Extension: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 | |
| 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 }}
{{ #for: n | text | replacement parameter }}
where n is the count of iteration and the text is the text to be repeated. 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.
Examples[edit]
calling the template {{ foo: |n=4 | list1=a | list2=b | list3=c | list4=d }}
using the template foo, containing: {{ #for: {{{n}}} | {{{list$n$}}}<br/> }}
will result in the text
a<br/>b<br/>c<br/>d<br/>
- 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.
Examples:
Parameter of a parser function depending on the index variable:
- {{#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.
- {{#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 "Expression error: Unrecognised punctuation character "$"", so this text will be repeated.
Template name depending on the index variable:
- {{#for:3|{{a$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[edit]
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]
{{ #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 {{{$n$}}}.
Examples[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.
Example without prefix or suffix:
The call {{showpars | abc | de | w=fgh | ijk }} of Template:Showpars containing {{ #foreach: $n$ | $n$ = {{{$n$}}}<br/> }} 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 place the file(s) in a directory called
LoopFunctionsin yourextensions/folder. - Add the following code at the bottom of your
LocalSettings.php:wfLoadExtension( 'LoopFunctions' );
Done – Navigate to Special:Version on your wiki to verify that the extension is successfully installed.
To users running MediaWiki 1.30 or earlier:
The instructions above describe the new way of installing this extension using wfLoadExtension().
If you need to install this extension on these earlier versions (MediaWiki 1.30 and earlier), instead of wfLoadExtension( 'LoopFunctions' );, you need to use:
require_once "$IP/extensions/LoopFunctions/LoopFunctions.php";