Module:Yesno/sandbox

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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. (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.

Better suggestions:

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.

The above documentation is transcluded from Module:Yesno/doc. (edit | history)
Editors can experiment in this module's sandbox (edit | diff) and testcases (edit | run) pages.
Add categories to the /doc subpage. Subpages of this module.

--- Allows for consistent treatment of boolean-like wikitext input.
--- Uses lookup table, instead of if-elseif-else statement, for efficiency.
--
-- If your wiki uses non-ASCII characters for any of "yes", "no", etc., you
-- should replace "string.lower" with "mw.ustring.lower" in the
-- following line. NOTE: It is _much_ slower.
local LOWER = string.lower
local TO_NUMBER = tonumber
local TYPE = type
local BOOLEAN_MAP = {
    yes = true, y = true, ['true'] = true, t = true, on = true, ['1'] = true,
    no = false, n = false, ['false'] = false, f = false, off = false, ['0'] = false
}
return function (value, defaultResponse)
    if value == nil then
        return nil
    end

    local valueType = TYPE(value)

    if valueType == 'boolean' then
        return value
    elseif valueType == 'string' then
        local lookupResult = BOOLEAN_MAP[LOWER(value)]
        if lookupResult ~= nil then
            return lookupResult
        end
    end

    -- Numeric check works for both numbers and numeric strings.
    local number = TO_NUMBER(value)
    if number == 1 then
        return true
    elseif number == 0 then
        return false
    end

    return defaultResponse
end