A library for writing Plutus contracts and transforming them into executables that run on the app platform. The high-level workflow is this:

• Write a contract using the Plutus.Contract module. The type of contracts is ContractActions r => Contract r (), where PlutusContract r describes the actions it can perform. ContractActions is a list of common contract actions that includes waiting for blockchain events, exposing endpoints, and waiting for user actions. See the definition of Examples.Crowdfunding.crowdfunding for an example.
• (optional) Write traces for the contract using the Plutus.Contract.Emulator module. Traces are sequences of actions by simulated wallets that use the contract. Their signature is (MonadEmulator m) => ContractTrace m a (). See Examples.Game.lockTrace for an example.
• (optional) Write unit tests for the contract, using the Spec.HUnit module to make make assertions about traces.
• Turn the contract into an executable using the Plutus.Contract.App module. run :: Contract (ContractEffects '[]) () -> IO () takes a contract and turns it into an HTTP server with two routes, initialise and run. initialise responds to GET requests with the initial state of the contract. run expects POST requests of the old state together with an input event, and produces the new state. Plutus.Contract.App.runWithTraces takes a list of named traces whose intermediate states can be printed by calling the program with the trace argument and the name of a trace. The intermediate states so printed are JSON values that can be used as arguments for the run endpoint.

The /examples folder contains some hand-written examples for the use cases we currently have.

Contracts are represented by the Resumable f a type from Plutus.Contract.Resumable. f describes the effects that the contract can have. From the user's point of view, f is a list of effects (from extensible-effects) defined in Plutus.Contract.Effects and sub-modules. Internally, before running the contract, the entire list of effects is converted to a single Maybe i -> Either o a function, where i is a union of all possible inputs to the contract, and o is an output describing what inputs are currently expected. For example, o could say "I am currently waiting to be notified of a change to address XYZ". In the Plutus.Contract.App module, as well as in the unit tests, i is fixed to Plutus.Contract.Prompt.Event.Event and o is Plutus.Contract.Prompt.Hooks.Hooks. Each instance of a contract is represented by a Plutus.Contract.Record.Record value, and the state can be advanced using Plutus.Contract.Resumable.updateRecord. See the note [Handling state in contracts] for details.

1. nix build -f default.nix localPackages.plutus-contract

Alternatively:

1. cd plutus-contract
2. nix-shell
3. cabal build <name-of-example> for example cabal build contract-exe-guessing-game

To build the docker image for the guessing game contract:

1. nix build -f default.nix plutus-contract.docker
2. docker load -i result