Lua Interpreter In Lua

wiki

Here's is a Lua 5.1 interpreter (lua.c) reimplemented in Lua. The primary goal is to most faithfully reimplement the standard Lua 5.1 interpreter in pure Lua. The goal is a bit different from InteractiveLua, which also implements a Lua interpreter but has differences and extensions. The task here is also partly analogous to LuaCompilerInLua (the Lua compiler front-end, luac.c, partially reimplemented in Lua).

Possible applications

Here's some things this might be used for:

Provide a Lua interpreter for "alternative implementations" of Lua (see section under LuaAddons) that lack a full Lua interpreter. For example, it would avoid writing [lua.pir] for Lua under Parrot.
Allow modifications to the Lua interpreter to be done more easily and readily since the implementation is in Lua rather than C.

Status

WARNING: This is not completed but was quickly done just an experiment. Fix omissions/bugs and test if you want to use this in production. Particularly pay attention to error handling.

Source

-- lua.lua - Lua 5.1 interpreter (lua.c) reimplemented in Lua.

--

-- WARNING: This is not completed but was quickly done just an experiment.

-- Fix omissions/bugs and test if you want to use this in production.

-- Particularly pay attention to error handling.

--

-- (c) David Manura, 2008-08

-- Licensed under the same terms as Lua itself.

-- Based on lua.c from Lua 5.1.3.

-- Improvements by Shmuel Zeigerman.



-- Variables analogous to those in luaconf.h

local LUA_INIT = "LUA_INIT"

local LUA_PROGNAME = "lua"

local LUA_PROMPT   = "> "

local LUA_PROMPT2  = ">> "

local function LUA_QL(x) return "'" .. x .. "'" end



-- Variables analogous to those in lua.h

local LUA_RELEASE   = "Lua 5.1.3"

local LUA_COPYRIGHT = "Copyright (C) 1994-2008 Lua.org, PUC-Rio"





-- Note: don't allow user scripts to change implementation.

-- Check for globals with "cat lua.lua | luac -p -l - | grep ETGLOBAL"

local _G = _G

local assert = assert

local collectgarbage = collectgarbage

local loadfile = loadfile

local loadstring = loadstring

local pcall = pcall

local rawget = rawget

local select = select

local tostring = tostring

local type = type

local unpack = unpack

local xpcall = xpcall

local io_stderr = io.stderr

local io_stdout = io.stdout

local io_stdin = io.stdin

local string_format = string.format

local string_sub = string.sub

local os_getenv = os.getenv

local os_exit = os.exit





local progname = LUA_PROGNAME



-- Use external functions, if available

local lua_stdin_is_tty = function() return true end

local setsignal = function() end



local function print_usage()

  io_stderr:write(string_format(

  "usage: %s [options] [script [args]].\n" ..

  "Available options are:\n" ..

  "  -e stat  execute string " .. LUA_QL("stat") .. "\n" ..

  "  -l name  require library " .. LUA_QL("name") .. "\n" ..

  "  -i       enter interactive mode after executing " ..

              LUA_QL("script") .. "\n" ..

  "  -v       show version information\n" ..

  "  --       stop handling options\n" ..

  "  -        execute stdin and stop handling options\n"

  ,

  progname))

  io_stderr:flush()

end



local function l_message (pname, msg)

  if pname then io_stderr:write(string_format("%s: ", pname)) end

  io_stderr:write(string_format("%s\n", msg))

  io_stderr:flush()

end



local function report(status, msg)

  if not status and msg ~= nil then

    msg = (type(msg) == 'string' or type(msg) == 'number') and tostring(msg)

          or "(error object is not a string)"

    l_message(progname, msg);

  end

  return status

end



local function tuple(...)

  return {n=select('#', ...), ...}

end



local function traceback (message)

  local tp = type(message)

  if tp ~= "string" and tp ~= "number" then return message end

  local debug = _G.debug

  if type(debug) ~= "table" then return message end

  local tb = debug.traceback

  if type(tb) ~= "function" then return message end

  return tb(message, 2)

end



local function docall(f, ...)

  local tp = {...}  -- no need in tuple (string arguments only)

  local F = function() return f(unpack(tp)) end

  setsignal(true)

  local result = tuple(xpcall(F, traceback))

  setsignal(false)

  -- force a complete garbage collection in case of errors

  if not result[1] then collectgarbage("collect") end

  return unpack(result, 1, result.n)

end



local function dofile(name)

  local f, msg = loadfile(name)

  if f then f, msg = docall(f) end

  return report(f, msg)

end



local function dostring(s, name)

  local f, msg = loadstring(s, name)

  if f then f, msg = docall(f) end

  return report(f, msg)

end



local function dolibrary (name)

  return report(docall(_G.require, name))

end



local function print_version()

  l_message(nil, LUA_RELEASE .. "  " .. LUA_COPYRIGHT)

end



local function getargs (argv, n)

  local arg = {}

  for i=1,#argv do arg[i - n] = argv[i] end

  if _G.arg then

    local i = 0

    while _G.arg[i] do

      arg[i - n] = _G.arg[i]

      i = i - 1

    end

  end

  return arg

end



--FIX? readline support

local history = {}

local function saveline(s)

--  if #s > 0 then

--    history[#history+1] = s

--  end

end





local function get_prompt (firstline)

