Simple Lua Preprocessor

wiki

function prep(file)

  local chunk = {n=0}

  for line in file:lines() do

     if string.find(line, "^#") then

      table.insert(chunk, string.sub(line, 2) .. "\n")

     else

      local last = 1

      for text, expr, index in string.gmatch(line, "(.-)$(%b())()") do 

        last = index

        if text ~= "" then

          table.insert(chunk, string.format('io.write %q ', text))

        end

        table.insert(chunk, string.format('io.write%s ', expr))

      end

      table.insert(chunk, string.format('io.write %q\n',

                                         string.sub(line, last).."\n"))

    end

  end

  return loadstring(table.concat(chunk))()

end

Lines starting with # are executed as Lua. Other lines are sent through as is, except that $(...) appearing anywhere in them is executed. (No parsing is done, so you have to be careful with your $('s)

Sample input:

#if DEBUG then

  function log(fmt, ...) print(string.format(fmt, unpack(arg))) end

#else

  function log() end

#end



#for i = 0, 10 do

  var$(i) = $(math.sin(math.pi * i / 10))

#end

Sample output:

> prep(assert(io.open"sample.luap"))

  function log() end



  var0 = 0

  var1 = 0.30901699437495

  var2 = 0.58778525229247

  var3 = 0.80901699437495

  var4 = 0.95105651629515

  var5 = 1

  var6 = 0.95105651629515

  var7 = 0.80901699437495

  var8 = 0.58778525229247

  var9 = 0.30901699437495

  var10 = 1.2246467991474e-16







> DEBUG = true

> prep(assert(io.open"sample.luap"))

  function log(fmt, ...) print(string.format(fmt, unpack(arg))) end



  var0 = 0

  var1 = 0.30901699437495

  var2 = 0.58778525229247

  var3 = 0.80901699437495

  var4 = 0.95105651629515

  var5 = 1

  var6 = 0.95105651629515

  var7 = 0.80901699437495

  var8 = 0.58778525229247

  var9 = 0.30901699437495

  var10 = 1.2246467991474e-16