luaprompt

Copyright (C) 2012-2023 Dimitris Papavasileiou <dpapavas@protonmail.ch>

luaprompt is both an interactive Lua prompt that can be used instead
of the official interpreter, as well as a module that provides a Lua
command prompt that can be embedded in a host application.  As a
standalone interpreter it provides many conveniences that are missing
from the official Lua interpreter.  As an embedded prompt, it's meant
for applications that use Lua as a configuration or interface language
and can therefore benefit from an interactive prompt for debugging or
regular use.

luaprompt features:

* Readline-based input with history and completion: In particular all
  keywords, global variables and table accesses (with string or
  integer keys) can be completed in addition to readline's standard
  file completion.  Module names are also completed, for modules
  installed in the standard directories, and completed modules can
  optionally be loaded.

* Persistent command history (retained across sessions), as well as
  recording of command results for future reference.

* Proper value pretty-printing for interactive use: When an expression
  is entered at the prompt, all returned values are printed
  (prepending with an equal sign is not required).  Values are printed
  in a descriptive way that tries to be as readable as possible.  The
  formatting tries to mimic Lua code (this is done to minimize
  ambiguities and no guarantees are made that it is valid code).

* Color highlighting of error messages and variable printouts.

Installation
============

luaprompt is available as a rock.  It can be installed via LuaRocks with:

    luarocks install luaprompt

Alternatively, you can customize the behavior as described in the
"Configuration" section.  Start by downloading and unpacking the
sources with:

    luarocks unpack luaprompt

Change to the directory it was downloaded to, edit the rockspec file
to add, remove or change the default configuration macros, and then
build and install with:

    luarocks make <rockspec-file>

Standalone usage
================

Besides the luaprompt module, the rock contains a standalone
interpreter based on luaprompt. It tries to mimic the standard Lua
interpreter as much as possible (currently only the -E flag is not
supported) while providing the extra set of features described above.
          
To invoke the interpreter, simply type "luap" instead of "lua" on the
command line.  A file with custom configuration, or startup actions
can be placed either at "~/.luaprc.lua", or, alternatively, at
"~/.config/luaprc.lua".  The first of these to be found is loaded and
executed at startup.

As an example, an rc file setting alternate prompts and history file
locations, would contain something like the following:

local prompt = require "prompt"
prompt.history = "/tmp/lua_history"
prompt.prompts = {"%  ", "%% "}

The prompt module
=================
     
Using the module is pretty straightforward, as it essentially wraps
the calls described in the section on embedding luaprompt below.  This
functionality is available, either in variables which can be set or
queried, or in Lua functions.  An example session, which covers
everything and should be self-explanatory, follows:

> prompt = require "prompt"
> prompt.colorize = true
> prompt.name = "myprompt"
> prompt.history = "/tmp/.myprompt_history"
> prompt.prompts = {
>>    function () return string.format("(%d)%% ", os.time()) end,
>>    "%% "
>> }
> prompt.enter()
%   _G[nil] = 
%% nil
myprompt:2: table index is nil

Stack trace:
	#0 [C]: in function '__newindex'
	#1 myprompt:2: in the main chunk
	#2 [C]: in function 'enter'
	#3 stdin:1: in the main chunk
	#4 [C]: in function ?

% ^D 
>

One can also use just the pretty-printer of luaprompt, by calling
prompt.describe, which returns a string with a pretty print-out of the
argument.  For example:

> =prompt.describe(coroutine)
{ 
  create = <function: 0x41a8b0>,
  yield = <function: 0x41a630>,
  wrap = <function: 0x41a910>,
  running = <function: 0x41a890>,
  resume = <function: 0x41a9e0>,
  status = <function: 0x41a770>,
}

Configuration
=============

You can customize luaprompts command line interface, as it is based on
GNU Readline.  This includes the ability to change behavior, such as
how completion is performed, define additional keybindings or redefine
existing ones, define custom macros and other possibilities.  It is
therefore highly recommended to consult the Readline's documentation
for more information.

Note that luaprompt sets its application name, so that you can have
custom Readline configuration, that will be effective for luaprompt
only (thus not affecting every other Readline-enabled application on
your system).  You can achieve that using $if ... $endif conditional
constructs within Readline's initialization file.  Again, see
Readline's documentation for more information.

At build time, you can use several macros in order to configure
luaprompt's functionality, by defining them in your Makefile.  For
instance, to pass the macro MACRO_NAME to the compiler, simply add
-DMACRO_NAME, or -DMACRO_WITH_VALUE=\"value\" to the compile flags.

