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Creating a Lean project

Lean files are organized in projects called packages. The tool leanpkg manages project creation and dependencies. We will now create a new project depending on mathlib. The following commands should be typed in a terminal.

  • If you have not logged in since you installed Lean and mathlib, then you need to first type source ~/.profile.

  • Then go to a folder where you want to create a project in a subfolder my_project, and type:

     leanpkg new my_project
 cd my_project
 leanpkg add leanprover-community/mathlib
 update-mathlib

  • launch VScode, either through your application menu or by typing code

  • On the main screen, or in the File menu, click "Open folder" (on a Mac, just "Open"), and choose the folder my_project (not one of its subfolders).

  • Your Lean code should now be put inside files with extension .lean living in my_project/src/ or a subfolder thereof. In the file explorer on the left-hand side of VScode, you can right-click on src, choose New file, and type a filename to create a file there.

If you want to make sure everything is working, you can start by creating, say my_project/src/test.lean containing:

import topology.basic

#check topological_space

When the cursor is on the last line, the right hand part of VScode should display a "Lean messages" area saying: topological_space : Type u_1 → Type u_1

If, for some reason, you happen to loose the "Lean messages" area, you can get it back with "Ctrl-Shift-Enter". Also, you can get the Lean documentation inside VScode using "Ctrl-Shift-p" and then, inside the text field that appeared, type "lean doc" and hit Enter. Then click "Theorem proving in Lean" and enjoy.

Working on an existing package

Suppose you want to work on an existing project. As example, we will take the tutorial project. Open a terminal.

  • If you have not logged in since you installed Lean and mathlib, then you need to first type source ~/.profile.

  • Go the the directory where you would like this package to live.

  • Run git clone https://github.com/leanprover-community/tutorials.git.

  • This creates a directory named tutorials. Enter it with cd tutorials.

  • Type leanpkg configure to get leanpkg ready for use in this project.

  • Type update-mathlib to get mathlib ready for use in this project.

  • Type leanpkg build to compile everything, this should only take a few seconds.

  • launch VScode, either through your application menu or by typing code

  • On the main screen, or in the File menu, click "Open folder" (just "Open" on a Mac), and choose the folder tutorials (not one of its subfolders).

  • Using the file explorer on the left-hand side, explore everthing you want in tutorials/src