lua table dumping as pseudo-yaml

_G.yml

__root: &__root_t0x4004f960
 _G: *__root_t0x4004f960
 _VERSION: Lua 5.1
 arg: &arg_t0x40055cc8
  "-1": luajit
  0: run.lua
 assert: fbuiltin#2
 bit: &bit_t0x40054d58
  arshift: fbuiltin#70
  band: fbuiltin#73
  bnot: fbuiltin#66
  bor: fbuiltin#74
  bswap: fbuiltin#67
  bxor: fbuiltin#75
  lshift: fbuiltin#68
  rol: fbuiltin#71
  ror: fbuiltin#72
  rshift: fbuiltin#69
  tobit: fbuiltin#65
  tohex: fbuiltin#76
 collectgarbage: fbuiltin#27
 coroutine: &coroutine_t0x40051730
  create: fbuiltin#32
  resume: fbuiltin#34
  running: fbuiltin#31
  status: fbuiltin#30
  wrap: fbuiltin#36
  yield: fbuiltin#33
 debug: &debug_t0x40054740
  debug: fbuiltin#145
  getfenv: fbuiltin#134
  gethook: fbuiltin#144
  getinfo: fbuiltin#136
  getlocal: fbuiltin#137
  getmetatable: fbuiltin#132
  getregistry: fbuiltin#131
  getupvalue: fbuiltin#139
  setfenv: fbuiltin#135
  sethook: fbuiltin#143
  setlocal: fbuiltin#138
  setmetatable: fbuiltin#133
  setupvalue: fbuiltin#140
  traceback: fbuiltin#146
  upvalueid: fbuiltin#141
  upvaluejoin: fbuiltin#142
 dofile: fbuiltin#25
 dump: f0x4005dd40
 error: fbuiltin#19
 gcinfo: fbuiltin#26
 getfenv: fbuiltin#10
 getmetatable: fbuiltin#8
 io: &io_t0x40052a90
  close: fbuiltin#112
  flush: fbuiltin#115
  input: fbuiltin#116
  lines: fbuiltin#118
  open: fbuiltin#109
  output: fbuiltin#117
  popen: fbuiltin#110
  read: fbuiltin#113
  stderr: file (0x7ff9dd21f500)
  stdin: file (0x7ff9dd21e8a0)
  stdout: file (0x7ff9dd21f5e0)
  tmpfile: fbuiltin#111
  type: fbuiltin#119
  write: fbuiltin#114
 ipairs: fbuiltin#7
 jit: &jit_t0x40055318
  arch: x64
  attach: fbuiltin#151
  flush: fbuiltin#149
  off: fbuiltin#148
  on: fbuiltin#147
  opt: &opt_t0x40055bd8
   start: fbuiltin#163
  os: Linux
  status: fbuiltin#150
  util: &util_t0x400556a0
   funcbc: fbuiltin#153
   funcinfo: fbuiltin#152
   funck: fbuiltin#154
   funcuvname: fbuiltin#155
   ircalladdr: fbuiltin#162
   traceexitstub: fbuiltin#161
   traceinfo: fbuiltin#156
   traceir: fbuiltin#157
   tracek: fbuiltin#158
   tracemc: fbuiltin#160
   tracesnap: fbuiltin#159
  version: LuaJIT 2.0.4
  version_num: 20004
 load: fbuiltin#23
 loadfile: fbuiltin#22
 loadstring: fbuiltin#24
 math: &math_t0x40053b60
  abs: fbuiltin#37
  acos: fbuiltin#47
  asin: fbuiltin#46
  atan: fbuiltin#48
  atan2: fbuiltin#57
  ceil: fbuiltin#39
  cos: fbuiltin#44
  cosh: fbuiltin#50
  deg: fbuiltin#54
  exp: fbuiltin#42
  floor: fbuiltin#38
  fmod: fbuiltin#59
  frexp: fbuiltin#52
  huge: inf
  ldexp: fbuiltin#60
  log: fbuiltin#56
  log10: fbuiltin#41
  max: fbuiltin#62
  min: fbuiltin#61
  mod: fbuiltin#59
  modf: fbuiltin#53
  pi: 3.1415926535898
  pow: fbuiltin#58
  rad: fbuiltin#55
  random: fbuiltin#63
  randomseed: fbuiltin#64
  sin: fbuiltin#43
  sinh: fbuiltin#49
  sqrt: fbuiltin#40
  tan: fbuiltin#45
  tanh: fbuiltin#51
 module: f0x40051ee0
 newproxy: fbuiltin#28
 next: fbuiltin#4
 os: &os_t0x40052fd0
  clock: fbuiltin#126
