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Extension:LoopFunctions

From mediawiki.org
MediaWiki extensions manual
LoopFunctions
Release status: stable
Implementation Parser function
Description Provides limited looping functionality in wikitext
Author(s)
Latest version 2020-03-26
MediaWiki 1.35+
PHP 5.3+
Database changes No
License GNU General Public License 2.0 or later
Download
Quarterly downloads 5 (Ranked 127th)
Translate the LoopFunctions extension if it is available at translatewiki.net

The LoopFunctions extension will enable limited looping functionality in the wikitext, where a variable ($n$ by default) is replaced by the current iteration number of the loop. The variable can be used in a plain text or link. Also the result of the whole loop can be put in an expression, e.g. to compute a factorial. However, the loop body is evaluated before replacing the variable, so e.g. a computation inside the loop body, depending on the value of the variable, is not possible.

Per standard the number of iterations is limited to 100 iterations per session.

Functions[edit]

#for[edit]

{{#for: n | text }}

Where n is the count of iteration and the text is the text to be repeated.

{{#for: n | text | replacement parameter }}

If, after expansion of templates, parser functions, and variables, the text contains the text $n$ or what is defined by the third parameter, that will be replaced by the current iteration, starting with 1.

Using in templates[edit]

Calling the template {{foo | n=4 | list1=a | list3=c | list4=d }}, if template foo containing: {{#for: {{{n}}} | {{{list$n$}}}<br/>}}, will result in the wikitext: a<br/>b<br/>c<br/>d<br/>

Using for calculations[edit]

Sum of squares 1^2 through 5^2: {{#expr:{{#for:5|+$n$*$n$}}}} gives 55

Factorial 6 (6!): {{#expr:1{{#for:6|*$n$}}}} gives 720

Compare, using m:Template:for and m:Template:plus square: {{#expr:{{for|call=plus square|pv=1|1|2|3|4|5}}}} gives 55; For a list of squares it seems that we can only use for, not #for.

Limitation[edit]

In the loop body, templates, parser functions, and variables are expanded before replacing the index variable by its values, i.e.:

Parameter of a parser function depending on the index variable
  • Code {{#for:3|{{lc:Ab$n$}}}} gives ab1ab2ab3; the result is in this case the same as when the repetition was done first, and then the evaluation of each item.
  • Code {{#for:3|{{uc:Ab$n$}}}} gives AB$N$AB$N$AB$N$; the result is in this case not the same, because $n$ is changed to $N$, and therefore not treated as index variable.
  • Applying #expr to an expression containing the index variable does not work: expansion of #expr in e.g. {{#expr:2*$n$}} gives the text so this text will be repeated: Expression error: Unrecognised punctuation character "$"
Template name depending on the index variable
  • Code {{#for:3|{{a$n$}}}} gives:
    • if the template with the literal name Template:a$n$ does not exist: Template:a1 Template:a2 Template:a3 (the loop body is evaluated as Template:a$n$, after which the loop function repeats that, substituting $n$).
    • if the template with the literal name Template:a$n$ does exist: the result of {{a*$n$}}{{a*$n$}}{{a*$n$}}, i.e., the content is repeated unchanged.
Limitation in combination with Extension:Variables
Within the loop a variable can be assigned a value depending on the loop variable, and the value of this variable can be retrieved.
However, it seems that within the loop the variable cannot be assigned a new value depending on its own current value. Instead the value on entering the loop is taken.

#foreach[edit]

Function only for template use.

{{#foreach: mask | text }}

{{#foreach: mask | text | replacement parameter }}

The mask is a string in the format prefix$n$suffix where $n$ can be changed via the replacement parameter. The function #foreach, called inside a template, will produce the text for $n$ = 1, 2, 3,... as long as prefix$n$suffix is a template parameter defined in the template call.

If the text contains the text $n$ or what is defined by the third parameter, that will be replaced by the current value of $n$.

It seems that the whole call of #foreach is ignored if the loop body contains a template call or a parser function call, or if the loop body does not contain {{{$n$}}}.

Example[edit]

Calling the template {{foo | foo2_bar=a | foo1_bar=b | a=12 | 6 | foo4_bar=c }} using the template foo, containing: {{#foreach: foo$n$_bar | foo$n$_bar = {{{foo$n$_bar}}}<br/>}} will result in the expanded wikitext foo1_bar = b<br/>foo2_bar = a<br/> and hence the output:

foo1_bar = b
foo2_bar = a

Since foo3_bar is not defined, foo4_bar is not listed either; neither are a and 1, the parameter names which exist but do not match the pattern.

Using without prefix or suffix[edit]

The code {{showpars | abc | de | w=fgh | ijk}} call Template:Showpars containing {{#foreach: $n$ | $n$ = {{{$n$}}}<br/>}} and gives:

1 = abc
2 = de
3 = ijk

Content of a template that links to the pages given by the values of the unnamed parameters:

{{#foreach:$n$|[[{{{$n$}}}]]<nowiki> </nowiki>}}

Installation[edit]

  • Download and move the extracted LoopFunctions folder to your extensions/ directory.
    Developers and code contributors should install the extension from Git instead, using:cd extensions/
    git clone https://gerrit.wikimedia.org/r/mediawiki/extensions/LoopFunctions
  • Add the following code at the bottom of your LocalSettings.php file:
    wfLoadExtension( 'LoopFunctions' );
    
  • Yes Done – Navigate to Special:Version on your wiki to verify that the extension is successfully installed.

See also[edit]