hebi 0.1.1.0.9.9

A simple pythonic programming language for Smart Contracts on Cardano

hebi

This is an implementation of smart contracts for Cardano which are written in a very strict subset of valid Python. The general philosophy of this project is to write a compiler that ensure the following:

If the program compiles then:

1. it is a valid Python program
2. the output running it with python is the same as running it on-chain.

Why hebi?

• 100% valid Python. Leverage the existing tool stack for Python, syntax highlighting, linting, debugging, unit-testing, property-based testing, verification
• Intuitive. Just like Python.
• Flexible. Imperative, functional, the way you want it.
• Efficient & Secure. Static type inference ensures strict typing and optimized code

Note this is the sister project of eopsin. It uses an even more restricted subset of python (for example no if & while). The benefit is that the resulting code is greatly reduced in size and cpu/memory consumption.

Eopsin is more comfortable to use than hebi. If you want to start building, write your contract in eopsin first. Then, after everything works to your pleasing, try to port to hebi and enjoy the performance gains.

Getting Started

Example repository

Check out this example repository for a quick start in setting up a development environment and compiling some sample contracts yours:

https://github.com/OpShin/eopsin-example

You can replace the contracts in your local copy of the repository with code from the examples section here to start exploring different contracts.

Developer Community and Questions

The eopsin repository contains a discussions page. Feel free to open up a new discussion with questions regarding development using hebi and using certain features. Others may be able to help you and will also benefit from the previously shared questions.

Check out the community here

You can also chat with other developers in the welcoming discord community of OpShin

Installation

Install Python 3.8. Then run

python3.8 -m pip install hebi

Writing a Smart Contract

A short non-complete introduction in starting to write smart contracts follows.

1. Make sure you understand EUTxOs, Addresses, Validators etc on Cardano. There is a wonderful crashcourse by @KtorZ. The contract will work on these concepts
2. Make sure you understand python. Eopsin works like python and uses python. There are tons of tutorials for python, choose what suits you best.
3. Make sure your contract is valid python and the types check out. Write simple contracts first and run them using hebi eval to get a feeling for how they work.
4. Make sure your contract is valid hebi code. Run hebi compile and look at the compiler erros for guidance along what works and doesn't work and why.
5. Dig into the examples to understand common patterns. Check out the prelude for understanding how the Script Context is structured and how complex datums are defined.
6. Check out the sample repository to find a sample setup for developing your own contract.

In summary, a smart contract in hebi is defined by the function validator in your contract file. The function validates that a specific value can be spent, minted, burned, withdrawn etc, depending on where it is invoked/used as a credential. If the function fails (i.e. raises an error of any kind such as a KeyError or AssertionError) the validation is denied, and the funds can not be spent, minted, burned etc.

There is a subtle difference here in comparison to most other Smart Contract languages. In hebi a validator may return anything (in particular also False) - as long as it does not fail, the execution is considered valid. This is more similar to how contracts in Solidity always pass, unless they run out of gas or hit an error. So make sure to assert what you want to ensure to hold for validation!

A simple contract called the "Gift Contract" verifies that only specific wallets can withdraw money. They are authenticated by a signature. If you don't understand what a pubkeyhash is and how this validates anything, check out this gentle introduction into Cardanos EUTxO. Also see the tutorial by pycardano for explanations on what each of the parameters to the validator means and how to build transactions with the contract.

from hebi.prelude import *

@dataclass()
class CancelDatum(PlutusData):
    pubkeyhash: bytes


def validator(datum: CancelDatum, redeemer: None, context: ScriptContext) -> None:
    assert datum.pubkeyhash in context.tx_info.signatories, "Required signature missing"

All contracts written in hebi are 100% valid python. Minting policies follow the same structure, but expect a value of type None as first argument. See the examples directory for more.

Compiling

Write your program in python. You may start with the content of examples. Arguments to scripts are passed in as Plutus Data objects in JSON notation.

You can run any of the following commands

# Evaluate script in Python - this can be used to make sure there are no obvious errors
hebi eval examples/smart_contracts/assert_sum.py "{\"int\": 4}" "{\"int\": 38}" "{\"constructor\": 0, \"fields\": []}"

# Compile script to 'uplc', the Cardano Smart Contract assembly
hebi compile examples/smart_contracts/assert_sum.py

Deploying

The deploy process generates all artifacts required for usage with common libraries like pycardano, lucid and the cardano-cli.

# Automatically generate all artifacts needed for using this contract
hebi build examples/smart_contracts/assert_sum.py

See the tutorial by pycardano for explanations how to build transactions with eopsin contracts. Contracts in hebi are invoked the same, so you can just follow the tutorial there.

The small print

Not every valid python program is a valid smart contract. Not all language features of python will or can be supported. The reasons are mainly of practical nature (i.e. we can't infer types when functions like eval are allowed). Specifically, only a pure subset of python is allowed. Further, only immutable objects may be generated.

For your program to be accepted, make sure to only make use of language constructs supported by the compiler. You will be notified of which constructs are not supported when trying to compile.

Name

Hebi is japanese for "snake", which is a play on words on python, the underlying language.

Versioning scheme

Since this project builds on top of eopsin, it has a particular versioning scheme. The first three numbers indicate the version of hebi (starting at 0.1.0). Then follows the latest version number of eopsin which was merged into the project (starting at 0.9.3). This is intended to help navigating releases among both packages, where it might be important that a recent eopsin release is integrated that contains a security patch.

Contributing

Architecture

This program consists of a few independent components:

1. An aggressive static type inferencer
2. Rewriting tools to simplify complex python expressions
3. A compiler from a subset of python into UPLC

Debugging artefacts

For debugging purposes, you can also run

# Compile script to 'uplc', and evaluate the script in UPLC (for debugging purposes)
python3 -m hebi eval_uplc examples/smart_contracts/assert_sum.py "{\"int\": 4}" "{\"int\": 38}" "{\"constructor\": 0, \"fields\": []}"

# Compile script to 'pluto', an intermediate language (for debugging purposes)
python3 -m hebi compile_pluto examples/smart_contracts/assert_sum.py

Sponsoring

You can sponsor the development of hebi through GitHub or Teiki or just by sending ADA. Drop me a message on social media and let me know what it is for.

• Teiki Stake your ada to support OpShin at Teiki
• GitHub Sponsor the developers of this project through the button "Sponsor" next to them
• ADA Donation in ADA can be submitted to $opshin or addr1qyz3vgd5xxevjy2rvqevz9n7n7dney8n6hqggp23479fm6vwpj9clsvsf85cd4xc59zjztr5zwpummwckmzr2myjwjns74lhmr.

Supporters