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README.md
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README.md
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<!--- THIS IS AN AUTO-GENERATED FILE --->
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<!--- MANUAL CHANGES CAN AND WILL BE OVERWRITTEN --->
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# pretty is an advanced pretty printer for Lua.
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#
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It's primarily a
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[pretty](index.html#) is an advanced pretty printer for [Lua](https://lua.org).
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It's primarily a
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debugging tool, aiming for human readability, by detecting pattern in the input
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data, and creating an output string utilizing and highlighting those patterns.
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## Code Example
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Setup is simple, use pretty = require 'pretty', and you're good to go.
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Setup is simple, use `pretty = require 'pretty'`, and you're good to go.
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```
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$ print(pretty( { 1, 2, 3 } ))
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{ 1, 2, 3 }
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@ -35,67 +63,272 @@ builtin function (x)
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...
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end
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```
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## Motivation
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This project is the outcome of my frustration with existing pretty printers, and
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a desire to expand upon the pretty printer I developed for
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Xenoterm. The original Xenoterm pretty
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printer was much simpler than pretty - and the current is even simpler - but
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[Xenoterm](https://gitfub.space/takunomi/Xenoterm). The original Xenoterm pretty
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printer was much simpler than [pretty](index.html#) - and the current is even simpler - but
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the enhancements I make, when compared to other pretty printers, inspired me to
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create pretty.
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create [pretty](index.html#).
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[pretty](index.html#) sorts it's priorities like so:
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1. Human readability.
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1. Lua-compatible output.
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1. Customization.
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pretty sorts it's priorities like so:
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Human readability.
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Lua-compatible output.
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Customization.
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I'd rather have good defaults than provide a ton of customization options. If an
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structure avoids easy representation in Lua, I'd rather extend the syntax, than
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lose the info.
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Another aspect where pretty shines is in exploratory programming, when
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Another aspect where [pretty](index.html#) shines is in exploratory programming, when
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attempting to avoid reliance on outside documentation. The amount of information
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pretty exposes varies by the data you are inspecting. If you're inspecting
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[pretty](index.html#) exposes varies by the data you are inspecting. If you're inspecting
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a list of functions, their function signatures are visible, but if you're
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inspecting a single function, documentation and source location may appear if
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available.
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## Features
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Written in good-old pure-blood Lua, with support for PUC Lua 5.0+ and LuaJIT 2.0+.
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Redefining what it means to be "human readable":
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Is multi-line centric, to aid readability.
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Indention and alignment of keys-value pairs.
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Keys-value pairs are
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- Written in good-old pure-blood Lua, with support for PUC Lua 5.0+ and LuaJIT 2.0+.
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- Redefining what it means to be "human readable":
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- Is multi-line centric, to aid readability.
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- Indention and alignment of keys-value pairs.
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- Keys-value pairs are
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alpha-numerically sorted by key
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type and thereafter alphabetically.
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The format and structure of output changes depending upon the input. Maps
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- The format and structure of output changes depending upon the input. Maps
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appear differently to deeply nested tables to long sequences with short
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strings to short lists.
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Uses the standard debug library to gain information about functions and
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- Uses the standard debug library to gain information about functions and
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other advanced structures.
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## Installation
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pretty is loadable directly with require. Either clone or download this
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[pretty](index.html#) is loadable directly with [require](https://www.lua.org/manual/5.1/manual.html#pdf-require). Either clone or download this
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repository. Where you place it, depends upon what you want to do:
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**You want pretty in a specific project**: Place the pretty folder
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1. **You want pretty in a specific project**: Place the pretty folder
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somewhere in your project, and require it from one of your project files.
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**You want pretty on your system**: Place the pretty folder such that
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1. **You want pretty on your system**: Place the pretty folder such that
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it's visible from your Lua-path. On my system this might be
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/usr/local/share/lua/5.1/. Now you can require it from anywhere.
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## API Documentation
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pretty exposes a single function, the pretty function itself. It's function
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signature is pretty(value, options). value can be any Lua value. options
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[pretty](index.html#) exposes a single function, the [pretty](index.html#) function itself. It's function
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signature is `pretty(value, options)`. `value` can be any Lua value. `options`
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must be a table.
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[pretty](index.html#) is sure to complain if you give it an unknown option, or if you give an
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option a bad value.
