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Fe is an emerging smart contract language for the Ethereum blockchain.

Build Status Coverage

NOTE: The larger part of the master branch will be replaced with the brand-new implementation, which is currently under development in the fe-v2 branch. Please refer to the branch if you kindly contribute to Fe

Overview

Fe is a statically typed language for the Ethereum Virtual Machine (EVM). It is inspired by Python and Rust which makes it easy to learn -- especially for new developers entering the Ethereum ecosystem.

Features & Goals

  • Bounds and overflow checking
  • Decidability by limitation of dynamic program behavior
  • More precise gas estimation (as a consequence of decidability)
  • Static typing
  • Pure function support
  • Restrictions on reentrancy
  • Static looping
  • Module imports
  • Standard library
  • Usage of YUL IR to target both EVM and eWASM
  • WASM compiler binaries for enhanced portability and in-browser compilation of Fe contracts
  • Implementation in a powerful, systems-oriented language (Rust) with strong safety guarantees to reduce risk of compiler bugs

Additional information about design goals and background can be found in the official announcement.

Language Specification

We aim to provide a full language specification that should eventually be used to formally verify the correctness of the compiler. A work in progress draft of the specification can be found here.

Progress

Fe development is still in its early stages. We have a basic Roadmap for 2021 that we want to follow. We generally try to drive the development by working through real world use cases. Our next goal is to provide a working Uniswap implementation in Fe which will help us to advance and form the language.

Fe had its first alpha release January 2021 and is now following a monthly release cycle.

Getting started

To compile Fe code:

  1. Run fe path/to/fe_source.fe
  2. Fe creates a directory output in the current working directory that contains the compiled binary and abi.

Run fe --help to explore further options.

Examples

The following is a simple contract implemented in Fe.

struct Signed {
    book_msg: String<100>
}

contract GuestBook {
    messages: Map<address, String<100>>

    pub fn sign(self, ctx: Context, book_msg: String<100>) {
        self.messages[ctx.msg_sender()] = book_msg
        ctx.emit(Signed(book_msg: book_msg))
    }

    pub fn get_msg(self, addr: address) -> String<100> {
        return self.messages[addr].to_mem()
    }
}

A lot more working examples can be found in our test fixtures directory.

The most advanced example that we can provide at this point is an implementation of the Uniswap-V2 core contracts.

Community

License

The Fe implementation is split into several crates. Crates that depend on the solidity compiler (directly or indirectly) are licensed GPL-3.0-or-later. This includes the fe CLI tool, yulc, driver, tests, and test-utils.

The remaining crates are licensed Apache-2.0. This includes the parser, analyzer, mir, abi, and common.