warning Experimental
This is a highly experimental feature still under active development. It is documented here primarily for the real early adopters as this feature develops.
If you want to experiment, be sure to use the edge builds.
Space Lua is a custom implementation of the Lua programming language, embedded in SilverBullet. It aims to be a largely complete Lua implementation, and adds a few non-standard features while remaining syntactically compatible with “real” Lua.
url: https://youtu.be/t1oy_41bDAY
Goals
The introduction of Lua aims to unify and simplify a few SilverBullet features, specifically:- Scripting: replace Space Script (JavaScript) with a more controlled, simple and extensible language.
- Replace Expression Language, Template Language and Query Language with Lua-based equivalents.
- (Potentially) provide an alternative way to specify Space Config
Strategy
This is a big effort. During its development, Space Lua will be offered as a kind of “alternative universe” to the things mentioned above. Existing Live Templates, Live Queries and Space Script will continue to work as before, unaltered.Once these features stabilize and best practices are ironed out, old mechanisms will likely be deprecated and possibly removed at some point.
We’re not there yet, though.
Basics
In its essence, Space Lua adds two features to its Markdown language:- Definitions: Code written in space-lua code blocks are enabled across your entire space.
- Expressions: The ${expression} syntax will Live Preview to its evaluated value.
Definitions
Space Lua definitions are defined in fenced code blocks, in this case with the space-lua language. As follows:-- adds two numbers
function adder(a, b)
return a + b
end
Each space-lua block has its own local scope. However, following Lua semantics, when functions and variables are not explicitly defined as local they will be available globally across your space. This means that the adder function above can be used in any other page.
Since there is a single global namespace, it is good practice to manually namespace things using the following pattern:
-- This initializes the stuff variable with an empty table if it's not already defined
stuff = stuff or {}
function stuff.adder(a, b)
return a + b
end
note Tip
All your space-lua scripts are loaded on boot, to reload them without reloading the page, simply run the command.
Expressions
A new syntax introduced with Space Lua is the ${lua expression} syntax that you can use in your pages. This syntax will Live Preview to the evaluation of that expression.For example: 10 + 2 = ${adder(10, 2)} (Alt-click, or select to see the expression) is using the just defined adder function to this rather impressive calculation. Yes, this may as well be written as ${10 + 2} (${10 + 2}), but... you know.
Queries
Space Lua has a feature called Lua Integrated Query, which integrate SQL-like queries into Lua. By using this feature, you can easily replicate Live Queries. More detail in Lua Integrated Query, but here’s a small example querying the last 3 modifies pages:${query[[
from index.tag "page"
order by lastModified desc
select name
limit 3
]]}
Widgets
The ${lua expression} syntax can be used to implement simple widgets. If the Lua expression evaluates to a simple string, it will live preview as that string rendered as markdown. However, if the expression returns a Lua table with specific keys, you can do some cooler stuff.The following keys are supported:
- markdown: Renders the value as markdown
- html: Renders the value as HTML
- cssClasses: Attach the specified CSS classes to this element (e.g. using CSS classes defined using Space Style).
- display: Render the value either inline or as a block (defaults to inline)
An example combining a few of these features:
function marquee(text)
return {
html= "<marquee>" .. text .. "</marquee>";
display="block";
cssClasses={"my-marquee"}
}
end
And some Space Style to style it:
.my-marquee {
color: purple;
}Now, let’s use it:
${marquee "Finally, marqeeeeeeee!"}
Oh boy, the times we live in!
Commands
Custom commands can be defined using command#command.define(commandDef):command.define {
name = "Hello World",
run = function()
editor.flashNotification "Hello world!"
event.dispatch("my-custom-event", {name="Pete"})
end
}Try it:
Event listeners
You can listen to events using event#event.listen(listenerDef):event.listen {
name = "my-custom-event";
run = function(e)
editor.flashNotification("Custom triggered: "
.. e.data.name)
end
}Space Lua Extensions
Space Lua currently introduces a few new features on top core Lua:- Lua Integrated Query, embedding a Query Language-like language into Lua itself
- Thread locals
Thread locals
There's a magic _CTX global variable available from which you can access useful context-specific values. Currently the following keys are available:- _CTX.currentPage providing access (in the client only) to the currently open page (PageMeta object)
- _CTX._GLOBAL providing access to the global scope
API
While in Space Script all syscalls are asynchronous and need to be called with await, this is happens transparently in Space Lua leading to cleaner code:
local function callSomeThings()
local text = space.readPage(editor.getCurrentPage())
print("Current page text", text)
end
Lua implementation notes
Space Lua is intended to be a more or less complete implementation of Lua 5.4. However, a few features are (still) missing:- goto and labels (not planned, goto considered harmful)
- coroutines (not planned, not useful in the SilverBullet context)
- _ENV (planned)
- Full metatable support (only partial now, planned)