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- indent: string: The string to indent with. Four spaces by default.
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## TODO
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Tasks to be done before [pretty](index.html#) can be called version 1.0.0, in order of
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priority:
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- [ ] Add dedicated unicode submodule, to handle some minor alignment and
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character escaping issues. pretty should escape all malformed unicode
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sequences.
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- [ ] Align numbers towards right for tabular views.
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- [ ] Add support for setmetatable, and exploring values in metatables.
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- [ ] Provide nice formatting for cdata datatype in LuaJIT.
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- [ ] Find a better name than pretty.
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- [ ] Enhance internal structure some amount. See TODO markers in files.
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It would be nice to have the following, but these are secondary:
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- [ ] Add option for colored output. Primarily syntax highlighting, but also
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BlueJ-style scope highlighting, with some faint
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background colors.
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- [ ] Expand on the comment output in output, for __tostring methods, and
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global namespaces like io or math.
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- [ ] Fit output within a predefined width limit. Default to 80.
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- [ ] Look into tool for understanding complex structures with recursive
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definitions. Whatever modes are thought up, they should be automatic modes, not
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an options. Should at least include modes for self-referential tables and
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Directed-Acyclic-Graphs.
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## Alternative pretty printers
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[pretty](index.html#) is large, slow, and requires the debug library to work. It's not
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designed for serialization purposes, nor is it concerned with offering the same
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level of customization as other libraries do.
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If you want a sleek, fast, customizable or embeddable library, there are
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thankfully other options.
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- inspect.lua: One of the classic debugging pretty printers.
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- pprint.lua: Reimplementation of inspect.lua
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- serpent: Advanced and fast pretty printer.
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- pluto: Can serialize arbitrary parts of
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Lua, including functions, upvalues, and proper lexical scoping. Not written in
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native Lua.
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- binser: Library for special purpose serialization.
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Even more are available at [the lua-users wiki](lua-users.org/wiki/TableSerialization).
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## Thoughts on displaying tables in an intuitive way.
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Lua's table data-structure is likely to be the most concise data structure ever
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invented. (If not, please send me a link!) Lists, maps, objects, classes,
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proxies, etc. This obviously brings about it some difficulty when attempting to
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represent these tables. What do we want to highlight, and what do we choose to
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avoid?
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One notable issue is whether to show every key that a table answers (to lift
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some Smalltalk terms) to, or to just display those it contains. That is, do we
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think about `__index` in the table's metatable and what it returns, or do we
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ignore `__index`? For cases where `__index` is a function, we cannot say
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anything about the keys that the table answers to. If `__index` is a table, we
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have a better idea, but it would be cluttered to display both types of keys side
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by side.
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1. Native representation: Lua's native representation includes the type and
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address of the table. It allows for distinguishing between unique tables,
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but won't tell us anything about the contents.
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1. Omission: By representing tables as the pseudo-parsable {...}, it's
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clear we are talking about a table. We disregard the ability to
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distinguish between tables.
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1. If the table is empty, we could represent it as {}. But what if the table
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has a metatable with __index defined? We could continue to represent it as
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{}, but {...} would be more "honest".
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1. Single-line: TODO
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1. Multi-line: TODO
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1. Columns: For some highly-regular structures, like lists of short strings,
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giving each string it's own line would be too long, but formatting them as a
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single-line list would be too cluttered. Thus we can take inspiration from
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the classic ls unix tool, and place the output into columns, to help guide
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the eyes.
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1. Tabular: Other structures are formatted like actual tables of data, e.g. a
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sequence of tuples, like one would see in an SQL database. For these
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structures it's an obvious choice to align them based on the keys.
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1. Pseudo-Tabular: Some structures are almost tabular, e.g. they are sequences
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of tuples, but some of the tuples differ in their structure. For these
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structures it's still useful to tabulate the keys that all tuples share. To
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do this we should sort the key order descending by the number of tuples with
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the key.
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But what do we do about the the outlier keys? We can either justify the
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entire table, and give specific spots for the outlier keys, thereby
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significantly increasing the size of the table, or we can leave the table
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unjustified, abandoning it's eye-guiding attributes.
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1. Special cases: (Array-tree, Table-Tree, Linked-List, Predictive Sequences) TODO
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# License
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```
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