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This module is used to standardize the way modules interpret the boolean input of true and false as wikicode templates can only express boolean values through strings such as "yes", "no", etc. It also returns nil values as nil, to allow for distinctions between nil and false.


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.

local yesno = require('Module:Yesno')

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

<source lang="lua"> -- These always return true: yesno('yes') yesno('y') yesno('true') yesno('1') yesno(1) yesno(true)

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

-- A nil value always returns nil: yesno(nil) </syntaxhighlight>

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

<source 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>

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(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.
-- Copied from the English Wikipedia:

return function (val, default)
	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 tonumber(val) == 1
		return true
	elseif val == false
		or val == 'no'
		or val == 'n'
		or val == 'false'
		or tonumber(val) == 0
		return false
		return default