View source for Help:Parser functions

# Help:Parser functions

'''Parser functions''' are a powerful feature of MediaWiki that allow you to perform calculations, manipulate strings, and control the output of your wiki pages dynamically. They are essentially functions that operate on the wikitext before it is rendered into HTML. This allows you to create complex and reusable content, automate tasks, and add a level of interactivity to your wiki. This guide will serve as a beginner-friendly introduction to parser functions, covering their syntax, common uses, and some examples.

== What are Parser Functions?

At their core, parser functions are snippets of code embedded within your wikitext that are evaluated by the MediaWiki parser.  The result of the evaluation is then substituted into the page. They are denoted by a hash symbol (`#`) followed by the function name and any necessary arguments, enclosed in double curly braces (`{{...}}`).

For example: `{{#title:My Page}}` would output "My Page" with the first letter capitalized.

Parser functions are *not* programming languages in the full sense. They have a limited set of operations, primarily focused on text manipulation, mathematical calculations, and date/time handling.  They are designed for presentation and formatting, not for complex logic or data processing. For more complex tasks, consider using [[Extensions]].

== Basic Syntax

The general syntax of a parser function is:

`{{#function_name: argument1 | argument2 | ...}}`

*   `#`:  Indicates that this is a parser function call.
*   `function_name`: The name of the function you want to use (e.g., `title`, `if`, `expr`).  See the section on [Common Parser Functions](#common_parser_functions) for a list.
*   `argument1`, `argument2`, etc.: The inputs to the function.
*   `|`:  The pipe symbol separates the arguments.

Arguments can be:

*   **Literal values:**  e.g., `"Hello"`, `123`
*   **Wikitext variables:** e.g., `{{PAGENAME}}`, `{{CURRENTTIMESTAMP}}`
*   **Other parser function calls:**  You can nest parser functions within each other.
*   **Empty arguments:**  Represented by `|` without a value.

== Common Parser Functions

Here's a breakdown of some of the most commonly used parser functions.  This is not an exhaustive list, but it provides a good starting point.

*   **`#title`**:  Formats a string as a title, capitalizing the first letter of each word.  Useful for creating consistent headings.
    ```wiki
    {{#title:my awesome page}}  <!-- Outputs: My Awesome Page -->
    ```

*   **`#if`**:  A conditional statement. If the first argument evaluates to a non-empty string, it outputs the second argument; otherwise, it outputs the third argument (if provided).
    ```wiki
    {{#if:{{PAGENAME}} | This is the page {{PAGENAME}} | This page does not exist}}
    ```

*   **`#ifeq`**:  Checks if two arguments are equal.  Outputs the third argument if they are equal, otherwise outputs the fourth argument (if provided).
    ```wiki
    {{#ifeq:{{PAGENAME}} | Help:Parser functions | You are on the Parser functions help page! | You are not on the Parser functions help page.}}
    ```

*   **`#ifexist`**: Checks if a page exists. Outputs the second argument if the page exists, otherwise outputs the third argument (if provided).
    ```wiki
    {{#ifexist:Help:Parser functions | This page exists. | This page does not exist.}}
    ```

*   **`#expr`**:  Evaluates a mathematical expression.  Supports basic arithmetic operations (+, -, *, /, %), as well as some functions.  This is critical for [[Technical Analysis]] calculations.
    ```wiki
    {{#expr: 2 + 2}}  <!-- Outputs: 4 -->
    {{#expr: 10 / 3}} <!-- Outputs: 3.3333333333333 -->
    ```
    For more advanced calculations involving [[Moving Averages]] or [[Bollinger Bands]], `#expr` is essential.

*   **`#time`**: Formats a date and time according to a specified format string.  The first argument is the date/time string to format (often `{{CURRENTTIMESTAMP}}`), and the second argument is the format string. See [Manual:Time and date parameters](https://www.mediawiki.org/wiki/Manual:Time_and_date_parameters) for format string details. This is vital for tracking [[Trend Duration]].
    ```wiki
    {{#time: Y-m-d H:i:s | {{CURRENTTIMESTAMP}}}} <!-- Outputs: 2023-10-27 10:30:00 (example) -->
    ```

*   **`#formatdate`**: Similar to `#time`, but provides more flexibility and pre-defined formats.
    ```wiki
    {{#formatdate:long | {{CURRENTTIMESTAMP}}}} <!-- Outputs: October 27, 2023 (example) -->
    ```

