pretty/README.md

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# Pretty

[pretty](index.html#) is an advanced pretty printer for [Lua](https://lua.org).

 It's primarily a
debugging tool, aiming for human readability, by detecting pattern in the input
data, and creating an output string utilizing and highlighting those patterns.

## Code Example

Setup is simple, use `pretty = require 'pretty'`, and you're good to go.

```
$ print(pretty( { 1, 2, 3 } ))
{ 1, 2, 3 }

$ print(pretty( { hello = 'world', num = 42 } ))
{
    num   = 42
    hello = 'world'
}

$ print(pretty( { abs = math.abs, max = math.max, some = function() end } ))
{
    abs  = builtin function (x)      ... end
    max  = builtin function (x, ...) ... end
    some =         function ()       ... end
}

$ print(pretty( math.abs ))
builtin function (x)
    -- math.abs
    -- Returns the absolute value of x

    ...
end
```

## Motivation

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 original Xenoterm pretty
printer was much simpler than [pretty](index.html#) - and the current is even simpler - but
the enhancements I make, when compared to other pretty printers, inspired me to
create [pretty](index.html#).

[pretty](index.html#) sorts it's priorities like so:

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

I'd rather have good defaults than provide a ton of customization options. If an
structure avoids easy representation in Lua, I'd rather extend the syntax, than
lose the info.

Another aspect where [pretty](index.html#) shines is in exploratory programming, when
attempting to avoid reliance on outside documentation. The amount of information
[pretty](index.html#) 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 pure-blood 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 readability.
- Indention and alignment of keys-value pairs.
- Keys-value pairs are
    [alpha-numerically](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](https://www.lua.org/manual/5.1/manual.html#5.9) library to gain information about functions and
    other advanced structures.

## Installation

[pretty](index.html#) is loadable directly with [require](https://www.lua.org/manual/5.1/manual.html#pdf-require). Either clone or download this
repository. Where you place it, depends upon what you want to do:

1. **You want [pretty](index.html#) in a specific project**: Place the [pretty](index.html#) folder
    somewhere in your project, and [require](https://www.lua.org/manual/5.1/manual.html#pdf-require) it from one of your project files.
1. **You want [pretty](index.html#) on your system**: Place the [pretty](index.html#) folder such that
    it's visible from your Lua-path. On my system this might be
    `/usr/local/share/lua/5.1/`. Now you can [require](https://www.lua.org/manual/5.1/manual.html#pdf-require) it from anywhere.

## API Documentation

[pretty](index.html#) exposes a single function, the [pretty](index.html#) function itself. It's function
signature is `pretty(value, options)`. `value` can be any Lua value. `options`
must be a table.

[pretty](index.html#) is sure to complain if you give it an unknown option, or if you give an
option a bad value.

- `indent: string`: The string to indent with. Four spaces by default.

## TODO

Tasks to be done before [pretty](index.html#) can be called version 1.0.0, in order of
priority:

- [ ] Add dedicated unicode submodule, to handle some minor alignment and
    character escaping issues. [pretty](index.html#) should escape all malformed unicode
    sequences.
- [ ] Align numbers towards right for tabular views.
- [ ] Add support for [setmetatable](https://www.lua.org/manual/5.1/manual.html#pdf-setmetatable), and exploring values in metatables.
- [ ] Provide nice formatting for `cdata` datatype in LuaJIT.
- [ ] Find a better name than [pretty](index.html#).
- [ ] Enhance internal structure some amount. See `TODO` markers in files.

It would be nice to have the following, but these are secondary:

- [ ] Add option for colored output. Primarily syntax highlighting, but also
    [BlueJ-style](www.bluej.org/about.html) scope highlighting, with some faint
    background colors.
- [ ] Expand on the comment output in output, for `__tostring` methods, and
    global namespaces like [io](https://www.lua.org/manual/5.1/manual.html#5.7) or [math](https://www.lua.org/manual/5.1/manual.html#5.6).
- [ ] Fit output within a predefined width limit. Default to 80.
- [ ] Look into tool for understanding complex structures with recursive
    definitions. Whatever modes are thought up, they should be automatic modes, not
    an options. Should at least include modes for self-referential tables and
    Directed-Acyclic-Graphs.

## Alternative pretty printers

[pretty](index.html#) is large, slow, and requires the debug library to work. It's not
designed for serialization purposes, nor is it concerned with offering the same
level of customization as other libraries do.

If you want a sleek, fast, customizable or embeddable library, there are
thankfully other options.

- [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.

Even more are available at [the lua-users wiki](lua-users.org/wiki/TableSerialization).

## Thoughts on displaying tables in an intuitive way.

Lua's table data-structure is likely to be the most concise data structure ever
invented. (If not, please send me a link!) Lists, maps, objects, classes,
proxies, etc. This obviously brings about it some difficulty when attempting to
represent these tables. What do we want to highlight, and what do we choose to
avoid?

One notable issue is whether to show every key that a table answers (to lift
some Smalltalk terms) to, or to just display those it contains. That is, do we
think about `__index` in the table's metatable and what it returns, or do we
ignore `__index`? For cases where `__index` is a function, we cannot say
anything about the keys that the table answers to. If `__index` is a table, we
have a better idea, but it would be cluttered to display both types of keys side
by side.

1. Native representation: Lua's native representation includes the type and
    address of the table. It allows for distinguishing between unique tables,
    but won't tell us anything about the contents.
1. Omission: By representing tables as the pseudo-parsable `{...}`, it's
    clear we are talking about a table. We disregard the ability to
    distinguish between tables.
1. If the table is empty, we could represent it as `{}`. But what if the table
    has a metatable with `__index` defined? We could continue to represent it as
    `{}`, but `{...}` would be more "honest".
1. Single-line: TODO
1. Multi-line: TODO
1. Columns: For some highly-regular structures, like lists of short strings,
    giving each string it's own line would be too long, but formatting them as a
    single-line list would be too cluttered. Thus we can take inspiration from
    the classic `ls` unix tool, and place the output into columns, to help guide
    the eyes.
1. Tabular: Other structures are formatted like actual tables of data, e.g. a
    sequence of tuples, like one would see in an SQL database. For these
    structures it's an obvious choice to align them based on the keys.
1. Pseudo-Tabular: Some structures are almost tabular, e.g. they are sequences
    of tuples, but some of the tuples differ in their structure. For these
    structures it's still useful to tabulate the keys that all tuples share. To
    do this we should sort the key order descending by the number of tuples with
    the key.
    But what do we do about the the outlier keys? We can either justify the
    entire table, and give specific spots for the outlier keys, thereby
    significantly increasing the size of the table, or we can leave the table
    unjustified, abandoning it's eye-guiding attributes.
1. Special cases: (Array-tree, Table-Tree, Linked-List, Predictive Sequences) TODO

# License

```
"THE BEER-WARE LICENSE" (Revision 42):

<jonjmaa@gmail.com> wrote this program.  As long as you retain this notice you
can do whatever you want with this stuff. If we meet some day, and you think
this stuff is worth it, you can buy me a beer in return.

 Jon Michael Aanes
```