LuaML: An experimental markup language and 'browser' for it

Demo of a simple structured editor for formatted text atop an infinite 2D surface that can be panned and zoomed.

For ease of implementation, LuaML documents are always legal Lua objects rather than a first-class language like HTML. A simple example:

{ type='text', data={'hello, world!',} }

Text object data consists of an array of strings, one for each line. No newlines at the moment. (Everything is subject to change.)

You can draw various shapes on the surface:

{type='line', data={0,0, 0,600}},
{type='line', data={0,0, 800,0}},
{type='text', data={'0'}, x=-20,y=-20},
{type='rectangle', x=50,y=50, w=20,h=80, r=1,g=0,b=0},
{type='text', data={'abc', 'def'}, x=150, y=50, w=50,h=50, fg={r=0,g=0.4, b=0.9}},
{type='circle', x=300,y=200, radius=40, r=1,g=0,b=1},
{type='arc', x=0,y=0, radius=50, angle1=0, angle2=math.pi*2/3},
{type='ellipse', x=100,y=100, radiusx=10, radiusy=50},
{type='bezier', data={25,25, 25,125, 75,25, 125,25}},

But most of the design effort so far has focused on the 3 text types:

• text for runs of text to be line-wrapped over the given width.
• rows and cols, the only hierarchical types, ways to compose text nodes into various grid layouts.

Some more examples.

Adjust foreground/background color (akin to a div with inline style):

{ type='text', fg={r=1,g=0,b=0}, bg={r=1,g=1,b=0},
  data={'hello, world!'}
}

Two-column text:

{ type='cols', data={
  {type='text', data={'first column'}},
  {type='text', data={'second column'}},
}}

A table with two rows and two columns:

{ type='cols', data={
  { type='rows', data={
    {type='text', data={'abc'}},
    {type='text', data={'def'}},
  }},
  { type='rows', data={
    {type='text', data={'ghi'}},
    {type='text', data={'jkl'}},
  }},
}}

(With the current design, cols of rows seem strictly superior to rows of cols. Column boundaries line up consistently across rows.)

This is still quite incomplete. Come help figure out its future. Currently supported "attributes":

• fg, bg for color (no blink tag yet)
• margin (used as margin-left or margin-top depending on whether the parent node has cols or rows respectively)
• width in pixels (I'd like to add '%' units here.)

Since this is all Lua, unrecognized attributes are silently ignored. In the app itself you'll see attributes like name and doc. (This is a nightmare if you imagine this turning into some sort of long-lived standard with versions and compatibility guarantees. I don't. I just want an app-internal format for creating UIs with very little code.)

LuaML.love is a fork of lines.love, an editor for plain text where you can also seamlessly insert line drawings. Designed above all to be easy to modify and give you early warning if your modifications break something.

Getting started

Install LÖVE. It's just a 5MB download, open-source and extremely well-behaved. I'll assume below that you can invoke it using the love command, but that might vary depending on your OS.

Run this app from the terminal, passing its directory to LÖVE

You'll see a page that's currently hard-coded in the app.

All text is currently editable. There's a table on the right that will grow and shrink as you add and delete text.

Changes you make are currently not saved. This is just a demo.

To pan, drag the surface around. To increase/decrease zoom, press ctrl+=, ctrl+- respectively. To reset zoom press ctrl+0.

To edit formatting you'll need to modify the code for the app. To do this live without restarting the app each time, download the driver app. Here's an example session using a fork of this repo:

More information about the on-disk representation of freewheeling apps.

Keyboard shortcuts

While editing text:

• ctrl+f to find patterns within a file
• ctrl+c to copy, ctrl+x to cut, ctrl+v to paste
• ctrl+z to undo, ctrl+y to redo
• ctrl+= to zoom in, ctrl+- to zoom out, ctrl+0 to reset zoom
• alt+right/alt+left to jump to the next/previous word, respectively
• mouse drag or shift + movement to select text, ctrl+a to select all

Exclusively tested so far with a US keyboard layout. If you use a different layout, please let me know if things worked, or if you found anything amiss: http://akkartik.name/contact

When cursor is not in an editor:

• arrow keys pan the surface
• shift+arrow keys pan faster
  • pagedown and pageup are aliases for shift+down and shift+up respectively

Known issues

• Both freewheeling apps and the driver for them currently benefit from being launched in terminal windows rather than by being clicked on in a desktop OS. See the driver app for details.

• No support yet for Unicode graphemes spanning multiple codepoints.

• No support yet for right-to-left languages.

• Undo/redo may be sluggish in large files. Large files may grow sluggish in other ways. Works well in all circumstances with files under 50KB.

• If you kill the process, say by force-quitting because things things get sluggish, you can lose data.

• Long wrapping lines can't yet distinguish between the cursor at end of one screen line and start of the next, so clicking the mouse to position the cursor can very occasionally do the wrong thing.

• Can't scroll while selecting text with mouse.

• No scrollbars yet. That stuff is hard.

Mirrors and Forks

This repo is a fork of lines.love, an editor for plain text where you can also seamlessly insert line drawings. Its immediate upstream is the template repo for freewheeling apps. Updates to it can be downloaded from the following mirrors:

• https://git.sr.ht/~akkartik/luaML.love
• https://codeberg.org/akkartik/luaML.love

Further forks are encouraged. If you show me your fork, I'll link to it here.

• https://git.sr.ht/~akkartik/driver.love - the driver app for modifying freewheeling apps without restarting them.

Feedback

Most appreciated.