Editing Module:Yesno/doc (section)

== Usage ==

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.

<code><nowiki>
local yesno = require('Module:Yesno')
</nowiki></code>

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

<code><nowiki>
-- 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()
</nowiki></code>

String values are converted to lower case before they are matched:

<code><nowiki>
-- 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')
</nowiki></code>

===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.

<code><nowiki>
-- 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')
</nowiki></code>

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:
<code><nowiki>
yesno(nil)         -- Returns nil.
yesno('foo')       -- Returns nil.
yesno(nil, true)   -- Returns nil.
yesno(nil, false)  -- Returns nil.
yesno('foo', true) -- Returns true.
</nowiki></code>

To get the binary <code><nowiki>true/false</nowiki></code>-only values, use code like:
<code><nowiki>
myvariable = yesno(value or false) -- When value is nil, result is false.
myvariable = yesno(value or true)  -- When value is nil, result is true. (XXX: when value is false, 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.
</nowiki></code>

Better suggestions:
<code><nowiki>
local myvariable = yesno(value)
if myvariable == nil then -- value is nil or an unrecognized string
    myvariable = true
end

-- more efficient when value is nil, but more verbose
-- (note the default result has to be written twice)
local myvariable
if value == nil then
    myvariable = true
else
    myvariable = yesno(value, true)
end

-- Terse coding when the default is false:
myvariable = yesno(value or false, false)
-- if value is nil, yesno() is called with false instead; result is false.
-- If value is 'foo', yesno() is called with 'foo'; 'foo' makes no sense, so the default (false) is returned.
-- if value is 'yes' or 'no', yesno() is called with 'yes' or 'no'; result is true or false.

-- Terse coding when the default is true:
myvariable = yesno(value or true, true)
-- if value is nil, yesno() is called with true instead; result is true.
-- If value is 'foo', yesno() is called with 'foo'; 'foo' makes no sense, so the default (true) is returned.
-- if value is 'yes' or 'no', yesno() is called with 'yes' or 'no'; result is true or false.
</nowiki></code><!--
--><includeonly>{{sandbox other||
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<noinclude>
</noinclude>
<includeonly>
[[Category:Utility modules]]
</includeonly>