Module:Yesno

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.

Syntax

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.

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 {{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('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()

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')

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 nil for these inputs.

-- 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')

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:

yesno(nil)         -- Returns nil.
yesno('foo')       -- Returns nil.
yesno(nil, true)   -- Returns nil.
yesno(nil, false)  -- Returns nil.
yesno('foo', true) -- Returns true.

To get the binary true/false-only values, use code like:

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.

---

--  <nowiki>
--- Yesno module for processing of boolean-like wikitext input.
--  
--  It works similarly to the [[wikipedia:Template:Yesno|Yesno Wikipedia
--  template]]. This module is a consistent Lua interface for wikitext
--  input from templates.
--  
--  Wikitext markup used by MediaWiki templates only permit
--  string parameters like `"0"`, `"yes"`, `"no"` etc. As Lua
--  has a boolean primitive type, Yesno converts this
--  wikitext into boolean output for Lua to process.
--  
--  @script             yesno
--  @release            stable
--  @author             [[User:Dessamator|Dessamator]]
--  @attribution        [[wikipedia:User:ATDT|ATDT]]
--  @attribution        [[wikipedia:User:Mr. Stradivarius|Mr. Stradivarius]]
--  @attribution        [[wikipedia:Special:PageHistory/Module:Yesno|Other Wikipedia contributors]]
--  @see                [[wikipedia:Module:Yesno|Original module on
--                      Wikipedia]]
--  @see                [[Module:Yesno/testcases|Test cases for this
--                      module]]
--  @param              {?boolean|string} value Wikitext boolean-style
--                      or Lua boolean input.
--                       * Truthy wikitext input (`'yes'`, `'y'`, `'1'`,
--                      `'t'` or `'on'`) produces `true` as output.
--                       * The string representations of Lua's true
--                      boolean value (`'true'`) also produces `true`.
--                       * Falsy wikitext input (`'no'`, `'n'`, `'0'`,
--                      `'f'` or `'off'`) produces `false` as output.
--                       * The string representation of Lua's false
--                      boolean value (`'false'`) also produces `false`.
--                       * Localised text meaning `'yes'` or `'no'` also
--                      evaluate to `true` or `false` respectively.
--  @param[opt]         {?boolean|string} default Output to return if
--                      the Yesno `value` input is unrecognised.
--  @return             {?boolean} Boolean output corresponding to
--                      `val`:
--                       * The strings documented above produce a
--                      boolean value.
--                       * A `nil` value produces an output of `nil`.
--                      As this is falsy, additional logic may be needed
--                      to treat missing template parameters as truthy.
--                       * Unrecognised values return the `default`
--                      parameter. Blank strings are a key example
--                      of Yesno's unrecognised values and can evaluate
--                      to `true` if there is a default value.
local lower = mw.ustring.lower
local msg = mw.message.new

local yes = lower(msg('htmlform-yes'):plain())
local no = lower(msg('htmlform-no'):plain())
local en_yes = lower(msg('htmlform-yes'):inLanguage('en'):plain())
local en_no = lower(msg('htmlform-no'):inLanguage('en'):plain())

return function(value, default)
    value = type(value) == 'string' and lower(value) or value

    if value == nil then
        return nil

    elseif value == true
        or value == yes
        or value == en_yes
        or value == 'y'
        or value == 'true'
        or value == 't'
        or value == 'on'
        or value == 'enable'
        or tonumber(value) == 1
    then
        return true

    elseif value == false
        or value == no
        or value == en_no
        or value == 'n'
        or value == 'false'
        or value == 'f'
        or value == 'off'
        or value == 'disable'
        or tonumber(value) == 0
    then
        return false

    else
        return default
    end
end
--  </nowiki>