From the post: "I’m aware of typed languages that compile to Lua, but here’s a native approach."

Regarding teal specifically: It currently doesn't support union types as described in the post (see the 'Current limitations of union types' section of the tutorial: https://pdesaulniers.github.io/tl/tutorial.html

Lack of tooling/LSP support compared to Lua. A rather popular neovim plugin, gitsigns, recently switched from teal to regular lua because, at least in part, the type annotations available via lua-language-server.

https://github.com/lewis6991/gitsigns.nvim/commit/4d63d996b0...