Mòideal:Yesno

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This module is subject to page protection. It is a highly visible module in use by a very large number of pages, or is substituted very frequently. Because vandalism or mistakes would affect many pages, and even trivial editing might cause substantial load on the servers, it is protected from editing.

This Lua module is used on many pages and changes may be widely noticed. Test changes in the module's /sandbox or /testcases subpages. Consider discussing changes on the talk page before implementing them.

This mòideal is used in system messages. Changes to it can cause immediate changes to the Wikipedia user interface. To avoid large-scale disruption, any changes should first be tested in this mòideal's /sandbox or /testcases subpage, or in your own user space. The tested changes can then be added in one single edit to this mòideal. Please discuss any changes on the talk page before implementing them.

This module provides a consistent interface for processing boolean or boolean-style string input. While Lua allows the true and false 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 nil values as nil, to allow for distinctions between nil and false. 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 nil, it is possible to specify a default value to return.

Yesno(value, default)

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

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 {{Yesno}} instead.

local Yesno = require('Module:Yesno')

Some input values always return true, and some always return false. nil values always return nil.

-- These always return true:
Yesno('yes')
Yesno('y')
Yesno('true')
Yesno('t')
Yesno('1')
Yesno(1)
Yesno(true)

-- These always return false:
Yesno('no')
Yesno('n')
Yesno('false')
Yesno('f')
Yesno('0')
Yesno(0)
Yesno(false)

-- A nil value always returns nil:
Yesno(nil)

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

-- 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')

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 nil for these inputs.

-- 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')

Note that the blank string also functions this way:

Yesno('')        -- Returns nil.
Yesno('', true)  -- Returns true.
Yesno('', 'bar') -- Returns "bar".

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.

-- Function allowing for consistent treatment of boolean-like wikitext input.
-- It works similarly to the template {{yesno}}.

return function (val, default)
	-- If your wiki uses non-ascii characters for any of "yes", "no", etc., you
	-- should replace "val:lower()" with "mw.ustring.lower(val)" in the
	-- following line.
	val = type(val) == 'string' and val:lower() or val
	if val == nil then
		return nil
	elseif val == true 
		or val == 'yes'
		or val == 'y'
		or val == 'true'
		or val == 't'
		or val == 'on'
		or tonumber(val) == 1
	then
		return true
	elseif val == false
		or val == 'no'
		or val == 'n'
		or val == 'false'
		or val == 'f'
		or val == 'off'
		or tonumber(val) == 0
	then
		return false
	else
		return default
	end
end