Extension:Expressions

MediaWiki extensions manual

Expressions Release status: stable
Implementation	Parser function
Description	Enhances the parser with boolean algebra.
Author(s)	Marijn van Wezel (Xxmarijnwtalk)
Latest version	1.5 (2021-10-19)
Compatibility policy	Master maintains backward compatibility.
MediaWiki	1.27+
PHP	5.6+
License	MIT License
Download	Download extension Git [?]: Download Git master browse repository (GitHub) commit history repository contributors (GitHub) code review
Hooks used ParserFirstCallInit
Quarterly downloads	3 (Ranked 128th)
Translate the Expressions extension if it is available at translatewiki.net

The Expressions extension enhances the wikitext parser with boolean algebra.

Usage

This extension introduces the parser function #expression. It evaluates an expression and returns one of two strings depending on the result:

{{#expression: expression | value if true | value if false }}

The available operators are listed below, in order of precedence. The extension makes use of type conversion when comparing two values. Non-empty strings are converted to true, zero is converted to false, and any integers that are not zero get converted to true.

{{#expression: "foobar" |1|0}} → 1

{{#expression: "a" == true |1|0}} → 1

{{#expression: 1 == true |1|0}} → 1

{{#expression: "foobar" or false |1|0}} → 1

{{#expression: "foobar" and false |1|0}} → 0

Two values can be compared before type juggling using the strict equality operator (===):

{{#expression: "a" === "a" |1|0}} → 1

{{#expression: "a" === true |1|0}} → 0

Operator associativity

Operator associativity determines how operators of the same precedence are grouped in the absence of parentheses. If a value (operand) is both preceded and followed by operators of the same precedence (for example == "a" ==), then the value can be applied to two different operations. Operator associativity determines which of those operations gets chosen.

All operators in the Expressions extension are left-associative. This means that all operators are grouped from left to right.

{{#expression: "a" == "b" == "c" == "d" |1|0}} → {{#expression: (("a" == "b") == "c") == "d" |1|0}} → {{#expression: (true == "c") == "d" |1|0}} → {{#expression: true == "d" |1|0}} → 1

{{#expression: "a" === "a" === "a" |1|0}} → {{#expression: ("a" === "a") === "a" |1|0}} → {{#expression: true === "a" |1|0}} → 0

The resulting behaviour might not be what you expect at first, therefore it is important to keep it in mind.

Type operators

Some operators are strictly typed and require their operand(s) to be of a certain type or else an error will occur. The table below lists all typed operators with their required type(s).

Operator	Required type(s)
>=	number >= number
<=	number <= number
>	number > number
<	number < number
~ !	~boolean !boolean
-	-number

When something other than the required type is used, the evaluator will throw an exception.

Operators

The table below lists all operators, in order of precedence from highest to lowest. Operands of the same type have identical precedence. Operations applied by operators of higher precedence will be evaluated first.

Type	Operators
Grouping (parentheses)	( )
Numbers, strings and booleans	1234.5 10 40298234
	"foobar" "lorem ipsum"
	true false
Unary	~ !
	-
Comparison	> < >= <=
Xor	xor
Conjunction	/\ && and
Disjunction	\/ or
Implication	=> ->
Equality, inequality, strict equality and strict inequality	==
	!=
	=== <-> <=>
	!== !<-> !<=> <>

Installation

• Download and place the file(s) in a directory called Expressions in your extensions/ folder.
• Add the following code at the bottom of your LocalSettings.php file:

  wfLoadExtension( 'Expressions' );
  

•  Done – Navigate to Special:Version on your wiki to verify that the extension is successfully installed.

See also

• Extension:ParserFunctions - Enhances parser with logical and string functions