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== Usage ==
OPEN PRIVATE
First, load the module. Note that it can only be loaded from other Lua modules, not from normal wiki pages. For normal wiki pages you can use {{tl|yesno}} instead.
<syntaxhighlight lang="lua">
local yesno = require('Module:Yesno')
</syntaxhighlight>
Some input values always return <code>true</code>, and some always return <code>false</code>. <code>nil</code> values always return <code>nil</code>.
<syntaxhighlight lang="lua">
-- These always return true:
yesno('yes')
yesno('y')
yesno('true')
yesno('t')
yesno('on')
yesno('1')
yesno(1)
yesno(true)
-- These always return false:
yesno('no')
yesno('n')
yesno('false')
yesno('f')
yesno('off')
yesno('0')
yesno(0)
yesno(false)
-- A nil value always returns nil:
yesno(nil)
yesno()
</syntaxhighlight>
String values are converted to lower case before they are matched:
<syntaxhighlight lang="lua">
-- These always return true:
yesno('Yes')
yesno('YES')
yesno('yEs')
yesno('Y')
yesno('tRuE')
-- These always return false:
yesno('No')
yesno('NO')
yesno('nO')
yesno('N')
yesno('fALsE')
</syntaxhighlight>
===Undefined input ('foo')===
You can specify a default value if yesno receives input other than that listed above. If you don't supply a default, the module will return <code>nil</code> for these inputs.
<syntaxhighlight lang="lua">
-- These return nil:
yesno(nil)
yesno('foo')
yesno({})
yesno(5)
yesno('')
yesno(function() return 'This is a function.' end)
yesno(nil, true)
yesno(nil, 'bar')
-- These return true:
yesno('foo', true)
yesno({}, true)
yesno(5, true)
yesno('', true)
yesno(function() return 'This is a function.' end, true)
-- These return "bar":
yesno('foo', 'bar')
yesno({}, 'bar')
yesno(5, 'bar')
yesno('', 'bar')
yesno(function() return 'This is a function.' end, 'bar')
</syntaxhighlight>
Although the empty string usually evaluates to false in wikitext, it evaluates to true in Lua. This module prefers the Lua behaviour over the wikitext behaviour. If treating the empty string as false is important for your module, you will need to convert empty strings to a value that evaluates to false before passing them to this module. In the case of arguments received from wikitext, this can be done by using [[Module:Arguments]].
===Handling nil results===
By definition
:<syntaxhighlight lang="lua">
yesno(nil) -- Returns nil.
yesno('foo') -- Returns nil.
yesno(nil, true) -- Returns nil.
yesno(nil, false) -- Returns nil.
yesno('foo', true) -- Returns true.
</syntaxhighlight>
To get the binary <syntaxhighlight lang="lua" inline>true/false</syntaxhighlight>-only values, use code like:
<syntaxhighlight lang="lua">
myvariable = yesno(value) or false -- When value is nil, result is false.
myvariable = yesno(value) or true -- When value is nil, result is true.
myvariable = yesno('foo') or false -- Unknown string returns nil, result is false.
myvariable = yesno('foo', true) or false -- Default value (here: true) applies, result is true.
</syntaxhighlight><!--
--><includeonly>{{sandbox other||
[[Category:Lua metamodules]]
}}</includeonly>
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