*   **`#stringlength`**: Returns the length of a string.
    ```wiki
    {{#stringlength:Hello World}} <!-- Outputs: 11 -->
    ```

*   **`#subst`**:  Substitutes a template into the current page.  Unlike using a template directly (e.g., `{{TemplateName}}`), `#subst` replaces the template call with the *expanded* content of the template.
    ```wiki
    {{#subst:Template:Example}}
    ```

*   **`#switch`**:  A multi-way conditional statement.  It checks the first argument against a series of cases and outputs the corresponding result.  Useful for handling different scenarios based on a variable value.  Can be used to categorize different [[Trading Strategies]].
    ```wiki
    {{#switch: {{PAGENAME}}
      | Help:Parser functions = You are reading the Parser Functions help page.
      | Main Page = Welcome to the wiki!
      | #default = This is a different page.
    }}
    ```

*   **`#vardefine` and `#varbyname`**: These functions allow you to define and use named variables within a page.  This can improve readability and maintainability, especially when dealing with complex calculations or templates.  Think of them as local variables for your wiki page.  Crucial for implementing complex [[Indicator]] calculations.

    ```wiki
    {{#vardefine:myValue | 10}}
    {{#expr: {{varbyname:myValue}} + 5}} <!-- Outputs: 15 -->
    ```

== Advanced Techniques

*   **Nesting Parser Functions:**  You can combine parser functions to achieve more complex results.  For example:
    ```wiki
    {{#ifexist:{{PAGENAME}} | {{#title:{{PAGENAME}}}} | Page does not exist}}
    ```
    This checks if the current page exists, and if it does, formats the page title.

*   **Using with Templates:** Parser functions are often used within templates to create dynamic and reusable content.  Templates can accept arguments and use parser functions to process them. This is how complex [[Chart Patterns]] can be displayed.

*   **Looping (Limited):** While MediaWiki doesn't have explicit looping constructs, you can sometimes simulate looping behavior using recursion and `#if` statements, although this can be complex and resource-intensive.

* **Error Handling:**  Error handling within parser functions is limited.  `#expr` will often return an error message if the expression is invalid.  You can use `#if` to check for empty results and handle errors gracefully.

* **Performance Considerations:**  Excessive use of complex parser functions, especially nested ones, can impact page rendering performance.  Keep your functions as simple as possible and avoid unnecessary calculations.  Consider using [[Extensions]] for computationally intensive tasks.

== Examples in a Trading Context

Let's illustrate how parser functions can be used in a wiki dedicated to financial trading.

1.  **Calculating Profit/Loss:**

    ```wiki
    {{#expr: ({{BuyPrice}} - {{SellPrice}}) / {{BuyPrice}} * 100}}
    ```
    This calculates the percentage profit or loss, assuming you have defined variables `BuyPrice` and `SellPrice`.  This is fundamental for [[Backtesting]].

2.  **Risk/Reward Ratio:**

    ```wiki
    {{#expr: {{PotentialProfit}} / {{PotentialLoss}} }}
    ```
    Calculates the risk/reward ratio for a trade.

3.  **Displaying Time Until Expiration (for Options):**

    ```wiki
    {{#time: d | {{ExpirationDate}} | {{CURRENTTIMESTAMP}}}}
    ```
    Displays the number of days until an option expires. Important for [[Options Trading]].

4.  **Highlighting Significant Changes:**

    ```wiki
    {{#if: {{Change}} > 0 | <span style="color:green;">{{Change}}</span> | <span style="color:red;">{{Change}}</span> }}
    ```
    Highlights positive changes in green and negative changes in red. Useful for showing [[Market Sentiment]].

5. **Determining Trend Strength:**

   ```wiki
    {{#switch: {{RSI}}
      | > 70 = Overbought
      | < 30 = Oversold
      | #default = Neutral
    }}
   ```
   Classifies the Relative Strength Index (RSI) value.

6. **Calculating Fibonacci Retracement Levels:**

    ```wiki
    {{#expr: {{High}} - ({{High}} - {{Low}}) * 0.236}}
    {{#expr: {{High}} - ({{High}} - {{Low}}) * 0.382}}
    {{#expr: {{High}} - ({{High}} - {{Low}}) * 0.5}}
    ```
    Calculates common Fibonacci retracement levels. This is useful when identifying potential [[Support and Resistance Levels]].

