This crate requires a nightly (unstable, experimental) compiler version. To switch to it, you must have Rust installed via Rustup, and run:
rustup default nightly
Run rustup default stable to switch back.
Installing the command-line executable
Assuming you have Rust/Cargo installed, run this command in a terminal:
cargo install ley
It will make the ley command available in your PATH if you've allowed the PATH to be modified when installing Rust. cargo uninstall ley uninstalls.
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