  date: fbuiltin#127
  difftime: fbuiltin#129
  execute: fbuiltin#120
  exit: fbuiltin#125
  getenv: fbuiltin#124
  remove: fbuiltin#121
  rename: fbuiltin#122
  setlocale: fbuiltin#130
  time: fbuiltin#128
  tmpname: fbuiltin#123
 package: &package_t0x40051ac8
  config: 
   /
   ;
   ?
   !
   -
  cpath: /home/notwa/opt/local/lib/?.so;/home/notwa/.luarocks/lib/lua/5.1/?.so;/home/notwa/opt/local/lib/lua/5.1/?.so;./?.so;/usr/local/lib/lua/5.1/?.so;/usr/local/lib/lua/5.1/loadall.so
  loaded: &loaded_t0x40050b38
   _G: *__root_t0x4004f960
   bit: *bit_t0x40054d58
   coroutine: *coroutine_t0x40051730
   debug: *debug_t0x40054740
   extra: &extra_t0x4005cd30
    add_zeros: f0x4005db58
    mixed_sorter: f0x4005db98
    opairs: f0x4005cca8
    order_keys: f0x4005b2f8
    strpad: f0x4004f8b8
    traverse: f0x4005cce8
   io: *io_t0x40052a90
   jit: *jit_t0x40055318
   "jit.opt": *opt_t0x40055bd8
   "jit.util": *util_t0x400556a0
   math: *math_t0x40053b60
   os: *os_t0x40052fd0
   package: *package_t0x40051ac8
   pt: &pt_t0x4005ce20
    __metatable: *pt_t0x4005ce20
    __call: f0x4005dc98
    __index: *pt_t0x4005ce20
    inner: f0x4005dde0
    outer: f0x4005dd18
    outer_old: f0x4005dc00
    safecanon: f0x4005dd60
    safekey: f0x4005dd80
    safeval: f0x4005ddc0
    write: f0x4005dcd8
   string: *string_t0x400534b0
   table: *table_t0x400522f8
  loaders: &loaders_t0x40051c38
   1: f0x40051c88
   2: f0x40051cb0
   3: f0x40051cd8
   4: f0x40051d00
  loadlib: f0x40051b58
  path: /home/notwa/.luarocks/share/lua/5.1/?.lua;/home/notwa/.luarocks/share/lua/5.1/?/init.lua;/home/notwa/opt/local/share/lua/5.1/?.lua;/home/notwa/opt/local/share/lua/5.1/?/init.lua;./?.lua;/home/notwa/opt/local/share/luajit-2.1.0-beta1/?.lua;/usr/local/share/lua/5.1/?.lua;/usr/local/share/lua/5.1/?/init.lua
  preload: &preload_t0x400520c0
   ffi: f0x40055c80
  searchpath: f0x40051ba0
  seeall: f0x40051bf0
 pairs: fbuiltin#5
 pcall: fbuiltin#20
 print: fbuiltin#29
 rawequal: fbuiltin#14
 rawget: fbuiltin#12
 rawset: fbuiltin#13
 require: f0x40051f28
 select: fbuiltin#16
 setfenv: fbuiltin#11
 setmetatable: fbuiltin#9
 string: &string_t0x400534b0
  byte: fbuiltin#78
  char: fbuiltin#79
  dump: fbuiltin#85
  find: fbuiltin#86
  format: fbuiltin#91
  gfind: fbuiltin#89
  gmatch: fbuiltin#89
  gsub: fbuiltin#90
  len: fbuiltin#77
  lower: fbuiltin#83
  match: fbuiltin#87
  rep: fbuiltin#81
  reverse: fbuiltin#82
  sub: fbuiltin#80
  upper: fbuiltin#84
 t: &t_t0x4005e298
  A: hello
  B: &B_t0x4005e328
   a: beep
   b: boop
   c: burp
   d: *d_t0x4005e550
  C: &d_t0x4005e550
   a: nude
   b: dude
   c: lewd
   d: *B_t0x4005e328
  D: goodbye
  E: *t_t0x4005e298
 table: &table_t0x400522f8
  concat: fbuiltin#98
  foreach: fbuiltin#93
  foreachi: fbuiltin#92
  getn: fbuiltin#94
  insert: fbuiltin#96
  maxn: fbuiltin#95
  remove: fbuiltin#97
  sort: fbuiltin#99
 tonumber: fbuiltin#17
 tostring: fbuiltin#18
 type: fbuiltin#3
 unpack: fbuiltin#15
 xpcall: fbuiltin#21

