In the context of Elixir/Erlang, NIF stands for Native Implemented Function. NIFs are a way to implement Erlang/Elixir functions in native code (typically C or Rust) for performance-critical operations or to interface with system libraries.

Rustler is a tool for safely writing NIFs in Rust. The structure of this repo is due to the way the Rustler library works.

risc0/
├── lib/
│   ├── risc0.ex
│   └── risc0/
│       └── risc0.ex
└── native/
    └── risc0_prover/
        ├── Cargo.toml
        └── src/
            ├── Cargo.toml
            └── src/
                └── lib.rs

NIF for Elixir.Risc0

To build the NIF module:

• Your NIF will now build along with your project.

To load the NIF:

defmodule Risc0.Risc0Prover do
  use Rustler, otp_app: :risc0, crate: :risc0_prover

  # When your NIF is loaded, it will override this function.
  def prove(_arg1, _arg2), do: :erlang.nif_error(:nif_not_loaded)
  def verify(_arg1, _arg2), do: :erlang.nif_error(:nif_not_loaded)
end

To test the NIF:

• You must have the risc0-zkvm toolchain installed.
• Compile the compliance circuit with cargo build in the compliance_circuit directory. This is necessary to generate the guest ELF and ID files.
• If you are on macOS, you must have XCode installed. To build with the prove flag on macOS, you'll need to have the full version of XCode installed, which includes the 'metal' compiler. We need the prove feature flag to have the proving happen in the same process. Otherwise, with default feature flags, the prover will try to launch a r0vm server process to perform the actual proving. If you're calling this from some other environment, it will throw a "No child processses" error. If you encounter the compilation error "xcrun: error: unable to find utility "metal", not a developer tool or in PATH" and xcode-select --print-path prints /Library/Developer/CommandLineTools, running sudo xcode-select --switch /Applications/Xcode.app/Contents/Developer can fix it.
• You can run the tests with mix test.