permutation_case_lua

local concat, insert, unpack = table.concat, table.insert, table.unpack
function permutecase(word)
  local ret = {}
  for i = #word, 1, -1 do
    if i == #word then
      ret[#ret+1] = word:sub(i,i):lower()
      ret[#ret+1] = word:sub(i,i):upper()
    else
      for j = 1, #ret do
        local case = ret[j]
        ret[#ret+1] = word:sub(i,i):upper() .. ret[j]
        ret[j] = word:sub(i,i):lower() .. ret[j]
      end
    end
  end
  return ret
end

for i, v in ipairs(permutecase("pass")) do
  print(i, v)
end