Module:Yesno

local p = {}

function p.yesno(frame)

   -- defaults
   local retvals = {
       yes   = "yes",
       no    = "",
       ["¬"] = ""
   }

   -- Allow arguments to override defaults. Arguments are taken from
   -- the parent frame; other arguments are ignored.
   for k,v in pairs(frame.args) do
       retvals[k] = v
   end

   val = frame.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()          -- Make lowercase.
   val = val:match'^%s*(.*%S)' or   -- Trim whitespace.

   -- Cases are ordered by (probable) likelihood of use. 
   if val ==  then
       return retvals['blank'] or retvals['no']
   elseif val == 'yes' then
       return retvals['yes']
   elseif val == 'no' then
       return retvals['no']
   elseif val == 'y' then
       return retvals['yes']
   elseif val == 'n' then
       return retvals['no']
   elseif val == '¬' then
       return retvals['¬']
   elseif tonumber(val) == 1 then
       return retvals['yes']
   elseif tonumber(val) == 0 then
       return retvals['no']
   else
       return retvals['def'] or retvals['yes']
   end

end

return p