extra.lua

local insert = table.insert
local pairs = pairs
local rawget = rawget
local sort = table.sort
local tostring = tostring
local type = type

local function strpad(num, count, pad)
    num = tostring(num)
    return (pad:rep(count)..num):sub(#num)
end

local function add_zeros(num, count)
    return strpad(num, count - 1, '0')
end

local function mixed_sorter(a, b)
    a = type(a) == 'number' and add_zeros(a, 16) or tostring(a)
    b = type(b) == 'number' and add_zeros(b, 16) or tostring(b)
    return a < b
end

-- loosely based on http://lua-users.org/wiki/SortedIteration
-- the original didn't make use of closures for who knows why
local function order_keys(t)
    local oi = {}
    for key in pairs(t) do
        insert(oi, key)
    end
    sort(oi, mixed_sorter)
    return oi
end

local function opairs(t, cache)
    local oi = cache and cache[t] or order_keys(t)
    if cache then
        cache[t] = oi
    end
    local i = 0
    return function()
        i = i + 1
        local key = oi[i]
        if key ~= nil then return key, t[key] end
    end
end

local function traverse(path)
    if not path then return end
    local parent = _G
    local key
    for w in path:gfind("[%w_]+") do
        if key then
            parent = rawget(parent, key)
            if type(parent) ~= 'table' then return end
        end
        key = w
    end
    if not key then return end
    return {parent=parent, key=key}
end

return {
    strpad = strpad,
    add_zeros = add_zeros,
    mixed_sorter = mixed_sorter,
    order_keys = order_keys,
    opairs = opairs,
    traverse = traverse,
}

init.lua

local path = string.gsub(..., "[^.]+$", "")
return require(path.."pt")

pt.lua

local path = string.gsub(..., "[^.]+$", "")
local extra = require(path.."extra")
local opairs = extra.opairs

local pt = {}
pt.__index = pt
setmetatable(pt, pt)

local function rawstr(v)
    if v == nil then return 'nil' end
    local mt = getmetatable(v)
    local ts = mt and rawget(mt, '__tostring')
    if not ts then return tostring(v) end
    mt.__tostring = nil
    local s = tostring(v)
    mt.__tostring = ts
    return s
end

local function getaddr(t)
    return rawstr(t):sub(#type(t) + 3)
end

local function copy(t)
    -- shallow copy
    if type(t) ~= 'table' then return end
    local new = {}
    for k,v in pairs(t) do
        new[k] = v
    end
    return new
end

function pt.__call(pt, args)
    -- print a table as semi-valid YAML
    -- with references to prevent recursion/duplication
    local t = args.table or args[1]
    local self = {}
    setmetatable(self, pt)
    self.seen = copy(args.seen) or {}
    self.skipped = copy(args.skipped) or {}
    self.seen_elsewhere = args.seen or {}
    self.depth = args.depth or 16
    self.writer = args.writer or io.write
    self.skeleton = args.skeleton or false
    self.outer = args.alt_order and self.outer_old or self.outer
    self.noncanon = args.noncanon or false
    self.indent = args.indent or ' '
    self.queued = {}
    self.cache = {}
    self.canonicalized = {}
    self:inner('__root', t, '')
    return self.seen
end

function pt:write(...)
    self.writer(...)
end

function pt:safecanon(k)
    local s = tostring(k)
    return s:gsub('[^%w_]', '_')
end

