table serialization

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local pp = require'pp'

Fast, compact serialization producing portable Lua source code.


  • all Lua types except coroutines, userdata, cdata and C functions.
  • the ffi int64_t and uint64_t types.
  • values featuring the __pwrite metamethod.


  • compact: no spaces, dot notation for identifier keys, minimal quoting of strings, implicit keys for the array part of tables.
  • portable between LuaJIT 2, Lua 5.1, Lua 5.2: dot key notation only for ascii identifiers, numbers are in decimal, NaN and ┬▒Inf are written as 0/0, 1/0 and -1/0 respectively.
  • portable between Windows, Linux, Mac: quoting of \n and \r protects binary integrity when opening in text mode.
  • embeddable: can be copy-pasted into Lua source code: quoting of \0 and \t protects binary integrity with code editors.
  • human readable: indentation (optional, configurable); array part printed separately with implicit keys.
  • stream-based: the string bits are written with a writer function to minimize the amount of string concatenation and memory footprint.
  • non-deterministic: table keys are not sorted, so not friendly to diff or checksum.
  • non-identical: object identity is not tracked and is not preserved (table references are dereferenced).


  • recursive: table nesting depth is stack-bound.
  • some fractions are not compact eg. the fraction 5/6 takes 19 bytes vs 8 bytes in its native double format.
  • strings need escaping which could become noticeable with large strings featuring many newlines, tabs, zero bytes, apostrophes, backslashes or control characters.
  • loading back the output with the Lua interpreter is not safe (no code is).


pp(v1, ...)

Pretty-print the arguments to standard output. Cycle detection and indentation are enabled. Unserializable values get a comment in place.

pp.write(write, v, [, indent][, parents][, quote][, onerror])

Pretty-print a value using a supplied write function that takes a string. The other arguments are:

  • indent - enable indentation eg. '\t' indents by one tab (default is compact output with no whitespace)
  • parents - enable cycle detection eg. {}
  • quote - change string quoting eg. '"' (default is "'")
  • onerror - enable error handling eg. function(err_type, v, depth) error(err_type..': '..tostring(v)) end


local function chunks(t)
   return coroutine.wrap(function()
      return pp.write(coroutine.yield, t)

for s in chunks(t) do

pp.save(file, v[, indent][, parents][, quote][, onerror])

Pretty-print a value to a file.

pp.format(v[, indent][, parents][, quote][, onerror]) -> s

Pretty-print a value to a string.