The Teal Programming Language

Your first Teal program

Let's start with a simple example, which declares a type-safe function. Let's call this example add.tl:

local function add(a: number, b: number): number
   return a + b
end

local s = add(1,2)
print(s)

You can type-check it with

tl check add.tl

You can convert it to Lua with

tl gen add.tl

This will produce add.lua. But you can also run it directly with

tl run add.tl

We can also write modules in Teal which we can load from Lua. Let's create our first module:

local addsub = {}

function addsub.add(a: number, b: number): number
   return a + b
end

function addsub.sub(a: number, b: number): number
   return a - b
end

return addsub

We can generate addsub.lua with

tl gen addsub.tl

and then require the addsub module from Lua normally. Or we can load the Teal package loader, which will allow require to load .tl files directly, without having to run tl gen first:

$ rm addsub.lua
$ lua
> tl = require("tl")
> tl.loader()
> addsub = require("addsub")
> print (addsub.add(10, 20))

When loading and running the Teal module from Lua, there is no type checking! Type checking will only happen when you run tl check or load a program with tl run.