7. **Displaying Moving Average Crossover Signals:**

    ```wiki
    {{#if: {{ShortMA}} > {{LongMA}} | Bullish Crossover | Bearish Crossover}}
    ```
    Displays a bullish or bearish crossover signal based on two moving averages.

8. **Evaluating Volatility:**

    ```wiki
    {{#expr: {{ATR}} / {{Close}} * 100}}
    ```
    Calculates the Average True Range (ATR) as a percentage of the closing price. This is a common measure of [[Market Volatility]].

9. **Identifying Breakout Points:**

    ```wiki
    {{#if: {{Close}} > {{Resistance}} | Breakout! | Below Resistance}}
    ```
    Checks if the closing price has broken through a resistance level.

10. **Calculating Sharpe Ratio (Simplified):**

    ```wiki
    {{#expr: ({{AverageReturn}} - {{RiskFreeRate}}) / {{StandardDeviation}} }}
    ```
    A simplified calculation of the Sharpe Ratio, a measure of risk-adjusted return.



== Limitations

*   **Limited Functionality:** Parser functions are not a full-fledged programming language. Their capabilities are limited to text manipulation, mathematical calculations, and date/time handling.
*   **Performance:**  Complex and nested parser functions can significantly impact page rendering performance.
*   **Error Handling:** Error handling is limited.
*   **Security:**  Be cautious when using user-supplied data within parser functions, as it could potentially lead to security vulnerabilities.
*   **Recursion Depth:** There is a limit to the recursion depth, so deeply nested functions may fail.



== Resources

*   [[Help:Templates]]
*   [[Help:Variables]]
*   [[Help:Categories]]
*   [MediaWiki Parser Functions Documentation](https://www.mediawiki.org/wiki/Manual:Parser_functions)
*   [Time and date parameters](https://www.mediawiki.org/wiki/Manual:Time_and_date_parameters)
*   [Technical Analysis](https://en.wikipedia.org/wiki/Technical_analysis)
*   [Moving Averages](https://en.wikipedia.org/wiki/Moving_average)
*   [Bollinger Bands](https://en.wikipedia.org/wiki/Bollinger_Bands)
*   [Trend Duration](https://www.investopedia.com/terms/t/trendanalysis.asp)
*   [Options Trading](https://www.investopedia.com/terms/o/optionstrading.asp)
*   [Chart Patterns](https://www.investopedia.com/terms/c/chartpattern.asp)
*   [Support and Resistance Levels](https://www.investopedia.com/terms/s/supportandresistance.asp)
*   [Market Sentiment](https://www.investopedia.com/terms/m/marketsentiment.asp)
*   [Market Volatility](https://www.investopedia.com/terms/v/volatility.asp)
*   [Fibonacci Retracement](https://www.investopedia.com/terms/f/fibonacciretracement.asp)
*   [Sharpe Ratio](https://www.investopedia.com/terms/s/sharperatio.asp)
*   [Risk Management](https://www.investopedia.com/terms/r/riskmanagement.asp)
*   [Trading Strategies](https://www.investopedia.com/terms/t/trading-strategy.asp)
*   [Backtesting](https://www.investopedia.com/terms/b/backtesting.asp)
*   [ATR (Average True Range)](https://www.investopedia.com/terms/a/atr.asp)
*   [RSI (Relative Strength Index)](https://www.investopedia.com/terms/r/rsi.asp)
*   [Breakout Trading](https://www.investopedia.com/terms/b/breakout.asp)
*   [Candlestick Patterns](https://www.investopedia.com/terms/c/candlestick.asp)
*   [Elliott Wave Theory](https://www.investopedia.com/terms/e/elliottwavetheory.asp)
*   [Ichimoku Cloud](https://www.investopedia.com/terms/i/ichimoku-cloud.asp)
*   [MACD (Moving Average Convergence Divergence)](https://www.investopedia.com/terms/m/macd.asp)
*   [Stochastic Oscillator](https://www.investopedia.com/terms/s/stochasticoscillator.asp)
*  [Gap Analysis](https://www.investopedia.com/terms/g/gap.asp)



[[Help:Contents]]

[[Help:Formatting]]

[[Help:Linking]]

[[Help:Templates]]

[[Help:Variables]]

[[Help:Categories]]

[[Manual:Configuration settings]]

[[Manual:Extension installation]]

[[Manual:Upgrading]]

[[Special:AllPages]]

[[Main Page]]

[[Category:Help]]
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