# Pretty #

## Introduction

`pretty` is an advanced pretty printer for [Lua](lua.org) aiming primarily for
human readability. It does this by looking for patterns in the input data, and
creating an output string utilizing and highlighting those patterns. Thus it's
a primarily a debugging tool, not a speedy serialization tool.

This project is the outcome of my frustration with existing pretty printers, and
a desire to expand upon the pretty printer I developed for
[Xenoterm](https://gitfub.space/takunomi/Xenoterm). The default Xenoterm pretty
printer is much simpler than `pretty`, but the enhancements compared to other
pretty printers, inspired me to create `pretty`. See the bottom of the page for
other pretty printers.

`pretty` sorts it's priorities like so:

1.	Human readability.
2.	Lua-compatible output.
3.	Customization.

I'd rather have good defaults than provide a ton of customization options. And
if some structure cannot be represented in Lua, I will rather extend the
syntax, than lose the info.

Another aspect where `pretty` shines is in exploratory programming, when
attempting to avoid reliance on outside documentation. The amount of information
`pretty` exposes varies by the data you are inspecting. If you're inspecting
a list of functions, their function signatures are visible, but if you're
inspecting a single function, documentation and source location may appear if
available.

## Features

-	Written in good-old pureblood Lua, with support for PUC Lua 5.0+ and
	LuaJIT 2.0+.
-	Redefining what it means to be "human readable":
	*	Is multi-line centric, to aid readablitiy.
	*	Indention and alignment of keys-value pairs.
	*	Keys-value pairs are [properly](http://www.davekoelle.com/alphanum.html)
		sorted by key type and thereafter alphabetically.
	*	The format and structure of output changes depending upon the input.
		Maps appear differently to deeply nested tables to long sequences
		with short strings to short lists.
	*	Uses the standard `debug` library to gain information about functions
		and other advanced structures.

## Readability Methods

Here we outline the methods we use when formatting.

The simplest method is to align keys, equals-sign and values, of a table. Thus
we separate them, and make it easier to distinguish them from each. Compare:

```lua
	bad = {
		a = 'hello world',
		hello = 'hi'
	}
	good = {
		a      =  'hello world',
		hello  =  'hi'
	}
```

## Performance

As specified in the introduction, `pretty` is not a performance oriented
library. Expected usage is in error conditions and debugging, not in tight
inner loops.

Don't use `pretty.lua` if you want fast serialization. Use one of the pretty
printers specified below.

## TODO

I'm looking into implementing following features:

-	Improve display of medium-long lists with short elements. One option is
	something analog to the default results of `ls` on Linux.
-	Add support for `setmetatable`, and exploring the values accessible through
	it.
-	Provide nice formatting for `cdata` datatype in LuaJIT.
-	Expand on the comment output in output, for `__tostring` methods, and global
	namespaces like `io` or `math`.
-	Look into using concat operation to improve appearance of overly long
	non-breaking strings. Attempt to break near whitespace.
-	Attempt to fit output within a predefined width limit. Default to 80.
-	Find a better name than `pretty`.
-	Add options for colored output, and allow custom formatting.
-	Look more into `string.dump` in the core library.
-	Better support upvalues for in functions. Complete support is impossible
	without traversing the original code or inspecting the intermediate
	representation, due to lexical scoping. (Pluto does it, but it's written in
	C.)

## Other pretty printers

`pretty` is a large and slow library, and is not designed for serialization
purposes, nor is `pretty` concerned with offering the same level of
customization as other libraries do.

Luckily Lua has a large library of pretty printers and serialization libraries:

-	[inspect.lua](github.com/kikito/inspect.lua): One of the classic debugging
	pretty printers.
-	[pprint.lua](github.com/jagt/pprint.lua): Reimplementation of `inspect.lua`
-	[serpent](github.com/pkulchenko/serpent): Advanced and fast pretty printer.
-	[pluto](lua-users.org/wiki/PlutoLibrary): Can serialize arbitrary parts of
	Lua, including functions, upvalues, and proper lexical scoping. Not written
	in native Lua.
-	[binser](github.com/bakpakin/binser): Library for special purpose
	serialization.

Others can be found at [the lua-users wiki](lua-users.org/wiki/TableSerialization).