Parser functions, added in MediaWiki 1.7, are a type of extension that integrate closely with the parser.The phrase "parser function" should not be confused withExtension:ParserFunctions, which is a collection of simple parser functions.(SeeHelp:Extension:ParserFunctions for those.)

Whereas atag extension is expected to take unprocessed text and return HTML to the browser, a parser function can 'interact' with other wiki elements in the page. For example, the output of a parser function could be used as atemplate parameter or in the construction of alink.

The typical syntax for a parser function is:

{{ #functionname: param1 | param2 | param3 }}

For more information, seethe documentation forParser::setFunctionHook($id,$callback,$flags=0).This documentation states:

The callback function should have the form:

function myParserFunction( $parser, $arg1, $arg2, $arg3 ) { ... }

Or withSFH_OBJECT_ARGS:

function myParserFunction( $parser, $frame, $args ) { ... }

The first variant of the call passes all arguments as plain text.The second passes all arguments as an array ofPPNodes, except for the first ($args[0]), which is currently text, though this may change in the future.These represent the unexpanded wikitext.The$frame parameter can be used to expand these arguments as needed.This is commonly used for conditional processing so that only thetrue case is evaluated with anif- orswitch-like parser function.The frame object can also climb up the document tree to get information about the caller and has functions to determine and manage call depth, time-to-live, and whether the result of the parser function is volatile.

Creating a parser function is slightly more complicated than creating a new tag because the function name must be amagic word, a keyword that supports aliases and localization.

Below is an example of an extension that creates a parser function.

The registration goes intoextension.json and the code intosrc/ExampleExtensionHooks.php respectively:

{"name":"ExampleExtension","author":"Me","version":"1.0.0","url":"https://www.mediawiki.org/wiki/Extension:ExampleExtension","descriptionmsg":"exampleextension-desc","license-name":"GPL-2.0-or-later","type":"parserhook","MessagesDirs":{"ExampleExtension":["i18n"]},"AutoloadClasses":{"ExampleExtensionHooks":"src/ExampleExtensionHooks.php"},"ExtensionMessagesFiles":{"ExampleExtensionMagic":"ExampleExtension.i18n.php"},"Hooks":{"ParserFirstCallInit":"ExampleExtensionHooks::onParserFirstCallInit"},"manifest_version":1}

{"name":"ExampleExtension","author":"Me","version":"1.0.0","url":"https://www.mediawiki.org/wiki/Extension:ExampleExtension","descriptionmsg":"exampleextension-desc","license-name":"GPL-2.0-or-later","type":"parserhook","MessagesDirs":{"ExampleExtension":["i18n"]},"AutoloadClasses":{"ExampleExtensionHooks":"src/ExampleExtensionHooks.php"},"ExtensionMessagesFiles":{"ExampleExtensionMagic":"ExampleExtension.i18n.php"},"Hooks":{"ParserFirstCallInit":"onParserFirstCallInit"},"HookHandlers":{"ExampleExtensionHooks":{"class":"MediaWiki\\Extension\\ExampleExtension\\Hooks"}},"manifest_version":1}

<?phpclassExampleExtensionHooks{// Register any render callbacks with the parserpublicstaticfunctiononParserFirstCallInit(Parser$parser){// Create a function hook associating the <code>example</code> magic word with renderExample()$parser->setFunctionHook('example',[self::class,'renderExample']);}// Render the output of {{#example:}}.publicstaticfunctionrenderExample(Parser$parser,$param1='',$param2='',$param3=''){// The input parameters are wikitext with templates expanded.// The output should be wikitext too.$output="param1 is$param1 and param2 is$param2 and param3 is$param3";return$output;}}

<?phpclassExampleExtensionHooksimplementsParserFirstCallInitHook{// Register any render callbacks with the parserpublicfunctiononParserFirstCallInit($parser){// Create a function hook associating the <code>example</code> magic word with renderExample()$parser->setFunctionHook('example',[$this,'renderExample']);}// Render the output of {{#example:}}.publicfunctionrenderExample($parser,$param1='',$param2='',$param3=''){// The input parameters are wikitext with templates expanded.// The output should be wikitext too.$output="param1 is$param1 and param2 is$param2 and param3 is$param3";return$output;}}

Another file,ExampleExtension.i18n.php, in your extension directory (Not in the src/ subdirectory) should contain:

<?php/** * @license GPL-2.0-or-later * @author Your Name (YourUserName) */$magicWords=[];/** English * @author Your Name (YourUserName) */$magicWords['en']=['example'=>[0,'example'],];

With this extension enabled,

• {{#example: hello | hi | hey}}

produces:

• param1 is hello and param2 is hi and param3 is hey

MediaWiki\MediaWikiServices::getInstance()->getContentLanguage()->mMagicExtensions['wikicodeToHtml']=['MAG_CUSTOM','custom'];

Magic words and their handling parser functions can be defined entirely in LocalSettings.php.

