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# 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](https://en.wikipedia.org/wiki/Brutalist_architecture)
attempt at packaging up simple [Lua](http://www.lua.org) apps with almost all
the stuff needed to edit and build them. You will need some Unix-like
platform[1] with a C compiler and the ncurses and openssl libraries.
Here's how you run one of the example apps (the [Tower of Hanoi](https://en.wikipedia.org/wiki/Tower_of_Hanoi)):
```
git clone https://github.com/akkartik/teliva
cd teliva
make linux
src/teliva hanoi.tlv
```
<img alt='screenshot of Teliva running the Towers of Hanoi' src='doc/hanoi.png'>
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. ([video](https://archive.org/details/akkartik-2021-11-14))
[1] Tested so far on Linux and Mac OSX; should also work on BSD, WSL on
Windows, etc.
## 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.
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. My priority is providing a good experience for newcomers to
comprehend and modify the programs they use. If it's not clear how to provide
that experience for some kinds of Lua programs, I'd rather disable support for
them in Teliva and let people use regular Lua. Or other platforms!
- This approach doesn't make sense for batch programs, I think. I also don't
yet have a good story for building server programs in this way.
- 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 (color, UTF-8) text-mode window for printing text to,
and a keyboard for reading unbuffered keystrokes from.
- Teliva doesn't use files, so the `require` keyword no longer makes sense.
You get some libraries preloaded (see below). Beyond those, apps should
include all Lua code they want to use. There's no affordance for adding
native (non-Lua) libraries.
- 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.
- To create a well-behaved sandbox, Teliva includes a small set of native
libraries and doesn't support adding more native libraries.
Teliva is not tested much at all yet. This is my first time programming either
in Lua or within Lua. So bug reports are most appreciated if Lua programs
behave unexpectedly under Teliva.
## What's included?
* [Lua 5.1](https://www.lua.org/manual/5.1)
* The [ncurses](https://tldp.org/HOWTO/NCURSES-Programming-HOWTO) library for
building text-mode user interfaces. ([Alternative documentation](https://tldp.org/LDP/lpg-0.4.pdf))
* The [Kilo](https://github.com/antirez/kilo) text editor, modified to use
ncurses. (Read more about it in this [fantastic walk-through](https://viewsourcecode.org/snaptoken/kilo).)
* The [lcurses](https://github.com/lcurses/lcurses) binding for ncurses (as
module `curses`).
* The [luasocket](https://w3.impa.br/~diego/software/luasocket) library of
networking primitives (modules `socket`, `http`, `url`, `headers`, `mime`,
`ltn12`).
* The [luasec](https://github.com/brunoos/luasec) library for HTTPS support
(modules `https` and `ssl`).
* The [json.lua](https://github.com/rxi/json.lua) library for
serializing/deserializing to JSON (module `json`).
The modules mentioned above are always available, just like standard Lua 5.1
libraries. They're available in their entirety with one exception:
* Some functions in lcurses have [additional smarts](https://github.com/lcurses/lcurses/blob/master/lib/curses.lua).
Teliva is [consistent with the underlying ncurses](https://github.com/akkartik/teliva/blob/main/src/lcurses/curses.lua).
While most things in these modules are currently available, I expect to delete
capabilities throughout this stack as I discover features that don't fit well
with the Teliva experience. If you find Teliva of use, please [introduce yourself](http://akkartik.name/contact)
to me so that I am aware of your use cases. Anybody who is interested can gain
a say in its future direction.
## What's with the name?
Teliva is the Tamil root for ‘clear’. Very much aspirational.
## Other apps to try out
* Conway's Game of Life, as an example of an animated local app.
```
src/teliva life.tlv
```
[video](https://merveilles.town/@akkartik/107277755421024772)
* A viewer for [LiChess TV](https://lichess.org/tv), as an example of
animation and accessing a remote API over a network.
```
src/teliva chesstv.tlv
```
[video](https://merveilles.town/@akkartik/107319684018301051)
## Feedback
[Most appreciated.](http://akkartik.name/contact)
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