Add support for Lean

[juanbelieni]

Is there an existing issue for this?

• [X] I have searched the existing issues

What is the missing lexer?

Lean is a functional programming language and a proof assistant.

According to the Lean Community Website, they are currently in the middle of switching from using Lean 3 to using Lean 4. Because of this, I propose to have the lean3 and lean4 lexers, and a lean lexer that will be a fallback to lean4.

In the Pygments languages page, it says that it has support for Lean, but I don't know yet how easy it is to port from Pygments to Chroma.

The reference manual for the language can be found here.

Links to existing syntax definitions

• Emacs plugin syntax
• neovim plugin syntax