Help:ParserFunctions

From Homestar Runner Wiki

Revision as of 21:34, 29 January 2021

This wiki has an extension installed called ParserFunctions. ParserFunctions are operators that take strings of text or numbers and perform logical or mathematical operators on them. They are often used in templates, to display current times and dates, and to generate random information. Here's how to use them:

#expr:

{{#expr:}} solves mathematical expressions. It only works with numerical entries; if you want to use strings, see #ifeq.

#if:

The {{#if:}} function is an if-then-else system. If the condition string is empty, it returns the "else text". If it is not empty, it returns the "then text". The syntax is:

{{#if: <condition string> | <then text> | <else text> }}

Its most common usage is in templates, where if the user defines a parameter, then it returns some prescribed text. If the user does not specify the parameter, it returns a default. Example:

{{#if: {{{parameter|}}} | Parameter is defined | Parameter is not defined }}

If the user types {{templatename|parameter=true}} or something similar, the result is "Parameter is defined". However, if they type {{templatename}}, the result is "Parameter is not defined". Note in the above example that the expression is a special function that returns the value of the parameter if it has been defined and returns the text to the right of the vertical bar (|) if the parameter has not been defined.

{{#if:}} does not solve expressions. For example, if you type {{#if: 30 - 30 = 50 | 1 | 0 }}, the result will be 1, since 30 - 30 = 50 is not empty. If you want to do if-then-else using expressions, see #ifexpr.

#ifeq:

{{#ifeq:}} compares two strings and then performs an if-then-else process. To use:

{{#ifeq: <text 1> | <text 2> | <if equal> | <if not equal> }}

If text 1 and text 2 are equal, then it returns the <ifequal> text. Otherwise, it returns the <ifnotequal> text.

Some examples:

• {{#ifeq: {{NAMESPACE}} | Help | This page is in the Help Namespace | This page is not in the Help Namespace }} shows up as This page is in the Help Namespace.
• {{#ifeq: 7 | +000007.0 | Seven = Seven | Seven is not equal to Seven }} shows up as Seven = Seven

In this above example, notice that {{#ifeq:}} can treat numbers as well as strings.

{{#ifeq:}} is case-sensitive:

{{#ifeq: capital | Capital | Equal | Not Equal }} shows up as Not Equal.

#ifexist:

{{#ifexist:}} performs an if-then-else process depending on whether a page exists. Syntax:

{{#ifexist: <page name> | <if exists> | <if does not exist> }}

{{#ifexist:}} does not work with interwiki links.

Example:

{{#ifexist: sbemail | [[Strong Bad Email]] | [[Main Page]] }} returns Strong Bad Email because a page named "sbemail" does exist.

#ifexpr:

{{#ifexpr:}} is an if-then-else routine that, like {{#expr:}}, can only be used with numbers. Syntax:

{{#ifexpr: <expression> | <if true> | <if false> }}

Some examples:

• {{#ifexpr: 7 + 8 = 15 | yes | no }} returns yes.
• {{#ifexpr: 7 + 8 = 78 | yes | no }} returns no.
• {{#ifexpr: {{PAGENAME}} = ParserFunctions | This is a help page | No}} returns the error Expression error: Unrecognised word "parserfunctions" because "ParserFunctions" (the text returned by {{PAGENAME}}) is a string, not a number.

#switch:

{{#switch:}} compares a number or a string against many items, and returns a result corresponding to the item it matches. Syntax:

{{#switch: <value>
| <result 1> = <text if 1 is true>
| <result 2> = <text if 2 is true>
| <result 3> = <text if 3 is true>
| <result 4> = <text if 4 is true>
| #default = <default value if none are true>
}}

If <value> matches <result 2>, for example, <text if 2 is true> will be returned by the function. If <value> does not match any of the first four items, <default value if none are true> will be returned.

"| <result n> = <text if n is true>" can be repeated as many times as necessary. However, "#default" can only be used once.

It is also possible to have "fall-through":

{{#switch: <value>
| <result 1>
| <result 2>
| <result 3> = <text if 1, 2, or 3 is true>
| <result 4> = <text if 4 is true>
| #default = <default value if none are true>
}}

<result 1> and <result 2> do not have equal signs, and if <value> matches either of them, the text corresponding to <result 3> will be returned.

Example:
{{#switch: {{#rand: 1|10}}
|1
|2
|3
|4
|5= This number is 1-5
|6= This number is 6
|7= This number is not 8
|8= This number is 1 more than 7
|9
|10= This is either 9 or 10
}}

turns out as This number is 1-5.

#time:

{{#time:}} is used for time and date formatting. It can be used to show the current time or day, or a set time or day in a certain format. Either way, here are the codes (following UTC):

If any input other than those discussed above is provided, it will pass through the function unmodified. So, links and punctuation can be easily used with this function. Examples:

• {{#time: l j F Y }} generates Tuesday 16 April 2024.
• {{#time: m/Y }} generates 04/2024.
• {{#time: H:i | - 6 hours}} generates 02:23, 6 hours before the current time
• {{#time: l Y-m-d }} generates Tuesday 2024-04-16.
• {{#time: l }} generates Tuesday.
• {{#time: z | 20071031}} generates 303, Halloween in "z" format

#rand:

{{#rand:}} generates a random integer. (It has been discontinued in standard versions of ParserFunctions, but the Homestar Runner Wiki uses a custom version that includes {{#rand:}}.) Syntax:

{{#rand: <minimum> | <maximum> }}

The minimum is the smallest integer it can generate, the maximum is the largest.

