# Extension:LoopFunctions

MediaWiki extensions manual
LoopFunctions

Release status: stable

Implementation Parser function
Description provides limited looping functionality in wikitext
Author(s) Carl Fürstenberg, Matteo Cypriani
MediaWiki 1.7 or later
Database changes No

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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

### #for

```{{ #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

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

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

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

```{{ #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

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

```require_once "\$IP/extensions/LoopFunctions/LoopFunctions.php";