exercises.lua

function dirtree(dir)

  if string.sub(dir, -1) == "/" then
    dir=string.sub(dir, 1, -2)
  end

  local function yieldtree(dir)
    for entry in lfs.dir(dir) do
      if not entry:match("^%.") then
        entry=dir.."/"..entry
          if lfs.isdir(entry) then
            yieldtree(entry)
          else
            coroutine.yield(entry)
          end
      end
    end
  end

  return coroutine.wrap(function() yieldtree(dir) end)
end

--- Check if a file or directory exists in this path
function exists(file)
   local ok, err, code = os.rename(file, file)
   if not ok then
      if code == 13 then
         -- Permission denied, but it exists
         return true
      end
   end
   return ok, err
end

--- Check if a directory exists in this path
function isdir(path)
   -- "/" works on both Unix and Windows
   return exists(path.."/")
end

local dirname = status.filename:gsub(".tex$","")

filenames = {}

if isdir(dirname) then
  for i in dirtree(dirname) do
     local filename = i:gsub(".*/([^/]+)$","%1")
     if filename:match(".tex$") then
       table.insert( filenames, filename )
     end
  end

  table.sort(filenames)

  for i, v in pairs(filenames) do
    tex.sprint("\\subfile{" ..  dirname .. "/" .. v .. "}")
  end
end