Examples:

• {{#rand: 1 | 50 }} generates 33.
• {{#rand: 1 | 500000 }} generates 289644.
• {{#rand: -10 | -1 }} generates -8.
• {{#rand: .1 | .9 }} generates 0, because it rounds the magnitude of the input down to the nearest integer (in this example, both the minimum and maximum values are 0).

#count:

count is a parser function that returns an integer that increments each time the function is called.

For more information please read the Counter help page.

#navlist:

{{#navlist:}} looks up a value from a list on a template and returns a value from the list, usually the next or previous value in the list, for use in navigation templates.

{{#navlist: <template name> | <action> | <lookup value> }}

• template name — Must be a name of a valid wiki template (Template: prefix not necessary). A malformed template name or nonexistent template will cause an error.
• action — Optional (default: next). Can be next, prev, or an integer.
• lookup value — Optional (default: the name of the page on which the parser function [or a containing template] is placed). If specified, must be a valid list item. If not specified, the name of the page on which the parser function (or a containing template) is placed must be a valid list item.

Action

• next or 1 or +1 returns the value in the list immediately after the lookup value. If there is no value after the lookup value, it returns the first value in the list.
• prev or -1 returns the value in the list immediately before the lookup value. If there is no value before the lookup value, it returns the last value in the list.
• n or +n will return the nth item after the lookup value (converted to an integer, limit: 1000). If it reaches the end of the list, it will wrap around to the beginning.
• -n will return the nth item before the lookup value (converted to an integer, limit: -1000). If it reaches the beginning of the list, it will wrap around to the end.
• 0 or a numeric value that converts to 0 will return the lookup value itself.
• An invalid action or a numeric value that's out of range will return an error.

Template setup

The template should consist of a simple bulleted list. A template without a list will cause an error. Each item in the list must potentially be a valid wiki title (although it doesn't necessarily have to be a valid wiki page). Do not use brackets. Any invalid characters in the page name portion of a list item will cause an error.

A pipe can be used to return a value other than the page name.

The template can have other paragraphs or explanatory text. Only list items (wherever they appear outside <noinclude> sections) are parsed.

* List of
* Page
* Names
* Page name | Return value

<noinclude>

Explanatory text.

* This list
* Will NOT be included

</noinclude>

Examples

The {{charnav-lookup}} template contains the following list:

• {{#navlist: charnav-lookup | next | Homestar Runner }} generates Strong Bad.
• {{#navlist: charnav-lookup | | Homestar Runner }} generates Homestar Runner.
• {{#navlist: charnav-lookup | next }} generates Strong Bad if the parser function (or a containing template) is placed on the Homestar Runner page.
• {{#navlist: charnav-lookup }} generates Strong Bad if the parser function (or a containing template) is placed on the Homestar Runner page.

• {{#navlist: charnav-lookup | prev | Strong Bad }} generates Homestar Runner.
• {{#navlist: charnav-lookup | prev }} generates Homestar Runner if the parser function (or a containing template) is placed on the Strong Bad page.

• {{#navlist: charnav-lookup | next | Homsar }} generates Homestar Runner.
• {{#navlist: charnav-lookup | | Homsar }} generates Homsar.
• {{#navlist: charnav-lookup | next }} generates Homestar Runner if the parser function (or a containing template) is placed on the Homsar page.
• {{#navlist: charnav-lookup }} generates Homestar Runner if the parser function (or a containing template) is placed on the Homsar page.

• {{#navlist: charnav-lookup | prev | Homestar Runner }} generates Homsar.
• {{#navlist: charnav-lookup | prev }} generates Homsar if the parser function (or a containing template) is placed on the Homestar Runner page.

• {{#navlist: charnav-lookup | +2 | Homestar Runner }} generates The Cheat.
• {{#navlist: charnav-lookup | 2.9 | Homestar Runner }} generates The Cheat.
• {{#navlist: charnav-lookup | -2 | Homestar Runner }} generates The Poopsmith.
• {{#navlist: charnav-lookup | 951 | Homestar Runner }} generates Strong Mad.
• {{#navlist: charnav-lookup | 0 | Homestar Runner }} generates Homestar Runner.

• {{#navlist: Template:charnav-lookup | next | Homestar Runner }} generates Strong Bad. (Using the Template: prefix is valid.)
• {{#navlist: not-a-real-tempate | next | Homestar Runner }} generates INVALID TEMPLATE NAME.
• {{#navlist: charnav | next | Homestar Runner }} generates INVALID LIST. (Note that {{charnav}} is a valid template but doesn't contain a list)

• {{#navlist: charnav-lookup | invalid | Homestar Runner }} generates INVALID ACTION.
• {{#navlist: charnav-lookup | 10000 | Homestar Runner }} generates ACTION OFFSET OUT OF RANGE.

• {{#navlist: charnav-lookup | next | Not in the List }} generates INVALID LOOKUP VALUE.
• {{#navlist: charnav-lookup | next }} generates INVALID LOOKUP VALUE if the parser function (or a containing template) is not placed on a page in the list.

See Also

• Meta's page on ParserFunctions
• Parser functions in templates