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本模块来自中文维基百科，使用cc by-sa 4.0授权，敬希注意。
This module provides a consistent interface for processing boolean or boolean-style string input. While Lua allows the <code>true</code> and <code>false</code> boolean values, wikicode templates can only express boolean values through strings such as "yes", "no", etc. This module processes these kinds of strings and turns them into boolean input for Lua to process. It also returns <code>nil</code> values as <code>nil</code>, to allow for distinctions between <code>nil</code> and <code>false</code>. The module also accepts other Lua structures as input, i.e. booleans, numbers, tables, and functions. If it is passed input that it does not recognise as boolean or <code>nil</code>, it is possible to specify a default value to return.

== Syntax ==

<pre lang="lua">yesno(value, default)</pre>

<code>value</code> is the value to be tested. Boolean input or boolean-style input (see below) always evaluates to either <code>true</code> or <code>false</code>, and <code>nil</code> always evaluates to <code>nil</code>. Other values evaluate to <code>default</code>.

== 用法 ==

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.

<pre lang="lua">
local yesno = require('Module:Yesno')
</pre>

Some input values always return <code>true</code>, and some always return <code>false</code>. <code>nil</code> values always return <code>nil</code>.

<pre lang="lua">
-- 當參數是"yes"或其等效字串時將回傳"真":
yesno('yes')
yesno('y')
yesno('true')
yesno('1')
yesno(1)
yesno(true)

-- 當參數是"no"或其等效字串時將回傳"假":
yesno('no')
yesno('n')
yesno('false')
yesno('0')
yesno(0)
yesno(false)

-- 當參數是nil時將回傳nil:
yesno(nil)
</pre>

第1個參數將忽視大小寫:

<pre 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')
</pre>

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.

<pre lang="lua">
-- These return nil:
yesno('foo')
yesno({})
yesno(5)
yesno(function() return 'This is a function.' end)

-- These return true:
yesno('foo', true)
yesno({}, true)
yesno(5, true)
yesno(function() return 'This is a function.' end, true)

-- These return "bar":
yesno('foo', 'bar')
yesno({}, 'bar')
yesno(5, 'bar')
yesno(function() return 'This is a function.' end, 'bar')
</pre>

Note that the blank string also functions this way:
<pre lang="lua">
yesno('')        -- Returns nil.
yesno('', true)  -- Returns true.
yesno('', 'bar') -- Returns "bar".
</pre>

Although the blank 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 blank string as false is important for your module, you will need to remove blank arguments at an earlier stage of processing.