The following macros control auto-completion:

COMPLETE_KEYWORDS:       Keywords such as for, while, etc
COMPLETE_MODULES:        Module names
COMPLETE_TABLE_KEYS:     Table keys, including global variables
COMPLETE_METATABLE_KEYS: Keys in the __index metafield, if it
                         exists and is a table
COMPLETE_FILE_NAMES:     File names

Define SAVE_RESULTS to enable tracking of results.  When enabled each
returned value, that is, each value the prompt prints out, is also
added to a table for future reference.

The name of the table holding the results can be configured by
defining RESULTS_TABLE_NAME to the desired table name (as a C string).

The table holding the results, can also be made to have weak values,
so as not to interfere with garbage collection.  To enable this,
define WEAK_RESULTS.

Uncomment the following line and customize the prefix as desired to

You can keep the auto-completer from considering certain table keys
(and hence global variables) for completion, based on their prefix.
To enable this behavior, define HIDDEN_KEY_PREFIX to the desired
prefix (as a C string).

When completing certain kinds of values, such as tables or
functions, the completer also appends certain useful suffixes such
as '.', '[' or '('. Normally these are appended only when the
value's name has already been fully entered, or previously fully
completed, so that one can still complete the name without the
suffix.  In order to append the suffix, one then only has to press
the completion key one more time.

Define ALWAYS_APPEND_SUFFIXES to make the completer always append
these suffixes.

The autocompleter can complete module names, as if they were already
require'd and available as a global variable.  Once the module name is
fully completed, a further tab press loads the module and exports it
as a global variable so that all further tab-completions now apply to
the module's table.

You can disable this functionality, by defining NO_MODULE_LOAD.
Module names will then only be completed inside strings (for use with
require).

To make the auto-completer ask for confirmation before loading or
globalizing a module, define CONFIRM_MODULE_LOAD.

Embedded Usage
==============

To embed luaprompt into a host application, simply compile and link
prompt.c with your sources.  A POSIX environment is assumed and GNU
Readline is required for proper command line editing.  If it is
provided, you should define the macros HAVE_LIBREADLINE and
HAVE_READLINE_HISTORY.  You should also define HAVE_IOCTL, unless your
environment doesn't support the TIOCGWINSZ ioctl call to get the
terminal width.

The API is very simple:

void luap_enter (lua_State *L)
Call this to begin an interactive session.  The session can be
terminated with Ctrl-D.

void luap_setname (lua_State *L, const char *name)
Set the name of the application.  This is basically the chunk name
displayed with error messages.  The default program name is "lua".

void luap_setprompts (lua_State *L, const char *single, char *multi)
Provide two prompts, one for single-line and one for multi-line
input. The defaults prompts are "> " and ">> ".

void luap_setpromptfuncs (lua_State *L)
Pops two values off the stack and, if they're functions, uses them as
prompt generators, for single and multi-line prompts respectively.  If
any of the supplied values are not functions, the prompts set via
luap_setprompts above, or the last generated prompts are used.  The
supplied functions should return a string (which will be used as a
prompt).

void luap_sethistory (lua_State *L, const char *file) Set the file to
be used to perist the command history across sessions.  If this
function isn't called the command history is lost on session exit.
Note that the provided name is used as-is, that is, it is not expanded
as if it was entered at the shell so you cannot use a string of the
form "~/.lua_history" for example.

void luap_setcolor (lua_State *L, int enable)
Setting enable to zero disables color output.  Color output is enabled
by default if the output has not been redirected to a file or pipe.

There are also matching luap_get* calls, which work much like you'd
expect them to:

void luap_getprompts(lua_State *L, const char **single, const char **multi)
void luap_getpromptfuncs(lua_State *L)
void luap_gethistory(lua_State *L, const char **file)
void luap_getcolor(lua_State *L, int *enabled)
void luap_getname(lua_State *L, const char **name)

In addition to the above the following calls, which are meant for
internal use can be used by the host application as well if required.

char *luap_describe (lua_State *L, int index)
Returns a string with a human-readable serialization of the value at
the specified index.

int luap_call (lua_State *L, int n)
Calls a function with n arguments and provides a stack trace on error.
This is equivalent to calling lua_pcall with LUA_MULTRET.

License
=======

luaprompt is released under the terms and conditions of the MIT/X11
license.  See the LICENSE file for details.