  -- use rawget to play fine with require 'strict'

  local pmt = rawget(_G, firstline and "_PROMPT" or "_PROMPT2")

  local tp = type(pmt)

  if tp == "string" or tp == "number" then

    return tostring(pmt)

  end

  return firstline and LUA_PROMPT or LUA_PROMPT2

end





local function incomplete (msg)

  if msg then

    local ender = LUA_QL("<eof>")

    if string_sub(msg, -#ender) == ender then

      return true

    end

  end

  return false

end





local function pushline (firstline)

  local prmt = get_prompt(firstline)

  io_stdout:write(prmt)

  io_stdout:flush()

  local b = io_stdin:read'*l'

  if not b then return end -- no input

  if firstline and string_sub(b, 1, 1) == '=' then

    return "return " .. string_sub(b, 2)  -- change '=' to `return'

  else

    return b

  end

end





local function loadline ()

  local b = pushline(true)

  if not b then return -1 end  -- no input

  local f, msg

  while true do  -- repeat until gets a complete line

    f, msg = loadstring(b, "=stdin")

    if not incomplete(msg) then break end  -- cannot try to add lines?

    local b2 = pushline(false)

    if not b2 then -- no more input?

      return -1

    end

    b = b .. "\n" .. b2 -- join them

  end



  saveline(b)



  return f, msg

end





local function dotty ()

  local oldprogname = progname

  progname = nil

  while true do

    local result

    local status, msg = loadline()

    if status == -1 then break end

    if status then

      result = tuple(docall(status))

      status, msg = result[1], result[2]

    end

    report(status, msg)

    if status and result.n > 1 then  -- any result to print?

      status, msg = pcall(_G.print, unpack(result, 2, result.n))

      if not status then

        l_message(progname, string_format(

            "error calling %s (%s)",

            LUA_QL("print"), msg))

      end

    end

  end

  io_stdout:write"\n"

  io_stdout:flush()

  progname = oldprogname

end





local function handle_script(argv, n)

  _G.arg = getargs(argv, n)  -- collect arguments

  local fname = argv[n]

  if fname == "-" and argv[n-1] ~= "--" then

    fname = nil  -- stdin

  end

  local status, msg = loadfile(fname)

  if status then

    status, msg = docall(status, unpack(_G.arg))

  end

  return report(status, msg)

end





local function collectargs (argv, p)

  local i = 1

  while i <= #argv do

    if string_sub(argv[i], 1, 1) ~= '-' then  -- not an option?

      return i

    end

    local prefix = string_sub(argv[i], 1, 2)

    if prefix == '--' then

      if #argv[i] > 2 then return -1 end

      return argv[i+1] and i+1 or 0

    elseif prefix == '-' then

      return i

    elseif prefix == '-i' then

      if #argv[i] > 2 then return -1 end

      p.i = true

      p.v = true

    elseif prefix == '-v' then

      if #argv[i] > 2 then return -1 end

      p.v = true

    elseif prefix == '-e' then

      p.e = true

      if #argv[i] == 2 then

        i = i + 1

        if argv[i] == nil then return -1 end

      end

    elseif prefix == '-l' then

      if #argv[i] == 2 then

        i = i + 1

        if argv[i] == nil then return -1 end

      end

    else

      return -1  -- invalid option

    end

    i = i + 1

  end

  return 0

end





local function runargs(argv, n)

  local i = 1

  while i <= n do if argv[i] then

    assert(string_sub(argv[i], 1, 1) == '-')

    local c = string_sub(argv[i], 2, 2) -- option

    if c == 'e' then

      local chunk = string_sub(argv[i], 3)

      if chunk == '' then i = i + 1; chunk = argv[i] end

      assert(chunk)

      if not dostring(chunk, "=(command line)") then return false end

    elseif c == 'l' then

      local filename = string_sub(argv[i], 3)

      if filename == '' then i = i + 1; filename = argv[i] end

      assert(filename)

      if not dolibrary(filename) then return false end

    end

    i = i + 1

  end end

  return true

end





local function handle_luainit()

  local init = os_getenv(LUA_INIT)

  if init == nil then

    return  -- status OK

  elseif string_sub(init, 1, 1) == '@' then

    dofile(string_sub(init, 2))

  else

    dostring(init, "=" .. LUA_INIT)

  end

end





local import = _G.import

if import then

  lua_stdin_is_tty = import.lua_stdin_is_tty or lua_stdin_is_tty

  setsignal        = import.setsignal or setsignal

  LUA_RELEASE      = import.LUA_RELEASE or LUA_RELEASE

  LUA_COPYRIGHT    = import.LUA_COPYRIGHT or LUA_COPYRIGHT

  _G.import = nil

end



if _G.arg and _G.arg[0] and #_G.arg[0] > 0 then progname = _G.arg[0] end

local argv = {...}

handle_luainit()

local has = {i=false, v=false, e=false}

local script = collectargs(argv, has)

if script < 0 then -- invalid args?

  print_usage()

  os_exit(1)

end

if has.v then print_version() end

local status = runargs(argv, (script > 0) and script-1 or #argv)

if not status then os_exit(1) end

if script ~= 0 then

  status = handle_script(argv, script)

  if not status then os_exit(1) end

else

  _G.arg = nil

end

if has.i then

  dotty()

elseif script == 0 and not has.e and not has.v then

  if lua_stdin_is_tty() then

    print_version()

    dotty()

  else dofile(nil)  -- executes stdin as a file

  end

end

Lua Interpreter In Lua

Possible applications

Status

Source

See Also