View source for Template:List lookup helper

<includeonly>{{#ifeq:{{#var:page_name}}|{{{1}}}|<!--
If page name is previously defined AND it equals arg1 then this invocation of the template can be skipped. This maintains the invariant of "loaded exactly once" if this is transcluded in another template that is itself transcluded multiple times.
-->|{{Add|invocations|1}}{{#vardefine:page_name|{{{1}}}}}{{#vardefine:loaded_page|{{:{{#var:page_name}}}}}}{{#vardefine:cleaned_page|{{#explode:{{#var:loaded_page}}|==|0}}}}{{#vardefine:minindex|0}}{{#vardefine:maxindex|1}}<!--
Find the upper bound of the size in steps of 2^n
-->{{#while:
|{{#explode:{{#var:cleaned_page}}|*|{{#var:maxindex}}|1000}}
|{{#vardefine:minindex|{{#var:maxindex}}}}{{Multiply|maxindex|2}}
}}{{#vardefine:index|{{#expr:floor(({{#var:maxindex}}+{{#var:minindex}})/2)}}}}<!--
Perform a binary search between [2^n-1, 2^n] to find the last element of the list
-->{{#while:
|{{#ifexpr:{{#var:minindex}}+1<{{#var:maxindex}}|true}}
|{{#if:{{#explode:{{#var:cleaned_page}}|*|{{#var:index}}|1000}}
<!--undershoot-->|{{#vardefine:minindex|{{#var:index}}}}
<!-- overshoot-->|{{#vardefine:maxindex|{{#var:index}}}}
}}
{{#vardefine:index|{{#expr:floor(({{#var:maxindex}}+{{#var:minindex}})/2)}}}}
}}{{Copy|index|length}}<!--
-->{{#loop:ii|1|{{#var:length}}|{{#vardefine:entry_{{#var:ii}}|{{#explode:{{#var:cleaned_page}}|*|{{#var:ii}}|1000}}}}}}}}</includeonly><noinclude>
{{Template doc|
Given a list page, loads it exactly once and sets up enough variables it will not need to be loaded again to retrieve any entry. If this template has been invoked before with the same page_name, no-op.
* page_name - the page name provided as arg1
* loaded_page - the text of page_name
* cleaned_page - the text of page_name before the first section header ("<nowiki>==</nowiki>")
* length - the length of the list
* entry_i - the entry in the list at position ''i'', where i is in <nowiki>[1, length-1]</nowiki> (0-indexed)

There is also the housekeeping variable "invocations", which equals the number of times this template was resolved and should thus always be 1.

<pre>
{{:QBWiki:Quick links/lingo}}
{{List lookup helper|QBWiki:Quick links/lingo}}
{{#var:cleaned_page}}
{{#var:length}}, {{#var:invocations}}

{{#loop:jj|1|{{#var:length}}|{{#var:entry_{{#var:jj}}}}<br/>}}
</pre>

{{:QBWiki:Quick links/lingo}}
{{List lookup helper|QBWiki:Quick links/lingo}}
{{#var:cleaned_page}}
{{#var:length}}, {{#var:invocations}}

{{#loop:jj|1|{{#var:length}}|{{#var:entry_{{#var:jj}}}}<br/>}}
}}</noinclude>