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
oder 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 (eg. Yes
) always return true
, and some (eg. No
) always return false
. nil
values always return nil
.
-- 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)
-- Nil values always return 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') -- Because string "foo" doesn't a truth value, so the yesno function return nil.
-- "Sí" in Breton language or "いいえ" in Japanese will return nil.
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.
Code
local p = {}
function p.yesno(frame)
-- defaults
local retvals = {
yes = "yes",
no = "",
["¬"] = ""
}
-- Allow arguments to override defaults.
-- 'any' tracks the presence of any arguments at all.
local args = frame.args
local any = false
for k,v in pairs(args) do
any = true
retvals[k] = v
end
-- If there are no arguments, try and get them from the parent frame.
if any == false then
local pframe = frame:getParent()
args = pframe.args
for k,v in pairs(args) do
any = true
retvals[k] = v
end
end
val = args[1]
-- First deal with the case if val is nil, then deal with other cases.
if val == nil then
return retvals['¬']
end
val = val:lower() -- Coerce to blank if nil; make lowercase.
val = val:match'^%s*(.*%S)' or '' -- Trim whitespace.
if val == '' then
return retvals['blank'] or retvals['no']
elseif val == 'n' or val == 'no' or val == '0' then
return retvals['no']
elseif val == 'y' or val == 'yes' or val == '1' or retvals['def'] == nil then
return retvals['yes']
else
return retvals['def']
end
end
return p