Advanced) Explore Gann analysis techniques.
  • **Fundamental Analysis:** Link to resources for fundamental analysis of companies.
  • **News Integration:** Display relevant news headlines related to the stock.
  • **Earnings Reports:** Provide links to earnings reports and financial statements.
  • **Analyst Ratings:** Display analyst ratings and price targets.
  • **Short Interest Ratio:** Show the short interest ratio.



Help:Templates Help:Variables Help:ParserFunctions Help:Args Help:Loop Module:Sandbox Template:Documentation Help:Categories Moving Averages Relative Strength Index Fibonacci Retracements Day Trading Swing Trading Scalping Black-Scholes Bollinger Bands Average True Range MACD Ichimoku Cloud Doji Hammer Engulfing Patterns

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   *   Comparing strings: `{{#if: Template:String1 = Template:String2 | Strings are equal | Strings are different}}`
   *   Checking if a page exists: `{{#ifexist: Page Name | Page exists | Page does not exist}}`
  • `then`: The content to display if the condition is true.
  • `else`: (Optional) The content to display if the condition is false. If omitted, nothing is displayed.

Example:

`{{#if: 1+1=2 | This is true! | This is false!}}` will display "This is true!".

#expr: Mathematical Expressions

The `#expr` function evaluates mathematical expressions.

Syntax: `{{#expr: expression}}`

  • `expression`: A mathematical expression using standard operators (+, -, *, /, %, ^ (exponentiation)).

Example:

`{{#expr: 2 + 3 * 4}}` will display "14".

You can use variables within `#expr`:

`{{#expr: Template:Value1 + Template:Value2}}`

This allows you to perform calculations based on values defined elsewhere in the wiki. This is useful for calculating Moving Averages, Relative Strength Index (RSI), and other Technical Indicators.

#time: Date and Time Formatting

The `#time` function formats dates and times.

Syntax: `{{#time: format | timestamp}}`

  • `format`: A string specifying the desired date and time format. See the Help:Formatting dates and times page for a complete list of format codes.
  • `timestamp`: (Optional) A timestamp representing the date and time to format. If omitted, the current time is used. Timestamps can be represented as numbers (seconds since the Unix epoch) or as strings in a recognized date/time format.

Example:

`{{#time: Y-m-d}}` will display the current date in the format "YYYY-MM-DD".

`{{#time: H:i:s}}` will display the current time in the format "HH:MM:SS".

`{{#time: d F Y | 1678886400}}` will display "15 March 2023" (formatted from a Unix timestamp).

#switch: Multiple Conditions

The `#switch` function allows you to choose between multiple options based on a given value.

Syntax: `{{#switch: value | case1 = result1 | case2 = result2 | ... | default = defaultResult}}`

  • `value`: The value to compare against the cases.
  • `case1 = result1`, `case2 = result2`, ...: Pairs of case values and corresponding results.
  • `default = defaultResult`: (Optional) The result to display if none of the cases match.

Example:

`{{#switch: Template:Fruit | apple = red | banana = yellow | orange = orange | default = unknown}}`

If the variable `fruit` is set to "apple", the output will be "red". If it’s set to "banana", the output will be "yellow", and so on. If `fruit` is set to any other value, the output will be "unknown". This is useful for categorizing Trading Strategies based on their risk level.

#var: Variable Assignment

The `#var` function allows you to assign a value to a variable. Variables defined with `#var` are available for use in other ParserFunctions within the same page.

Syntax: `{{#var: variableName | value}}`

  • `variableName`: The name of the variable to create or update.
  • `value`: The value to assign to the variable.

Example:

`{{#var: price | 100}}` `The current price is: Template:Price`

This will display "The current price is: 100". Variables are particularly helpful when calculating Fibonacci retracements or implementing complex Elliott Wave analyses.

#title: Extracting Page Title Information

The `#title` function allows you to extract information from a page title.

Syntax: `{{#title: pageName | part}}`

  • `pageName`: The name of the page to extract information from.
  • `part`: Specifies which part of the title to extract. Possible values include:
   *   `part=1`: The first word of the title.
   *   `part=2`: The second word of the title, and so on.
   *   `part=-1`: The last word of the title.
   *   `part=-2`: The second to last word of the title, and so on.

Example:

If the page title is "Technical Analysis of Stocks", then:

`{{#title: Technical Analysis of Stocks | part=1}}` will display "Technical". `{{#title: Technical Analysis of Stocks | part=-1}}` will display "Stocks".

#category: Adding Categories

While the category is typically added directly using brackets ``, the `#category` function can be used within ParserFunctions to dynamically add categories. This is less common but can be useful in certain scenarios.

Syntax: `{{#category: Category Name}}`

Example:

`{{#if: Template:RiskLevel = high | {{#category: High Risk Strategies}} | {{#category: Low Risk Strategies}} }}`

This will add the page to either the "High Risk Strategies" or "Low Risk Strategies" category based on the value of the `riskLevel` variable.

#random: Generating Random Numbers

The `#random` function generates a random number.

Syntax: `{{#random: from | to}}`

  • `from`: The minimum value (inclusive). Defaults to 1.
  • `to`: The maximum value (inclusive). Defaults to 100.

Example:

`{{#random: 1 | 10}}` will generate a random integer between 1 and 10. This could be used to simulate Monte Carlo simulations for risk assessment.

#formattime: More Flexible Time Formatting

The `#formattime` function provides more granular control over date and time formatting than `#time`. It's particularly useful for handling time differences and relative dates.

Syntax: `{{#formattime: format | time}}`

  • `format`: A format string similar to PHP's `date()` function. See the documentation for available format codes.
  • `time`: A timestamp or a date/time string.

Example:

`{{#formattime: Y-m-d H:i:s | now}}` displays the current date and time.

Combining ParserFunctions

The real power of ParserFunctions comes from combining them to create complex logic. For example, you can use `#if` to conditionally execute `#expr` or `#time`.

Example:

`{{#if: Template:MarketOpen = true | Current time: {{#time: H:i:s}} | Market is closed}}`

This will display the current time if the `marketOpen` variable is set to "true", and it will display "Market is closed" otherwise.

Limitations

While ParserFunctions are powerful, they have limitations:

  • **Performance:** Complex ParserFunction calls can slow down page rendering. Avoid excessive use of nested functions.
  • **Complexity:** Writing complex logic with ParserFunctions can become difficult to read and maintain.
  • **Debugging:** Debugging ParserFunction code can be challenging.
  • **Recursion:** ParserFunctions do not support recursion.
  • **External Data:** They cannot directly access external data sources (e.g., databases, APIs).

Best Practices

  • **Keep it Simple:** Avoid overly complex expressions. Break down complex tasks into smaller, more manageable functions.
  • **Use Variables:** Use `#var` to store intermediate results and improve readability.
  • **Comment Your Code:** Add comments to explain the purpose of your ParserFunction calls. While comments are not officially supported, you can use HTML comments (``) which are ignored by the parser.
  • **Test Thoroughly:** Test your ParserFunction code with different inputs to ensure it behaves as expected.
  • **Consider Templates:** For complex logic or frequently used code, consider using Help:Templates instead of ParserFunctions. Templates often offer better performance and maintainability.

Resources

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