mt_repl is a Minetest mod that provides a Lua read–eval–print loop (REPL). You can type Lua statements or expressions and see the results in your favorite terminal emulator while Minetest is running. mt_repl is intended as a tool for debugging other mods.

Features

• Automatic return (e.g., you can just type 2 + 2 instead of return 2 + 2 or =2 + 2)

• Pretty-printing:

  ~~> minetest.get_player_by_name('singleplayer'):getpos()
  {
    x = 133.19999694824,
    y = -2.5,
    z = -62.799999237061
  }

• GNU Readline support (including persistent history)
• Custom startup files
• A MoonScript input mode, with assignment to global variables by default (as in plain Lua)

Caveats

• I've only tested it on Linux, and it's implemented in a way that it probably won't work on non-Unix-likes (it uses named pipes and luaposix).
• I've only tested it in single-player mode. There is no sandboxing. Don't enable this mod on a multiplayer server if you don't trust the other players not to erase your home directory.
• Multi-line commands aren't allowed.
• print will use the Minetest server's standard output, which isn't the terminal you're looking at while you're using the REPL.
• In MoonScript, creating local variables is not possible. Even local declarations don't work.

Installation

Minetest versions 0.4.7 and later should be supported.

• Install the Lua modules luaposix and inspect.lua. (luaposix is also available as the Debian package lua-posix.) MoonScript is optional.
• Install the mod like an ordinary Minetest mod.

• Set the environment variables MT_REPL_FIFO_REPL_TO_MT and MT_REPL_FIFO_MT_TO_REPL to the paths of a pair of named pipes. I recommend doing this by putting

  export MT_REPL_FIFO_REPL_TO_MT="$HOME/.minetest/mods/mt_repl/fifo_repl_to_mt"
  export MT_REPL_FIFO_MT_TO_REPL="$HOME/.minetest/mods/mt_repl/fifo_mt_to_repl"

  in your .bashrc or whatever, then saying:

  $ mkfifo "$MT_REPL_FIFO_REPL_TO_MT"
  $ mkfifo "$MT_REPL_FIFO_MT_TO_REPL"

Usage

When the mod is enabled, use the chat command /repl in-game, then run the included Python script repl.py in another terminal window, which should display a prompt.

To quit from the Python script, hit Control-D to signal EOF or enter the special input quit. This will also terminate the REPL on the Minetest side, so you'll need to restart it (by saying /repl) if you want to use it again.

If you put a Lua script named .mt_replrc in your home directory, it will be run each time the REPL starts up. See rc-example.lua.

To use MoonScript instead of Lua, set mt_repl_use_moonscript = true in your .mt_replrc (.mt_replrc itself must still be in Lua). Here's a hint for writing MoonScript one-liners: you can squeeze multiple statements into a place where only one is allowed by abusing do like so:

if 1 + 1 == 2 then do a = 1, do b = 2 else c = 3

License

This program is copyright 2013 Kodi Arfer.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details.