Teliva - an environment for end-user programming

“Enable all people to modify the software they use in the course of using it.” — https://futureofcoding.org/episodes/033.html

“What if we, and all computer users, could reach in and modify our favorite apps?” — https://www.inkandswitch.com/end-user-programming

“Software must be as easy to change as it is to use.” — https://malleable.systems

What's this, then?

An extremely naïve, brutalist attempt at packaging up simple Lua (5.1) apps with all the stuff needed to edit and build them.

git clone https://github.com/akkartik/teliva
cd teliva
make linux
src/teliva hanoi.teliva

Here's an example app (the Tower of Hanoi):

No matter what app you run, you are always guaranteed access to a single obvious, consistent way (currently the hotkey ctrl-e) to edit its sources. And to run the updates after editing.

Toggle the same hotkey to restart the app with the new sources.

Over time I hope to improve the experience for error messages, failing tests, undoing changes and so on. The emphasis will be on maximizing hackability rather than functionality. I plan to be extremely parsimonious in taking on further dependencies. It should need just a Linux (or maybe some other Unix?) kernel, a C compiler, 12kLoC of Lua in this repo, ncurses.

Isn't this just an IDE?

There's one big difference: these apps are not intended to be runnable outside of the Teliva environment. Editing the sources will always be a core feature that's front and center in the UI.

At the moment this isn't much of a restriction given how trivial the differences with Lua are. You also don't get much benefit in exchange for taking on this restriction. Let's see if that changes.

A second, more subtle difference: it's primarily an environment for running apps, and only secondarily for editing them. Starting up the environment puts you in a running app by default. Creating an app from a clean slate is a low-priority use case, as is lots of specialized support for developing complex apps. The sweet spot for Teliva is simple apps that people will want to edit after using for a while.

Why Lua?

It's reputedly the fastest interpreted language per line of implementation code.

Will it run any Lua program?

Not quite.

This approach doesn't make sense for batch programs, I think.

I don't know how to obtain a simple, shallow graphics stack, so there's no support for graphics at the moment.

Teliva initializes the ncurses library by default, so apps should assume they have access to a text-mode window for printing text to, and a keyboard for reading unbuffered keystrokes from. Compare hanoi.teliva with hanoi.lua to get a sense for what changes are needed.

My plan is to disable support for certain Lua libraries as I gain experience programming in this way.

I want to provide sandboxed access to system resources (file system, network, etc.) which will likely create incompatibilities with the standard library. I'm disinclined to try to ‘improve’ on Lua syntax, however. It's not my favorite, but it's good enough.

Teliva is not tested much at all yet. This is my first time programming either in Lua or within Lua. Bug reports most appreciated.

Will it run any Ncurses program?

Probably not. Ncurses is extremely portable. I don't test on all the configurations Ncurses supports. For example, I assume terminals with UTF-8 support.

Will it run any Lua lcurses program?

There are some exceptions. For example, lcurses has some strange “smarts” that result in wgetch() not behaving like getch(). Teliva doesn't reproduce such bugs.

What's with the name?

Teliva is the Tamil root for ‘clear’. Very much aspirational.

Credits

This repository is an unholy union of:

• The Lua 5.1 programming language. (Documentation)
• The Ncurses library for building text-mode user interfaces. (Alternative documentation)
• The Lcurses library providing Lua bindings for Ncurses. (Documentation)
• The Kilo text editor. (With a fantastic walk-through.)

Send all praise to them, brickbats to me.

README for Lua 5.1

• What is Lua?

  Lua is a powerful, light-weight programming language designed for extending applications. Lua is also frequently used as a general-purpose, stand-alone language. Lua is free software.

  For complete information, visit Lua's web site at http://www.lua.org/ . For an executive summary, see http://www.lua.org/about.html .

  Lua has been used in many different projects around the world. For a short list, see http://www.lua.org/uses.html .

• Availability

  Lua is freely available for both academic and commercial purposes. See COPYRIGHT and http://www.lua.org/license.html for details. Lua can be downloaded at http://www.lua.org/download.html .

• Installation

  Lua is implemented in pure ANSI C, and compiles unmodified in all known platforms that have an ANSI C compiler. In most Unix-like platforms, simply do "make" with a suitable target. See INSTALL for detailed instructions.

• Origin

  Lua is developed at Lua.org, a laboratory of the Department of Computer Science of PUC-Rio (the Pontifical Catholic University of Rio de Janeiro in Brazil). For more information about the authors, see http://www.lua.org/authors.html .

README for Kilo

Kilo is a small text editor in less than 1K lines of code (counted with cloc).

A screencast is available here: https://asciinema.org/a/90r2i9bq8po03nazhqtsifksb

Usage: kilo

Keys:

CTRL-S: Save
CTRL-Q: Quit
CTRL-F: Find string in file (ESC to exit search, arrows to navigate)

Kilo does not depend on any library (not even curses). It uses fairly standard VT100 (and similar terminals) escape sequences. The project is in alpha stage and was written in just a few hours taking code from my other two projects, load81 and linenoise.

People are encouraged to use it as a starting point to write other editors or command line interfaces that are more advanced than the usual REPL style CLI.

Kilo was written by Salvatore Sanfilippo aka antirez and is released under the BSD 2 clause license.