Quickstart

These instructions will walk you through setting up Lean using the "basic" setup and VS Code as the editor. See Setup for other ways, supported platforms, and more details on setting up Lean.

  1. Install VS Code.

  2. Launch VS Code and install the lean4 extension.

    installing the vscode-lean4 extension

  3. Create a new file using "File > New Text File" (Ctrl+N). Click the Select a language prompt, type in lean4, and hit ENTER. You should see the following popup: elan

    Click the "Install Lean using Elan" button. You should see some progress output like this:

    info: syncing channel updates for 'nightly'
    info: latest update on nightly, lean version nightly-2021-12-05
    info: downloading component 'lean'
    
  4. While it is installing, you can paste the following Lean program into the new file:

    #eval Lean.versionString
    

    When the installation has finished, the Lean Language Server should start automatically and you should get syntax-highlighting and a "Lean Infoview" popping up on the right. You will see the output of the #eval statement when you place your cursor at the end of the statement.

    successful setup

You are set up!

Create a Lean Project

You can now create a Lean project in a new folder. Run lake init foo from "View > Terminal" to create a package, followed by lake build to get an executable version of your Lean program. On Linux/macOS, you first have to follow the instructions printed by the Lean installation or log out and in again for the Lean executables to be available in you terminal.

Note: Packages have to be opened using "File > Open Folder..." for imports to work. Saved changes are visible in other files after running "Lean 4: Refresh File Dependencies" (Ctrl+Shift+X).

Troubleshooting

The InfoView says "Waiting for Lean server to start..." forever.

Check that the VS Code Terminal is not showing some installation errors from elan. If that doesn't work, try also running the VS Code command Developer: Reload Window.