elan is a small tool for managing your installations of the Lean theorem prover. It places lean and lake binaries in your PATH that automatically select and, if necessary, download the Lean version described in your project's lean-toolchain file. You can also install, select, run, and uninstall Lean versions manually using the commands of the elan executable.

~/my/package $ cat lean-toolchain
nightly-2023-06-27

~/my/package $ lake --version
info: downloading component 'lean'
Total: 181.0 MiB Speed:  17.7 MiB/s
info: installing component 'lean'
Lake version 4.1.0-pre (Lean version 4.0.0-nightly-2023-06-27)

~/my/package $ elan show
installed toolchains
--------------------

nightly (default)
nightly-2022-06-27

active toolchain
----------------

nightly-2023-06-27 (overridden by '/home/me/my/package/lean-toolchain')
Lean (version 4.0.0-nightly-2023-06-27, commit bb8cc08de85f, Release)

Linux/macOS/Cygwin/MSYS2/git bash/...: run the following command in a terminal:

curl https://raw.githubusercontent.com/leanprover/elan/master/elan-init.sh -sSf | sh

Windows: run the following commands in a terminal (Command Prompt or PowerShell ≥ version 7.4.1):

curl -O --location https://raw.githubusercontent.com/leanprover/elan/master/elan-init.ps1
powershell -ExecutionPolicy Bypass -f elan-init.ps1
del elan-init.ps1

Alternatively, on any supported platform: Grab the latest release for your platform, unpack it, and run the contained installation program.

The installation will tell you where it will install elan to (~/.elan by default), and also ask you about editing your shell config to extend PATH. elan can be uninstalled via elan self uninstall, which should revert these changes.

The toolchains downloaded by elan require some patching on NixOS, which is done automatically by the version available in Nixpkgs.

$ nix-env -iA nixpkgs.elan

On some systems, lake will not work out of the box even if installed through elan:

• You'll need git to download dependencies through lake.

elan is basically a fork of rustup. Apart from new features and adaptions to the Lean infrastructure, these are the basic changes to the original code:

• Replaced every mention of rustup with elan, cargo with lake, and rust(c) with lean
• Merged CARGO_HOME and RUSTUP_HOME
• Removed options to configure host triple

If you want to build elan from source, you will need to install Rust and Cargo and run the following:

cargo build

The elan-init installer will show up in target/debug. This is also the main elan executable, so can test that it works by running the following:

ln -s ./target/debug/elan-init ./elan
./elan --help

The windows build requires a 64-bit developer command prompt and a Windows version of perl.exe which you can download from https://strawberryperl.com/. Make sure this downloaded perl.exe is the first thing in your PATH so that the build does not try and use C:\Program Files\Git\usr\bin\perl.exe. The git provided version of perl doesn't work for some reason.

Then you can run cargo build as shown above.