Copilot: Stream DSL for hard real-time runtime verification

Copilot is a runtime verification framework written in Haskell. It allows the user to write programs in a simple but powerful way using a stream-based approach.

Programs can be interpreted for testing, or translated into C99 code to be incorporated in a project or as a standalone application. The C99 backend output is constant in memory and time, making it suitable for systems with hard realtime requirements.

Using Copilot

Assuming you have GHC and cabal already installed (see Haskell Platform or ghcup), there are several ways to use Copilot:

• Adding Copilot to your project

  Copilot is available from Hackage. Adding copilot to your project's cabal file should be enough to get going.

• Adding Copilot to the default GHC environment

  cabal v2-install --lib copilot
  

  After which Copilot will be available from ghci.

• Launching a repl with Copilot

  Another quick solution is to cabal to launch a repl with Copilot available.

  cabal v2-repl --build-depends copilot
  

  Cabal will download and build Copilot only to make it available in the launched repl. The global GHC environment will not be affected.

• Building from source (typically done for development):

  git clone https://github.com/Copilot-Language/copilot.git
  cd copilot
  git submodule update --init --remote
  

  Compiling can either be done in a Nix-style build, or a traditional one:

  Nix-Style build (Cabal >= 2.x)

  cabal build       # For Cabal 3.x
  cabal v2-build    # For Cabal 2.x
  

  Traditional build (Cabal 1.x)

  cabal install --dependencies-only
  cabal build
  

Note there is a TravisCI build (linked to at the top of this README) if you have trouble building/installing.

Example

Here follows a simple example of a heating system. Other examples can be found in the examples directory of the main repository.

-- This is a simple example with basic usage. It implements a simple home
-- heating system: It heats when temp gets too low, and stops when it is high
-- enough. It read temperature as a byte (range -50C to 100C) and translates
-- this to Celcius.

module Heater where

import Language.Copilot
import Copilot.Compile.C99

import Prelude hiding ((>), (<), div)

-- External temperature as a byte, range of -50C to 100C
temp :: Stream Word8
temp = extern "temperature" Nothing

-- Calculate temperature in Celcius.
-- We need to cast the Word8 to a Float. Note that it is an unsafeCast, as there
-- is no direct relation between Word8 and Float.
ctemp :: Stream Float
ctemp = (unsafeCast temp) * (150.0 / 255.0) - 50.0

spec = do
  -- Triggers that fire when the ctemp is too low or too high,
  -- pass the current ctemp as an argument.
  trigger "heaton"  (ctemp < 18.0) [arg ctemp]
  trigger "heatoff" (ctemp > 21.0) [arg ctemp]

-- Compile the spec
main = reify spec >>= compile "heater"

The examples located in the examples/ directory can be run from the root of the project. Each example has a name. As a rule of thumb, the examples are named after the filename (without extension) in lowercase letters, and directory seperators replaced with a '-'. For example:

cabal run addmult -f examples
cabal run counter -f examples
cabal run what4-arithmetic -f examples

Contributions

Feel free to open new issues and send pull requests.

In order to contribute to Copilot, please use the following steps which will make the process of evaluating and including your changes much easier:

• Create an issue for every individual change or problem with Copilot. Document the issue well.

• Always comment on the issues you are addressing in every commit. Be descriptive, and use the syntax #<issue_number> so that we can track changes and issues easily.

• Every commit should mention one issue and, ideally, only one.

• Do not send a PR or commit that addresses multiple problems, unless they are related and cannot be separated.

• Do not commit to master directly, except for branch merges. Make sure you always merge onto master using --no-ff so that we can tell that features were addressed separately, completed, tested, and then merged. If you are a Copilot developer, create a branch for every issue you are addressing, complete it, and then merge onto master. Document every commit in every branch, including the last merge commit, stating the issues it addresses or closes.

This process is similar to Git Flow. The equivalent of Git Flow's master branch is our latest tag, and the equivalent of Git Flow's develop branch is our master.

Further information

For further information, including documentation and a tutorial, please visit the Copilot website: https://copilot-language.github.io.

Acknowledgements

We are grateful for NASA Contract NNL08AD13T to Galois, Inc. and the National Institute of Aerospace, which partially supported this work.

Additionally NASA Langley contracts 80LARC17C0004 and NNL09AA00A supported further development of Copilot.

License

Copilot is distributed under the BSD-3-Clause license, which can be found here.

The Copilot Team

The development of Copilot spans across several years. During these years the following people have helped develop Copilot (in no particular order):

• Lee Pike
• Alwyn Goodloe (maintainer)
• Robin Morisset
• Sebastian Niller
• Nis Wegmann
• Chris Hathhorn
• Eli Mendelson
• Jonathan Laurent
• Laura Titolo
• Georges-Axel Jolayan
• Macallan Cruff
• Ryan Spring
• Lauren Pick
• Frank Dedden (maintainer: contact at [email protected])
• Ivan Perez (maintainer)