$wgHooks['ParserFirstCallInit'][]=function(Parser$parser){MediaWiki\MediaWikiServices::getInstance()->getContentLanguage()->mMagicExtensions['wikicodeToHtml']=['wikicodeToHtml','wikicodeToHtml'];$parser->setFunctionHook('wikicodeToHtml','wikicodeToHtml');};functionwikicodeToHtml(Parser$parser,$code=''){$title=$parser->getTitle();$options=$parser->Options();$options->enableLimitReport(false);$parser=$parser->getFreshParser();return[$parser->parse($code,$title,$options)->getText(),'isHTML'=>true];}

For longer functions, you may want to split the hook functions out to a _body.php or .hooks.php file and make them static functions of a class. Then you can load the class with$wgAutoloadClasses and call the static functions in the hooks; e.g.:

Put this in yourextension.json file:

"Hooks":{"ParserFirstCallInit":"ExampleExtensionHooks::onParserFirstCallInit"},"AutoloadClasses":{"ExampleExtensionHooks":"src/ExampleExtensionHooks.php"}

• See:writing an event handler for other styles.

Then put this in yoursrc/ExampleExtensionHooks.php file:

classExampleExtensionHooks{publicstaticfunctiononParserFirstCallInit(Parser$parser){$parser->setFunctionHook('example',[self::class,'renderExample']);}}

To have the wikitext returned by your parser function be fully parsed (including expansion of templates), set thenoparse option tofalse when returning:

return[$output,'noparse'=>false];

It seems the default value fornoparse changed fromfalse totrue, at least in some situations, sometime around version 1.12.

Conversely, to have your parser function return HTML that remains unparsed, rather than returning wikitext, use this:

return[$output,'noparse'=>true,'isHTML'=>true];

By default, MW adds a hash character (number sign,#) to the name of each parser function.To suppress that addition (and obtain a parser function with no# prefix), include theSFH_NO_HASH constant in the optional flags argument to setFunctionHook, as describedbelow.

When choosing a name without a hash prefix, note that transclusion of a page with a name starting with that function name followed by a colon is no longer possible. In particular, avoid function names equal to a namespace name. In the case that interwiki transclusion[1] is enabled, also avoid function names equal to an interwiki prefix.

For more details of the interface into the parser, see the documentation for setFunctionHook in includes/Parser.php.Here's a (possibly dated) copy of those comments:

function setFunctionHook( $id, $callback, $flags = 0 )

Parameters:

• string $id - The magic word ID
• mixed $callback - The callback function (and object) to use
• integer $flags - Optional. Values:

• SFH_NO_HASH (1) constant if you call the function without#.
• SFH_OBJECT_ARGS (2) if you pass a PPFrame object and array of arguments instead of a series of function arguments, for whichsee above.
• Defaults to 0 (no flags).

Return value: The old callback function for this name, if any

Create a function, e.g.,{{#sum:1|2|3}}. The callback function should have the form:

functionmyParserFunction($parser,$arg1,$arg2,$arg3){...}

The callback may either return the text result of the function, or an array with the text in element 0, and a number of flags in the other elements. The names of the flags are specified in the keys. Valid flags are:

Some parser functions represent a significant use of a wiki's resources and should be marked as "expensive".The number of expensive parser functions on any given page is limited by the$wgExpensiveParserFunctionLimit setting.What counts as expensive is left up to the function itself, but typically, anything that is likely to cause a delay that extends beyond simple processing of data should be considered.This includes things like database reads and writes, launching a shell script synchronously, or file manipulation.On the other hand, not all such functions should necessarily be tagged.Semantic MediaWiki, for example, only marks a percentage of its database reads as expensive.This is due to the fact that on certain data-intensive pages, it could easily overflow the normal expensive parser function limits.In cases like this, the potential for noticeably slower performance that doesn't get flagged as expensive is a trade-off to having the functionality that SMW offers.

To mark your parser function as expensive, from within the body of the function's code, use$result=$parser->incrementExpensiveFunctionCount();.The return value will befalse if the expensive function limit has been reached or exceeded.

Parser functions do not support named parameters the way templates and tag extensions do, but it is occasionally useful to fake it. Users are often accustomed to using vertical bars (| ) to separate arguments, so it's nice to be able to do that in the parser function context, too. Here's a simple example of how to accomplish this:

functionExampleExtensionRenderParserFunction(&$parser){// Suppose the user invoked the parser function like so:// {{#myparserfunction: foo=bar | apple=orange | banana }}$options=extractOptions(array_slice(func_get_args(),1));// Now you've got an array that looks like this:// [foo] => 'bar'// [apple] => 'orange'// [banana] => true// Continue writing your code...}/** * Converts an array of values in form [0] => "name=value" * into a real associative array in form [name] => value * If no = is provided, true is assumed like this: [name] => true * * @param array string $options * @return array $results */functionextractOptions(array$options){$results=[];foreach($optionsas$option){$pair=array_map('trim',explode('=',$option,2));if(count($pair)===2){$results[$pair[0]]=$pair[1];}if(count($pair)===1){$results[$pair[0]]=true;}}return$results;}

General and related guides:

• Manual:Developing extensions, or for more general information about extensions, seeManual:Extensions andExtensions FAQ.
• Manual:Tag extensions
• Manual:Magic words

Code:

• Manual:Parser.php
• Manual:Hooks/ParserFirstCallInit
• Parser function hooks - an (incomplete) list of parser functions provided by core and extensions
• TheParser Hooks PHP library, which provides an object orientated interface for declarative parser hooks
• Manual:Extension data

Examples:

• TheParserFunctions extension is a well-known collection of parser functions.
• Help:Extension:ParserFunctions
• Category:Parser function extensions

• MediaWiki development
• Parser extensions
• Wiki markup
• Customization techniques
• Sample code