function pt:safekey(k)
    if type(k) == 'table' then
        return 't'..getaddr(k)
    end
    local s = tostring(k)
    s = s:gsub('[\r\n]', '')
    return s:find('[^%w_]') and ('%q'):format(s) or s
end

function pt:safeval(v, indentation)
    if type(v) == 'function' then
        return 'f'..getaddr(v)
    end
    local s = tostring(v)
    if type(v) == 'number' then
        return s
    end
    -- TODO: move newline/indentation handling to another function?
    if s:find('[\r\n]') then
        s = ('\n'..s):gsub('[\r\n]', '\n'..indentation..self.indent)
    end
    --local safe = ('%q'):format(s)
    --return s == safe:sub(2, -2) and s or safe
    -- TODO: finish matching valid characters
    return s:find('[^%w_()[]{}.]') and ('%q'):format(s) or s
end

function pt:inner(k, v, indentation)
    if type(v) ~= 'table' then
        if self.skeleton then return end
        self:write(indentation, self:safekey(k), ': ')
        self:write(self:safeval(v, indentation), '\n')
        return
    end

    local addr = getaddr(v)
    self:write(indentation, self:safekey(k))

    local canon
    if not self.noncanon and type(k) ~= 'table' then
        canon = self.canonicalized[addr]
        if canon == nil then
            canon = self:safecanon(k)..'_t'..addr
            self.canonicalized[addr] = canon
        end
    else
        canon = 't'..addr
    end

    if #indentation > self.depth or self.skipped[addr] then
        --self.skipped[addr] = true -- TODO: extra logics
        self:write(': #', canon, '\n')
        return
    end

    if self.seen[addr] or self.queued[addr] then
        self:write(': *', canon, self.seen_elsewhere[addr] and ' #\n' or '\n')
        return
    end

    self.seen[addr] = true

    self:write(': &', canon, '\n')
    self:outer(v, indentation..self.indent)
end

function pt:outer_old(t, indentation)
    if type(t) ~= "table" then
        local s = self:safeval(t, indentation)
        self:write(indentation, s, '\n')
        return
    end

    local ours = {}
    local not_ours = {}

    for k,v in opairs(t) do
        if type(v) == 'table' then
            local addr = getaddr(v)
            if not (self.queued[addr] or self.seen[addr] or self.skipped[addr]) then
                self.queued[addr] = true
                ours[k] = v
            else
                not_ours[k] = v
            end
        else
            self:inner(k, v, indentation)
        end
    end

    for k,v in opairs(not_ours) do
        self:inner(k, v, indentation)
    end

    for k,v in opairs(ours) do
        self.queued[getaddr(v)] = nil
        self:inner(k, v, indentation)
    end

    local mt = getmetatable(t)
    if mt ~= nil then
        self:inner('__metatable', mt, indentation)
    end
end

function pt:outer(t, indentation)
    if type(t) ~= "table" then
        local s = self:safeval(t, indentation)
        self:write(indentation, s, '\n')
        return
    end

    local ours = {}

    for k,v in opairs(t, self.cache) do
        if type(v) == 'table' then
            local addr = getaddr(v)
            if not (self.queued[addr] or self.seen[addr] or self.skipped[addr]) then
                self.queued[addr] = true
                ours[k] = addr
            end
        end
    end

    local mt = getmetatable(t)
    if mt ~= nil then
        self:inner('__metatable', mt, indentation)
    end

    for k,v in opairs(t, self.cache) do
        local addr = ours[k]
        if addr then
            self.queued[addr] = nil
        end
        self:inner(k, v, indentation)
    end
end

return pt

run.lua

#!/usr/bin/lua
local pt = require('pt')

t = {
    A = 'hello',
    B = {
        a = 'beep',
        b = 'boop',
        c = 'burp',
    },
    C = {
        a = 'nude',
        b = 'dude',
        c = 'lewd',
    },
    D = 'goodbye',
}
t.B.d = t.C
t.C.d = t.B
t.E = t

function dump(t, fn, seen)
    if t == nil then return end

    local file = io.open(fn, "w")
    if not file then
        io.write("Failed opening ", fn, "\n")
        return
    end

    local writer = function(...)
        file:write(...)
    end
    seen = pt{t, writer=writer, seen=seen}

    file:close()
    return seen
end

pt{t}
dump(_G, '_G.yml')